Desafío de rendimiento de C ++: conversión de entero a std :: string

¿Alguien puede superar el rendimiento de mi número entero al código std :: string, vinculado a continuación?

Ya hay varias preguntas que explican cómo convertir un entero en una std::string en C ++, como esta , pero ninguna de las soluciones proporcionadas es eficiente.

Aquí hay un código de comstackción listo para algunos métodos comunes para competir contra:

  • La “forma C ++”, utilizando stringstream: http://ideone.com/jh3Sa
  • sprintf, que los SO-ers generalmente recomiendan al consciente del rendimiento: http://ideone.com/82kwR

Contrario a la creencia popular , boost::lexical_cast tiene su propia implementación ( white paper ) y no usa operadores de inserción de stringstream y numéricos. Realmente me gustaría ver su rendimiento comparado, porque esta otra pregunta sugiere que es miserable .

Y mi propia contribución, que es competitiva en las computadoras de escritorio, y demuestra un enfoque que se ejecuta a toda velocidad en los sistemas integrados también, a diferencia de los algoritmos que dependen del módulo entero:

  • Algoritmos de Ben: http://ideone.com/SsEUW

Si desea utilizar ese código, lo pondré a disposición bajo una licencia BSD simplificada (se permite el uso comercial, se requiere atribución). Solo pregunta.

Finalmente, la función ltoa no es estándar, pero está ampliamente disponible.

  • ltoa version, para cualquiera que tenga un comstackdor que lo proporcione (ideone does not): http://ideone.com/T5Wim

Voy a publicar mis medidas de rendimiento como una respuesta en breve.

Reglas para algoritmos

  • Proporcione el código para una conversión de enteros con signo y sin signo de 32 bits como mínimo en decimal.
  • Producir salida como std::string .
  • No hay trucos que sean incompatibles con el enhebrado y las señales (por ejemplo, búferes estáticos).
  • Puede asumir un juego de caracteres ASCII.
  • Asegúrese de probar su código en INT_MIN en una máquina complementaria de dos donde el valor absoluto no es representable.
  • Idealmente, la salida debería ser carácter por carácter idéntica a la versión canónica de C ++ utilizando stringstream , http://ideone.com/jh3Sa , pero cualquier cosa que sea claramente comprensible como el número correcto también está bien.
  • NUEVO : Aunque puede usar las opciones de comstackdor y optimizador (excepto las completamente deshabilitadas) que desee para la comparación, el código también debe comstackr y proporcionar resultados correctos al menos en VC ++ 2010 y g ++.

Discusión esperada

Además de mejores algoritmos, también me gustaría obtener algunos puntos de referencia en varias plataformas y comstackdores diferentes (usemos el rendimiento MB / s como nuestra unidad de medida estándar). Creo que el código para mi algoritmo (sé que el sprintf benchmark toma algunos atajos, ahora está fijo) es un comportamiento bien definido por el estándar, al menos bajo el supuesto ASCII, pero si ve algún comportamiento indefinido o entradas para las cuales el la salida no es válida, por favor, indíquelo.

Conclusiones

Se realizan diferentes algoritmos para g ++ y VC2010, probablemente debido a las diferentes implementaciones de std::string en cada uno. VC2010 claramente hace un mejor trabajo con NRVO, deshacerse del retorno por valor ayudó solo en gcc.

Se encontró un código que supera el sprintf en un orden de magnitud. ostringstream queda rezagado por un factor de 50 o más.

El ganador del desafío es user434507, que produce un código que ejecuta 350% de mi velocidad en gcc. Las entradas adicionales están cerradas debido a los caprichos de la comunidad SO.

Los actuales campeones de velocidad (¿finales?) Son:

  • Para gcc: user434507, a 8 veces más rápido que sprintf : http://ideone.com/0uhhX
  • Para Visual C ++: Timo, a 15 veces más rápido que sprintf : http://ideone.com/VpKO3

 #include  const char digit_pairs[201] = { "00010203040506070809" "10111213141516171819" "20212223242526272829" "30313233343536373839" "40414243444546474849" "50515253545556575859" "60616263646566676869" "70717273747576777879" "80818283848586878889" "90919293949596979899" }; std::string& itostr(int n, std::string& s) { if(n==0) { s="0"; return s; } int sign = -(n<0); unsigned int val = (n^sign)-sign; int size; if(val>=10000) { if(val>=10000000) { if(val>=1000000000) size=10; else if(val>=100000000) size=9; else size=8; } else { if(val>=1000000) size=7; else if(val>=100000) size=6; else size=5; } } else { if(val>=100) { if(val>=1000) size=4; else size=3; } else { if(val>=10) size=2; else size=1; } } size -= sign; s.resize(size); char* c = &s[0]; if(sign) *c='-'; c += size-1; while(val>=100) { int pos = val % 100; val /= 100; *(short*)(c-1)=*(short*)(digit_pairs+2*pos); c-=2; } while(val>0) { *c--='0' + (val % 10); val /= 10; } return s; } std::string& itostr(unsigned val, std::string& s) { if(val==0) { s="0"; return s; } int size; if(val>=10000) { if(val>=10000000) { if(val>=1000000000) size=10; else if(val>=100000000) size=9; else size=8; } else { if(val>=1000000) size=7; else if(val>=100000) size=6; else size=5; } } else { if(val>=100) { if(val>=1000) size=4; else size=3; } else { if(val>=10) size=2; else size=1; } } s.resize(size); char* c = &s[size-1]; while(val>=100) { int pos = val % 100; val /= 100; *(short*)(c-1)=*(short*)(digit_pairs+2*pos); c-=2; } while(val>0) { *c--='0' + (val % 10); val /= 10; } return s; } 

Esto explotará en sistemas que no permiten accesos de memoria no alineados (en cuyo caso, la primera asignación desalineada a través de *(short*) provocaría una segfault), pero debería funcionar muy bien de lo contrario.

Una cosa importante es minimizar el uso de std::string . (Irónico, lo sé). En Visual Studio, por ejemplo, la mayoría de las llamadas a métodos de std :: string no están en línea, incluso si especifica / Ob2 en las opciones del comstackdor. Entonces, incluso algo tan trivial como una llamada a std::string::clear() , que se puede esperar que sea muy rápido, puede tomar 100 clockticks cuando se vincula CRT como una biblioteca estática, y hasta 300 clockticks cuando se vinculan como un DLL.

Por la misma razón, devolver por referencia es mejor porque evita una asignación, un constructor y un destructor.

Ah, impresionante desafío por cierto … Me he divertido mucho con esto.

Tengo dos algoritmos para enviar (el código está en la parte inferior si quieres saltarte). En mis comparaciones, requiero que la función devuelva una cadena y que pueda manejar int y unsigned int. Comparar cosas que no construyen una cadena con las que sí lo hacen realmente no tiene sentido.

La primera es una implementación divertida que no usa ninguna tabla de búsqueda precalculada o división / módulo explícito. Este es competitivo con los demás con gcc y con todos menos con Timo’s en msvc (por una buena razón que explico a continuación). El segundo algoritmo es mi presentación real para el mayor rendimiento. En mis pruebas, supera a todas las demás en gcc y msvc.

Creo que sé por qué algunos de los resultados en MSVC son muy buenos. std :: string tiene dos constructores relevantes std::string(char* str, size_t n)
y
std::string(ForwardIterator b, ForwardIterator e)
gcc hace lo mismo para ambos … es decir, usa el segundo para implementar el primero. El primer constructor se puede implementar de manera significativamente más eficiente que eso y MSVC lo hace. El beneficio adicional de esto es que en algunos casos (como mi código rápido y el código de Timo) el constructor de cadenas puede estar en línea. De hecho, solo cambiar entre estos constructores en MSVC es casi una diferencia de 2 veces para mi código.

Mis resultados de prueba de rendimiento:

Fuentes de código:

– Voigt
– Timo
– ergosys
– user434507
– usuario-voigt-timo
– diversión de hopman
– hopman-rápido

gcc 4.4.5 -O2 en Ubuntu 10.10 de 64 bits, Core i5

 hopman_fun: 124.688 MB / sec --- 8.020 s
 hopman_fast: 137.552 MB / sec --- 7.270 s
 voigt: 120.192 MB / s --- 8.320 s
 user_voigt_timo: 97.9432 MB / sec --- 10.210 s
 timo: 120.482 MB / seg --- 8.300 s
 usuario: 97.7517 MB / sec --- 10.230 s
 ergosys: 101.42 MB / sec --- 9.860 s

MSVC 2010 de 64 bits / Ox en Windows 7 de 64 bits, Core i5

 hopman_fun: 127 MB / sec --- 7.874 s
 hopman_fast: 259 MB / s --- 3.861 s
 voigt: 221.435 MB / sec --- 4.516 s
 user_voigt_timo: 195.695 MB / sec --- 5.110 s
 timo: 253.165 MB / s --- 3.950 s
 usuario: 212.63 MB / sec --- 4.703 s
 ergosys: 78.0518 MB / seg --- 12.812 s

Aquí hay algunos resultados y un marco de prueba / sincronización en ideone
http://ideone.com/XZRqp
Tenga en cuenta que ideone es un entorno de 32 bits. Ambos algoritmos sufren de eso, pero hopman_fast es al menos aún competitivo.

Tenga en cuenta que para aquellos dos que no construyen una cadena, agregué la siguiente plantilla de función:

 template  std::string itostr(T t) { std::string ret; itostr(t, ret); return ret; } 

Ahora, para mi código … primero el más divertido:

  // hopman_fun template  T reduce2(T v) { T k = ((v * 410) >> 12) & 0x000F000F000F000Full; return (((v - k * 10) << 8) + k); } template  T reduce4(T v) { T k = ((v * 10486) >> 20) & 0xFF000000FFull; return reduce2(((v - k * 100) << 16) + (k)); } typedef unsigned long long ull; inline ull reduce8(ull v) { ull k = ((v * 3518437209u) >> 45); return reduce4(((v - k * 10000) << 32) + (k)); } template  std::string itostr(T o) { union { char str[16]; unsigned short u2[8]; unsigned u4[4]; unsigned long long u8[2]; }; unsigned v = o < 0 ? ~o + 1 : o; u8[0] = (ull(v) * 3518437209u) >> 45; u8[0] = (u8[0] * 28147497672ull); u8[1] = v - u2[3] * 100000000; u8[1] = reduce8(u8[1]); char* f; if (u2[3]) { u2[3] = reduce2(u2[3]); f = str + 6; } else { unsigned short* k = u4[2] ? u2 + 4 : u2 + 6; f = *k ? (char*)k : (char*)(k + 1); } if (!*f) f++; u4[1] |= 0x30303030; u4[2] |= 0x30303030; u4[3] |= 0x30303030; if (o < 0) *--f = '-'; return std::string(f, (str + 16) - f); } 

Y luego el rápido:

  // hopman_fast struct itostr_helper { static unsigned out[10000]; itostr_helper() { for (int i = 0; i < 10000; i++) { unsigned v = i; char * o = (char*)(out + i); o[3] = v % 10 + '0'; o[2] = (v % 100) / 10 + '0'; o[1] = (v % 1000) / 100 + '0'; o[0] = (v % 10000) / 1000; if (o[0]) o[0] |= 0x30; else if (o[1] != '0') o[0] |= 0x20; else if (o[2] != '0') o[0] |= 0x10; else o[0] |= 0x00; } } }; unsigned itostr_helper::out[10000]; itostr_helper hlp_init; template  std::string itostr(T o) { typedef itostr_helper hlp; unsigned blocks[3], *b = blocks + 2; blocks[0] = o < 0 ? ~o + 1 : o; blocks[2] = blocks[0] % 10000; blocks[0] /= 10000; blocks[2] = hlp::out[blocks[2]]; if (blocks[0]) { blocks[1] = blocks[0] % 10000; blocks[0] /= 10000; blocks[1] = hlp::out[blocks[1]]; blocks[2] |= 0x30303030; b--; } if (blocks[0]) { blocks[0] = hlp::out[blocks[0] % 10000]; blocks[1] |= 0x30303030; b--; } char* f = ((char*)b); f += 3 - (*f >> 4); char* str = (char*)blocks; if (o < 0) *--f = '-'; return std::string(f, (str + 12) - f); } 

Datos de referencia para el código proporcionado en la pregunta:

En ideone (gcc 4.3.4):

  • cadenas de caracteres: 4.4 MB / s
  • sprintf: 25.0 MB / s
  • mío (Ben Voigt) : 55.8 MB / s
  • Timo : 58.5 MB / s
  • user434507 : 199 MB / s
  • híbrido Ben-Timo-507 de user434507 : 263 MB / s

Core i7, Windows 7 de 64 bits, 8 GB de RAM, Visual C ++ 2010 de 32 bits:

cl /Ox /EHsc

  • cadenas de caracteres: 3,39 MB / s, 3,67 MB / s
  • sprintf: 16.8 MB / s, 16.2 MB / s
  • mío: 194 MB / s, 207 MB / s (con PGO activado: 250 MB / s)

Core i7, Windows 7 de 64 bits, 8 GB de RAM, Visual C ++ 2010 de 64 bits:

cl /Ox /EHsc

  • cadenas de caracteres: 4.42 MB / s, 4.92 MB / s
  • sprintf: 21.0 MB / s, 20.8 MB / s
  • mío: 238 MB / s, 228 MB / s

Core i7, Windows 7 de 64 bits, 8 GB de RAM, cygwin gcc 4.3.4:

g++ -O3

  • cadenas de caracteres: 2,19 MB / s, 2,17 MB / s
  • sprintf: 13.1 MB / s, 13.4 MB / s
  • mío: 30.0 MB / s, 30.2 MB / s

editar : Iba a agregar mi propia respuesta, pero la pregunta estaba cerrada, así que la añado aquí. 🙂 Escribí mi propio algoritmo y logré una mejora decente con respecto al código de Ben, aunque solo lo probé en MSVC 2010. También hice un punto de referencia de todas las implementaciones presentadas hasta ahora, usando la misma configuración de prueba que estaba en el original de Ben. código. – Timo

Intel Q9450, Win XP 32bit, MSVC 2010

cl /O2 /EHsc

  • cadena de caracteres: 2.87 MB / s
  • sprintf: 16.1 MB / s
  • Ben: 202 MB / s
  • Ben (buffer sin signo): 82.0 MB / s
  • ergosys (versión actualizada): 64.2 MB / s
  • user434507: 172 MB / s
  • Timo: 241 MB / s

 const char digit_pairs[201] = { "00010203040506070809" "10111213141516171819" "20212223242526272829" "30313233343536373839" "40414243444546474849" "50515253545556575859" "60616263646566676869" "70717273747576777879" "80818283848586878889" "90919293949596979899" }; static const int BUFFER_SIZE = 11; std::string itostr(int val) { char buf[BUFFER_SIZE]; char *it = &buf[BUFFER_SIZE-2]; if(val>=0) { int div = val/100; while(div) { memcpy(it,&digit_pairs[2*(val-div*100)],2); val = div; it-=2; div = val/100; } memcpy(it,&digit_pairs[2*val],2); if(val<10) it++; } else { int div = val/100; while(div) { memcpy(it,&digit_pairs[-2*(val-div*100)],2); val = div; it-=2; div = val/100; } memcpy(it,&digit_pairs[-2*val],2); if(val<=-10) it--; *it = '-'; } return std::string(it,&buf[BUFFER_SIZE]-it); } std::string itostr(unsigned int val) { char buf[BUFFER_SIZE]; char *it = (char*)&buf[BUFFER_SIZE-2]; int div = val/100; while(div) { memcpy(it,&digit_pairs[2*(val-div*100)],2); val = div; it-=2; div = val/100; } memcpy(it,&digit_pairs[2*val],2); if(val<10) it++; return std::string((char*)it,(char*)&buf[BUFFER_SIZE]-(char*)it); } 

Si bien la información que recibimos aquí para los algoritmos es bastante buena, creo que la pregunta está “rota”, y explicaré por qué pienso esto:

La pregunta solicita tomar el rendimiento de la conversión int -> std::string , y esto puede ser de interés cuando se compara un método comúnmente disponible, como diferentes implementaciones de cadenas de caracteres o boost :: lexical_cast. Sin embargo, no tiene sentido cuando se solicita un nuevo código , un algoritmo especializado, para hacer esto. La razón es que int2string siempre implicará la asignación de heap desde std :: string y si estamos tratando de exprimir el último de nuestro algoritmo de conversión, no creo que tenga sentido mezclar estas mediciones con las asignaciones de heap realizadas por std: :cuerda. Si quiero una conversión de rendimiento siempre usaré un buffer de tamaño fijo y ciertamente nunca asignaré nada en el montón.

Para resumir, creo que los tiempos deberían dividirse:

  • Primero, la conversión más rápida (int -> buffer fijo).
  • Segundo, el tiempo de copia (buffer fijo -> std :: string).
  • En tercer lugar, verificar cómo la asignación std :: string se puede usar directamente como buffer, para guardar la copia.

Estos aspectos no deben mezclarse en un solo momento, en mi humilde opinión.

No puedo probar bajo VS, pero esto parece ser más rápido que su código para g ++, aproximadamente 10%. Probablemente podría ajustarse, los valores de decisión elegidos son conjeturas. int solo, lo siento.

 typedef unsigned buf_t; static buf_t * reduce(unsigned val, buf_t * stp) { unsigned above = val / 10000; if (above != 0) { stp = reduce(above, stp); val -= above * 10000; } buf_t digit = val / 1000; *stp++ = digit + '0'; val -= digit * 1000; digit = val / 100; *stp++ = digit + '0'; val -= digit * 100; digit = val / 10; *stp++ = digit + '0'; val -= digit * 10; *stp++ = val + '0'; return stp; } std::string itostr(int input) { buf_t buf[16]; if(input == INT_MIN) { char buf2[16]; std::sprintf(buf2, "%d", input); return std::string(buf2); } // handle negative unsigned val = input; if(input < 0) val = -input; buf[0] = '0'; buf_t* endp = reduce(val, buf+1); *endp = 127; buf_t * stp = buf+1; while (*stp == '0') stp++; if (stp == endp) stp--; if (input < 0) { stp--; *stp = '-'; } return std::string(stp, endp); } 

actualicé mi respuesta … modp_ufast …

 Integer To String Test (Type 1) [modp_ufast]Numbers: 240000000 Total: 657777786 Time: 1.1633sec Rate:206308473.0686nums/sec [sprintf] Numbers: 240000000 Total: 657777786 Time: 24.3629sec Rate: 9851045.8556nums/sec [karma] Numbers: 240000000 Total: 657777786 Time: 5.2389sec Rate: 45810870.7171nums/sec [strtk] Numbers: 240000000 Total: 657777786 Time: 3.3126sec Rate: 72450283.7492nums/sec [so ] Numbers: 240000000 Total: 657777786 Time: 3.0828sec Rate: 77852152.8820nums/sec [timo ] Numbers: 240000000 Total: 657777786 Time: 4.7349sec Rate: 50687912.9889nums/sec [voigt] Numbers: 240000000 Total: 657777786 Time: 5.1689sec Rate: 46431985.1142nums/sec [hopman] Numbers: 240000000 Total: 657777786 Time: 4.6169sec Rate: 51982554.6497nums/sec Press any key to continue . . . Integer To String Test(Type 2) [modp_ufast]Numbers: 240000000 Total: 660000000 Time: 0.5072sec Rate:473162716.4618nums/sec [sprintf] Numbers: 240000000 Total: 660000000 Time: 22.3483sec Rate: 10739062.9383nums/sec [karma] Numbers: 240000000 Total: 660000000 Time: 4.2471sec Rate: 56509024.3035nums/sec [strtk] Numbers: 240000000 Total: 660000000 Time: 2.1683sec Rate:110683636.7123nums/sec [so ] Numbers: 240000000 Total: 660000000 Time: 2.7133sec Rate: 88454602.1423nums/sec [timo ] Numbers: 240000000 Total: 660000000 Time: 2.8030sec Rate: 85623453.3872nums/sec [voigt] Numbers: 240000000 Total: 660000000 Time: 3.4019sec Rate: 70549286.7776nums/sec [hopman] Numbers: 240000000 Total: 660000000 Time: 2.7849sec Rate: 86178023.8743nums/sec Press any key to continue . . . Integer To String Test (type 3) [modp_ufast]Numbers: 240000000 Total: 505625000 Time: 1.6482sec Rate:145610315.7819nums/sec [sprintf] Numbers: 240000000 Total: 505625000 Time: 20.7064sec Rate: 11590618.6109nums/sec [karma] Numbers: 240000000 Total: 505625000 Time: 4.3036sec Rate: 55767734.3570nums/sec [strtk] Numbers: 240000000 Total: 505625000 Time: 2.9297sec Rate: 81919227.9275nums/sec [so ] Numbers: 240000000 Total: 505625000 Time: 3.0278sec Rate: 79266003.8158nums/sec [timo ] Numbers: 240000000 Total: 505625000 Time: 4.0631sec Rate: 59068204.3266nums/sec [voigt] Numbers: 240000000 Total: 505625000 Time: 4.5616sec Rate: 52613393.0285nums/sec [hopman] Numbers: 240000000 Total: 505625000 Time: 4.1248sec Rate: 58184194.4569nums/sec Press any key to continue . . . int ufast_utoa10(unsigned int value, char* str) { #define JOIN(N) N "0", N "1", N "2", N "3", N "4", N "5", N "6", N "7", N "8", N "9" #define JOIN2(N) JOIN(N "0"), JOIN(N "1"), JOIN(N "2"), JOIN(N "3"), JOIN(N "4"), \ JOIN(N "5"), JOIN(N "6"), JOIN(N "7"), JOIN(N "8"), JOIN(N "9") #define JOIN3(N) JOIN2(N "0"), JOIN2(N "1"), JOIN2(N "2"), JOIN2(N "3"), JOIN2(N "4"), \ JOIN2(N "5"), JOIN2(N "6"), JOIN2(N "7"), JOIN2(N "8"), JOIN2(N "9") #define JOIN4 JOIN3("0"), JOIN3("1"), JOIN3("2"), JOIN3("3"), JOIN3("4"), \ JOIN3("5"), JOIN3("6"), JOIN3("7"), JOIN3("8"), JOIN3("9") #define JOIN5(N) JOIN(N), JOIN(N "1"), JOIN(N "2"), JOIN(N "3"), JOIN(N "4"), \ JOIN(N "5"), JOIN(N "6"), JOIN(N "7"), JOIN(N "8"), JOIN(N "9") #define JOIN6 JOIN5(), JOIN5("1"), JOIN5("2"), JOIN5("3"), JOIN5("4"), \ JOIN5("5"), JOIN5("6"), JOIN5("7"), JOIN5("8"), JOIN5("9") #define F(N) ((N) >= 100 ? 3 : (N) >= 10 ? 2 : 1) #define F10(N) F(N),F(N+1),F(N+2),F(N+3),F(N+4),F(N+5),F(N+6),F(N+7),F(N+8),F(N+9) #define F100(N) F10(N),F10(N+10),F10(N+20),F10(N+30),F10(N+40),\ F10(N+50),F10(N+60),F10(N+70),F10(N+80),F10(N+90) static const short offsets[] = { F100(0), F100(100), F100(200), F100(300), F100(400), F100(500), F100(600), F100(700), F100(800), F100(900)}; static const char table1[][4] = { JOIN("") }; static const char table2[][4] = { JOIN2("") }; static const char table3[][4] = { JOIN3("") }; static const char table4[][5] = { JOIN4 }; static const char table5[][4] = { JOIN6 }; #undef JOIN #undef JOIN2 #undef JOIN3 #undef JOIN4 char *wstr; int remains[2]; unsigned int v2; if (value >= 100000000) { v2 = value / 10000; remains[0] = value - v2 * 10000; value = v2; v2 = value / 10000; remains[1] = value - v2 * 10000; value = v2; wstr = str; if (value >= 1000) { *(__int32 *) wstr = *(__int32 *) table4[value]; wstr += 4; } else { *(__int32 *) wstr = *(__int32 *) table5[value]; wstr += offsets[value]; } *(__int32 *) wstr = *(__int32 *) table4[remains[1]]; wstr += 4; *(__int32 *) wstr = *(__int32 *) table4[remains[0]]; wstr += 4; *wstr = 0; return (wstr - str); } else if (value >= 10000) { v2 = value / 10000; remains[0] = value - v2 * 10000; value = v2; wstr = str; if (value >= 1000) { *(__int32 *) wstr = *(__int32 *) table4[value]; wstr += 4; *(__int32 *) wstr = *(__int32 *) table4[remains[0]]; wstr += 4; *wstr = 0; return 8; } else { *(__int32 *) wstr = *(__int32 *) table5[value]; wstr += offsets[value]; *(__int32 *) wstr = *(__int32 *) table4[remains[0]]; wstr += 4; *wstr = 0; return (wstr - str); } } else { if (value >= 1000) { *(__int32 *) str = *(__int32 *) table4[value]; str += 4; *str = 0; return 4; } else if (value >= 100) { *(__int32 *) str = *(__int32 *) table3[value]; return 3; } else if (value >= 10) { *(__int16 *) str = *(__int16 *) table2[value]; str += 2; *str = 0; return 2; } else { *(__int16 *) str = *(__int16 *) table1[value]; return 1; } } } int ufast_itoa10(int value, char* str) { if (value < 0) { *(str++) = '-'; return ufast_utoa10(-value, str) + 1; } else return ufast_utoa10(value, str); } void ufast_test() { print_mode("[modp_ufast]"); std::string s; s.reserve(32); std::size_t total_length = 0; strtk::util::timer t; t.start(); char buf[128]; int len; for (int i = (-max_i2s / 2); i < (max_i2s / 2); ++i) { #ifdef enable_test_type01 s.resize(ufast_itoa10(((i & 1) ? i : -i), const_cast(s.c_str()))); total_length += s.size(); #endif #ifdef enable_test_type02 s.resize(ufast_itoa10(max_i2s + i, const_cast(s.c_str()))); total_length += s.size(); #endif #ifdef enable_test_type03 s.resize(ufast_itoa10(randval[(max_i2s + i) & 1023], const_cast(s.c_str()))); total_length += s.size(); #endif } t.stop(); printf("Numbers:%10lu\tTotal:%12lu\tTime:%8.4fsec\tRate:%14.4fnums/sec\n", static_cast(3 * max_i2s), static_cast(total_length), t.time(), (3.0 * max_i2s) / t.time()); } 

He tenido esto sentado por un tiempo y finalmente logré publicarlo.

Unos pocos métodos más en comparación con la doble palabra a la vez hopman_fast . Los resultados corresponden a la std :: string optimizada de cadena corta de GCC, ya que de lo contrario las diferencias de rendimiento quedan oscurecidas por la sobrecarga del código de administración de cadenas de copia sobre escritura. El rendimiento se mide de la misma manera que en cualquier otro lugar de este tema, los recuentos de ciclo corresponden a las partes de serialización brutas del código antes de copiar el búfer de salida en una cadena.

 HOPMAN_FAST - performance reference TM_CPP, TM_VEC - scalar and vector versions of Terje Mathisen algorithm WM_VEC - intrinsics implementation of Wojciech Mula's vector algorithm AK_BW - word-at-a-time routine with a jump table that fills a buffer in reverse AK_FW - forward-stepping word-at-a-time routine with a jump table in assembly AK_UNROLLED - generic word-at-a-time routine that uses an unrolled loop 

Rendimiento

Costo bruto

Switches de tiempo de comstackción

-DVSTRING: habilita cadenas de SSO para configuraciones de GCC antiguas
-DBSR1 – permite un log10 rápido
-DRDTSC – habilita contadores de ciclo

 #include  #include  #include  #include  #include  #include  #include  #include  #include  #include  /* Uncomment to run */ // #define HOPMAN_FAST // #define TM_CPP // #define TM_VEC // #define WM_VEC // #define AK_UNROLLED // #define AK_BW // #define AK_FW using namespace std; #ifdef VSTRING #include  typedef __gnu_cxx::__vstring string_type; #else typedef string string_type; #endif namespace detail { #ifdef __GNUC__ #define ALIGN(N) __attribute__ ((aligned(N))) #define PACK __attribute__ ((packed)) inline size_t num_digits(unsigned u) { struct { uint32_t count; uint32_t max; } static digits[32] ALIGN(64) = { { 1, 9 }, { 1, 9 }, { 1, 9 }, { 1, 9 }, { 2, 99 }, { 2, 99 }, { 2, 99 }, { 3, 999 }, { 3, 999 }, { 3, 999 }, { 4, 9999 }, { 4, 9999 }, { 4, 9999 }, { 4, 9999 }, { 5, 99999 }, { 5, 99999 }, { 5, 99999 }, { 6, 999999 }, { 6, 999999 }, { 6, 999999 }, { 7, 9999999 }, { 7, 9999999 }, { 7, 9999999 }, { 7, 9999999 }, { 8, 99999999 }, { 8, 99999999 }, { 8, 99999999 }, { 9, 999999999 }, { 9, 999999999 }, { 9, 999999999 }, { 10, UINT_MAX }, { 10, UINT_MAX } }; #if (defined(i386) || defined(__x86_64__)) && (defined(BSR1) || defined(BSR2)) size_t l = u; #if defined(BSR1) __asm__ __volatile__ ( "bsrl %k0, %k0 \n\t" "shlq $32, %q1 \n\t" "movq %c2(,%0,8), %0\n\t" "cmpq %0, %q1 \n\t" "seta %b1 \n\t" "addl %1, %k0 \n\t" : "+r" (l), "+r"(u) : "i"(digits) : "cc" ); return l; #else __asm__ __volatile__ ( "bsr %0, %0;" : "+r" (l) ); return digits[l].count + ( u > digits[l].max ); #endif #else size_t l = (u != 0) ? 31 - __builtin_clz(u) : 0; return digits[l].count + ( u > digits[l].max ); #endif } #else inline unsigned msb_u32(unsigned x) { static const unsigned bval[] = { 0,1,2,2,3,3,3,3,4,4,4,4,4,4,4,4 }; unsigned base = 0; if (x & (unsigned) 0xFFFF0000) { base += 32/2; x >>= 32/2; } if (x & (unsigned) 0x0000FF00) { base += 32/4; x >>= 32/4; } if (x & (unsigned) 0x000000F0) { base += 32/8; x >>= 32/8; } return base + bval[x]; } inline size_t num_digits(unsigned x) { static const unsigned powertable[] = { 0,10,100,1000,10000,100000,1000000,10000000,100000000, 1000000000 }; size_t lg_ten = msb_u32(x) * 1233 >> 12; size_t adjust = (x >= powertable[lg_ten]); return lg_ten + adjust; } #endif /* __GNUC__ */ struct CharBuffer { class reverse_iterator : public iterator { char* m_p; public: reverse_iterator(char* p) : m_p(p - 1) {} reverse_iterator operator++() { return --m_p; } reverse_iterator operator++(int) { return m_p--; } char operator*() const { return *m_p; } bool operator==( reverse_iterator it) const { return m_p == it.m_p; } bool operator!=( reverse_iterator it) const { return m_p != it.m_p; } difference_type operator-( reverse_iterator it) const { return it.m_p - m_p; } }; }; union PairTable { char c[2]; unsigned short u; } PACK table[100] ALIGN(1024) = { {{'0','0'}},{{'0','1'}},{{'0','2'}},{{'0','3'}},{{'0','4'}},{{'0','5'}},{{'0','6'}},{{'0','7'}},{{'0','8'}},{{'0','9'}}, {{'1','0'}},{{'1','1'}},{{'1','2'}},{{'1','3'}},{{'1','4'}},{{'1','5'}},{{'1','6'}},{{'1','7'}},{{'1','8'}},{{'1','9'}}, {{'2','0'}},{{'2','1'}},{{'2','2'}},{{'2','3'}},{{'2','4'}},{{'2','5'}},{{'2','6'}},{{'2','7'}},{{'2','8'}},{{'2','9'}}, {{'3','0'}},{{'3','1'}},{{'3','2'}},{{'3','3'}},{{'3','4'}},{{'3','5'}},{{'3','6'}},{{'3','7'}},{{'3','8'}},{{'3','9'}}, {{'4','0'}},{{'4','1'}},{{'4','2'}},{{'4','3'}},{{'4','4'}},{{'4','5'}},{{'4','6'}},{{'4','7'}},{{'4','8'}},{{'4','9'}}, {{'5','0'}},{{'5','1'}},{{'5','2'}},{{'5','3'}},{{'5','4'}},{{'5','5'}},{{'5','6'}},{{'5','7'}},{{'5','8'}},{{'5','9'}}, {{'6','0'}},{{'6','1'}},{{'6','2'}},{{'6','3'}},{{'6','4'}},{{'6','5'}},{{'6','6'}},{{'6','7'}},{{'6','8'}},{{'6','9'}}, {{'7','0'}},{{'7','1'}},{{'7','2'}},{{'7','3'}},{{'7','4'}},{{'7','5'}},{{'7','6'}},{{'7','7'}},{{'7','8'}},{{'7','9'}}, {{'8','0'}},{{'8','1'}},{{'8','2'}},{{'8','3'}},{{'8','4'}},{{'8','5'}},{{'8','6'}},{{'8','7'}},{{'8','8'}},{{'8','9'}}, {{'9','0'}},{{'9','1'}},{{'9','2'}},{{'9','3'}},{{'9','4'}},{{'9','5'}},{{'9','6'}},{{'9','7'}},{{'9','8'}},{{'9','9'}} }; } // namespace detail struct progress_timer { clock_t c; progress_timer() : c(clock()) {} int elapsed() { return clock() - c; } ~progress_timer() { clock_t d = clock() - c; cout << d / CLOCKS_PER_SEC << "." << (((d * 1000) / CLOCKS_PER_SEC) % 1000 / 100) << (((d * 1000) / CLOCKS_PER_SEC) % 100 / 10) << (((d * 1000) / CLOCKS_PER_SEC) % 10) << " s" << endl; } }; #ifdef HOPMAN_FAST namespace hopman_fast { static unsigned long cpu_cycles = 0; struct itostr_helper { static ALIGN(1024) unsigned out[10000]; itostr_helper() { for (int i = 0; i < 10000; i++) { unsigned v = i; char * o = (char*)(out + i); o[3] = v % 10 + '0'; o[2] = (v % 100) / 10 + '0'; o[1] = (v % 1000) / 100 + '0'; o[0] = (v % 10000) / 1000; if (o[0]) o[0] |= 0x30; else if (o[1] != '0') o[0] |= 0x20; else if (o[2] != '0') o[0] |= 0x10; else o[0] |= 0x00; } } }; unsigned itostr_helper::out[10000]; itostr_helper hlp_init; template  string_type itostr(T o) { typedef itostr_helper hlp; #ifdef RDTSC long first_clock = __rdtsc(); #endif unsigned blocks[3], *b = blocks + 2; blocks[0] = o < 0 ? ~o + 1 : o; blocks[2] = blocks[0] % 10000; blocks[0] /= 10000; blocks[2] = hlp::out[blocks[2]]; if (blocks[0]) { blocks[1] = blocks[0] % 10000; blocks[0] /= 10000; blocks[1] = hlp::out[blocks[1]]; blocks[2] |= 0x30303030; b--; } if (blocks[0]) { blocks[0] = hlp::out[blocks[0] % 10000]; blocks[1] |= 0x30303030; b--; } char* f = ((char*)b); f += 3 - (*f >> 4); char* str = (char*)blocks; if (o < 0) *--f = '-'; str += 12; #ifdef RDTSC cpu_cycles += __rdtsc() - first_clock; #endif return string_type(f, str); } unsigned long cycles() { return cpu_cycles; } void reset() { cpu_cycles = 0; } } #endif namespace ak { #ifdef AK_UNROLLED namespace unrolled { static unsigned long cpu_cycles = 0; template  class Proxy { static const size_t MaxValueSize = 16; static inline char* generate(int value, char* buffer) { union { char* pc; unsigned short* pu; } b = { buffer + MaxValueSize }; unsigned u, v = value < 0 ? unsigned(~value) + 1 : value; *--b.pu = detail::table[v % 100].u; u = v; if ((v /= 100)) { *--b.pu = detail::table[v % 100].u; u = v; if ((v /= 100)) { *--b.pu = detail::table[v % 100].u; u = v; if ((v /= 100)) { *--b.pu = detail::table[v % 100].u; u = v; if ((v /= 100)) { *--b.pu = detail::table[v % 100].u; u = v; } } } } *(b.pc -= (u >= 10)) = '-'; return b.pc + (value >= 0); } static inline char* generate(unsigned value, char* buffer) { union { char* pc; unsigned short* pu; } b = { buffer + MaxValueSize }; unsigned u, v = value; *--b.pu = detail::table[v % 100].u; u = v; if ((v /= 100)) { *--b.pu = detail::table[v % 100].u; u = v; if ((v /= 100)) { *--b.pu = detail::table[v % 100].u; u = v; if ((v /= 100)) { *--b.pu = detail::table[v % 100].u; u = v; if ((v /= 100)) { *--b.pu = detail::table[v % 100].u; u = v; } } } } return b.pc + (u < 10); } public: static inline string_type convert(value_type v) { char buf[MaxValueSize]; #ifdef RDTSC long first_clock = __rdtsc(); #endif char* p = generate(v, buf); char* e = buf + MaxValueSize; #ifdef RDTSC cpu_cycles += __rdtsc() - first_clock; #endif return string_type(p, e); } }; string_type itostr(int i) { return Proxy::convert(i); } string_type itostr(unsigned i) { return Proxy::convert(i); } unsigned long cycles() { return cpu_cycles; } void reset() { cpu_cycles = 0; } } #endif #if defined(AK_BW) namespace bw { static unsigned long cpu_cycles = 0; typedef uint64_t u_type; template  class Proxy { static inline void generate(unsigned v, size_t len, char* buffer) { u_type u = v; switch(len) { default: u = (v * 1374389535ULL) >> 37; *(uint16_t*)(buffer + 8) = detail::table[v -= 100 * u].u; case 8: v = (u * 1374389535ULL) >> 37; *(uint16_t*)(buffer + 6) = detail::table[u -= 100 * v].u; case 6: u = (v * 1374389535ULL) >> 37; *(uint16_t*)(buffer + 4) = detail::table[v -= 100 * u].u; case 4: v = (u * 167773) >> 24; *(uint16_t*)(buffer + 2) = detail::table[u -= 100 * v].u; case 2: *(uint16_t*)buffer = detail::table[v].u; case 0: return; case 9: u = (v * 1374389535ULL) >> 37; *(uint16_t*)(buffer + 7) = detail::table[v -= 100 * u].u; case 7: v = (u * 1374389535ULL) >> 37; *(uint16_t*)(buffer + 5) = detail::table[u -= 100 * v].u; case 5: u = (v * 1374389535ULL) >> 37; *(uint16_t*)(buffer + 3) = detail::table[v -= 100 * u].u; case 3: v = (u * 167773) >> 24; *(uint16_t*)(buffer + 1) = detail::table[u -= 100 * v].u; case 1: *buffer = v + 0x30; } } public: static inline string_type convert(bool neg, unsigned val) { char buf[16]; #ifdef RDTSC long first_clock = __rdtsc(); #endif size_t len = detail::num_digits(val); buf[0] = '-'; char* e = buf + neg; generate(val, len, e); e += len; #ifdef RDTSC cpu_cycles += __rdtsc() - first_clock; #endif return string_type(buf, e); } }; string_type itostr(int i) { return Proxy::convert(i < 0, i < 0 ? unsigned(~i) + 1 : i); } string_type itostr(unsigned i) { return Proxy::convert(false, i); } unsigned long cycles() { return cpu_cycles; } void reset() { cpu_cycles = 0; } } #endif #if defined(AK_FW) namespace fw { static unsigned long cpu_cycles = 0; typedef uint32_t u_type; template  class Proxy { static inline void generate(unsigned v, size_t len, char* buffer) { #if defined(__GNUC__) && defined(__x86_64__) uint16_t w; uint32_t u; __asm__ __volatile__ ( "jmp %*T%=(,%3,8) \n\t" "T%=: .quad L0%= \n\t" " .quad L1%= \n\t" " .quad L2%= \n\t" " .quad L3%= \n\t" " .quad L4%= \n\t" " .quad L5%= \n\t" " .quad L6%= \n\t" " .quad L7%= \n\t" " .quad L8%= \n\t" " .quad L9%= \n\t" " .quad L10%= \n\t" "L10%=: \n\t" " imulq $1441151881, %q0, %q1\n\t" " shrq $57, %q1 \n\t" " movw %c5(,%q1,2), %w2 \n\t" " imull $100000000, %1, %1 \n\t" " subl %1, %0 \n\t" " movw %w2, (%4) \n\t" "L8%=: \n\t" " imulq $1125899907, %q0, %q1\n\t" " shrq $50, %q1 \n\t" " movw %c5(,%q1,2), %w2 \n\t" " imull $1000000, %1, %1 \n\t" " subl %1, %0 \n\t" " movw %w2, -8(%4,%3) \n\t" "L6%=: \n\t" " imulq $429497, %q0, %q1 \n\t" " shrq $32, %q1 \n\t" " movw %c5(,%q1,2), %w2 \n\t" " imull $10000, %1, %1 \n\t" " subl %1, %0 \n\t" " movw %w2, -6(%4,%3) \n\t" "L4%=: \n\t" " imull $167773, %0, %1 \n\t" " shrl $24, %1 \n\t" " movw %c5(,%q1,2), %w2 \n\t" " imull $100, %1, %1 \n\t" " subl %1, %0 \n\t" " movw %w2, -4(%4,%3) \n\t" "L2%=: \n\t" " movw %c5(,%q0,2), %w2 \n\t" " movw %w2, -2(%4,%3) \n\t" "L0%=: jmp 1f \n\t" "L9%=: \n\t" " imulq $1801439851, %q0, %q1\n\t" " shrq $54, %q1 \n\t" " movw %c5(,%q1,2), %w2 \n\t" " imull $10000000, %1, %1 \n\t" " subl %1, %0 \n\t" " movw %w2, (%4) \n\t" "L7%=: \n\t" " imulq $43980466, %q0, %q1 \n\t" " shrq $42, %q1 \n\t" " movw %c5(,%q1,2), %w2 \n\t" " imull $100000, %1, %1 \n\t" " subl %1, %0 \n\t" " movw %w2, -7(%4,%3) \n\t" "L5%=: \n\t" " imulq $268436, %q0, %q1 \n\t" " shrq $28, %q1 \n\t" " movw %c5(,%q1,2), %w2 \n\t" " imull $1000, %1, %1 \n\t" " subl %1, %0 \n\t" " movw %w2, -5(%4,%3) \n\t" "L3%=: \n\t" " imull $6554, %0, %1 \n\t" " shrl $15, %1 \n\t" " andb $254, %b1 \n\t" " movw %c5(,%q1), %w2 \n\t" " leal (%1,%1,4), %1 \n\t" " subl %1, %0 \n\t" " movw %w2, -3(%4,%3) \n\t" "L1%=: \n\t" " addl $48, %0 \n\t" " movb %b0, -1(%4,%3) \n\t" "1: \n\t" : "+r"(v), "=&q"(u), "=&r"(w) : "r"(len), "r"(buffer), "i"(detail::table) : "memory", "cc" ); #else u_type u; switch(len) { default: u = (v * 1441151881ULL) >> 57; *(uint16_t*)(buffer) = detail::table[u].u; v -= u * 100000000; case 8: u = (v * 1125899907ULL) >> 50; *(uint16_t*)(buffer + len - 8) = detail::table[u].u; v -= u * 1000000; case 6: u = (v * 429497ULL) >> 32; *(uint16_t*)(buffer + len - 6) = detail::table[u].u; v -= u * 10000; case 4: u = (v * 167773) >> 24; *(uint16_t*)(buffer + len - 4) = detail::table[u].u; v -= u * 100; case 2: *(uint16_t*)(buffer + len - 2) = detail::table[v].u; case 0: return; case 9: u = (v * 1801439851ULL) >> 54; *(uint16_t*)(buffer) = detail::table[u].u; v -= u * 10000000; case 7: u = (v * 43980466ULL) >> 42; *(uint16_t*)(buffer + len - 7) = detail::table[u].u; v -= u * 100000; case 5: u = (v * 268436ULL) >> 28; *(uint16_t*)(buffer + len - 5) = detail::table[u].u; v -= u * 1000; case 3: u = (v * 6554) >> 16; *(uint16_t*)(buffer + len - 3) = detail::table[u].u; v -= u * 10; case 1: *(buffer + len - 1) = v + 0x30; } #endif } public: static inline string_type convert(bool neg, unsigned val) { char buf[16]; #ifdef RDTSC long first_clock = __rdtsc(); #endif size_t len = detail::num_digits(val); if (neg) buf[0] = '-'; char* e = buf + len + neg; generate(val, len, buf + neg); #ifdef RDTSC cpu_cycles += __rdtsc() - first_clock; #endif return string_type(buf, e); } }; string_type itostr(int i) { return Proxy::convert(i < 0, i < 0 ? unsigned(~i) + 1 : i); } string_type itostr(unsigned i) { return Proxy::convert(false, i); } unsigned long cycles() { return cpu_cycles; } void reset() { cpu_cycles = 0; } } #endif } // ak namespace wm { #ifdef WM_VEC #if defined(__GNUC__) && defined(__x86_64__) namespace vec { static unsigned long cpu_cycles = 0; template  class Proxy { static inline unsigned generate(unsigned v, char* buf) { static struct { unsigned short mul_10[8]; unsigned short div_const[8]; unsigned short shl_const[8]; unsigned char to_ascii[16]; } ALIGN(64) bits = { { // mul_10 10, 10, 10, 10, 10, 10, 10, 10 }, { // div_const 8389, 5243, 13108, 0x8000, 8389, 5243, 13108, 0x8000 }, { // shl_const 1 << (16 - (23 + 2 - 16)), 1 << (16 - (19 + 2 - 16)), 1 << (16 - 1 - 2), 1 << (15), 1 << (16 - (23 + 2 - 16)), 1 << (16 - (19 + 2 - 16)), 1 << (16 - 1 - 2), 1 << (15) }, { // to_ascii '0', '0', '0', '0', '0', '0', '0', '0', '0', '0', '0', '0', '0', '0', '0', '0' } }; unsigned x, y, l; x = (v * 1374389535ULL) >> 37; y = v; l = 0; if (x) { unsigned div = 0xd1b71759; unsigned mul = 55536; __m128i z, m, a, o; y -= 100 * x; z = _mm_cvtsi32_si128(x); m = _mm_load_si128((__m128i*)bits.mul_10); o = _mm_mul_epu32( z, _mm_cvtsi32_si128(div)); z = _mm_add_epi32( z, _mm_mul_epu32( _mm_cvtsi32_si128(mul), _mm_srli_epi64( o, 45) ) ); z = _mm_slli_epi64( _mm_shuffle_epi32( _mm_unpacklo_epi16(z, z), 5 ), 2 ); a = _mm_load_si128((__m128i*)bits.to_ascii); z = _mm_mulhi_epu16( _mm_mulhi_epu16( z, *(__m128i*)bits.div_const ), *(__m128i*)bits.shl_const ); z = _mm_sub_epi16( z, _mm_slli_epi64( _mm_mullo_epi16( m, z ), 16 ) ); z = _mm_add_epi8( _mm_packus_epi16( z, _mm_xor_si128(o, o) ), a ); x = __builtin_ctz( ~_mm_movemask_epi8( _mm_cmpeq_epi8( a, z ) ) ); l = 8 - x; uint64_t q = _mm_cvtsi128_si64(z) >> (x * 8); *(uint64_t*)buf = q; buf += l; x = 1; } v = (y * 6554) >> 16; l += 1 + (x | (v != 0)); *(unsigned short*)buf = 0x30 + ((l > 1) ? ((0x30 + y - v * 10) << 8) + v : y); return l; } public: static inline string_type convert(bool neg, unsigned val) { char buf[16]; #ifdef RDTSC long first_clock = __rdtsc(); #endif buf[0] = '-'; unsigned len = generate(val, buf + neg); char* e = buf + len + neg; #ifdef RDTSC cpu_cycles += __rdtsc() - first_clock; #endif return string_type(buf, e); } }; inline string_type itostr(int i) { return Proxy::convert(i < 0, i < 0 ? unsigned(~i) + 1 : i); } inline string_type itostr(unsigned i) { return Proxy::convert(false, i); } unsigned long cycles() { return cpu_cycles; } void reset() { cpu_cycles = 0; } } #endif #endif } // wm namespace tmn { #ifdef TM_CPP namespace cpp { static unsigned long cpu_cycles = 0; template  class Proxy { static inline void generate(unsigned v, char* buffer) { unsigned const f1_10000 = (1 << 28) / 10000; unsigned tmplo, tmphi; unsigned lo = v % 100000; unsigned hi = v / 100000; tmplo = lo * (f1_10000 + 1) - (lo >> 2); tmphi = hi * (f1_10000 + 1) - (hi >> 2); unsigned mask = 0x0fffffff; unsigned shift = 28; for(size_t i = 0; i < 5; i++) { buffer[i + 0] = '0' + (char)(tmphi >> shift); buffer[i + 5] = '0' + (char)(tmplo >> shift); tmphi = (tmphi & mask) * 5; tmplo = (tmplo & mask) * 5; mask >>= 1; shift--; } } public: static inline string_type convert(bool neg, unsigned val) { #ifdef RDTSC long first_clock = __rdtsc(); #endif char buf[16]; size_t len = detail::num_digits(val); char* e = buf + 11; generate(val, buf + 1); buf[10 - len] = '-'; len += neg; char* b = e - len; #ifdef RDTSC cpu_cycles += __rdtsc() - first_clock; #endif return string_type(b, e); } }; string_type itostr(int i) { return Proxy::convert(i < 0, i < 0 ? unsigned(~i) + 1 : i); } string_type itostr(unsigned i) { return Proxy::convert(false, i); } unsigned long cycles() { return cpu_cycles; } void reset() { cpu_cycles = 0; } } #endif #ifdef TM_VEC namespace vec { static unsigned long cpu_cycles = 0; template  class Proxy { static inline unsigned generate(unsigned val, char* buffer) { static struct { unsigned char mul_10[16]; unsigned char to_ascii[16]; unsigned char gather[16]; unsigned char shift[16]; } ALIGN(64) bits = { { 10,0,0,0,10,0,0,0,10,0,0,0,10,0,0,0 }, { '0','0','0','0','0','0','0','0','0','0','0','0','0','0','0','0' }, { 3,5,6,7,9,10,11,13,14,15,0,0,0,0,0,0 }, { 0,1,2,3,4,5,6,7,8,9,10,11,12,13,14,15 } }; unsigned u = val / 1000000; unsigned l = val - u * 1000000; __m128i x, h, f, m, n; n = _mm_load_si128((__m128i*)bits.mul_10); x = _mm_set_epi64x( l, u ); h = _mm_mul_epu32( x, _mm_set1_epi32(4294968) ); x = _mm_sub_epi64( x, _mm_srli_epi64( _mm_mullo_epi32( h, _mm_set1_epi32(1000) ), 32 ) ); f = _mm_set1_epi32((1 << 28) / 1000 + 1); m = _mm_srli_epi32( _mm_cmpeq_epi32(m, m), 4 ); x = _mm_shuffle_epi32( _mm_blend_epi16( x, h, 204 ), 177 ); f = _mm_sub_epi32( _mm_mullo_epi32(f, x), _mm_srli_epi32(x, 2) ); h = _mm_load_si128((__m128i*)bits.to_ascii); x = _mm_srli_epi32(f, 28); f = _mm_mullo_epi32( _mm_and_si128( f, m ), n ); x = _mm_or_si128( x, _mm_slli_epi32(_mm_srli_epi32(f, 28), 8) ); f = _mm_mullo_epi32( _mm_and_si128( f, m ), n ); x = _mm_or_si128( x, _mm_slli_epi32(_mm_srli_epi32(f, 28), 16) ); f = _mm_mullo_epi32( _mm_and_si128( f, m ), n ); x = _mm_or_si128( x, _mm_slli_epi32(_mm_srli_epi32(f, 28), 24) ); x = _mm_add_epi8( _mm_shuffle_epi8(x, *(__m128i*)bits.gather), h ); l = __builtin_ctz( ~_mm_movemask_epi8( _mm_cmpeq_epi8( h, x ) ) | (1 << 9) ); x = _mm_shuffle_epi8( x, _mm_add_epi8(*(__m128i*)bits.shift, _mm_set1_epi8(l) ) ); _mm_store_si128( (__m128i*)buffer, x ); return 10 - l; } public: static inline string_type convert(bool neg, unsigned val) { #ifdef RDTSC long first_clock = __rdtsc(); #endif char arena[32]; char* buf = (char*)((uintptr_t)(arena + 16) & ~(uintptr_t)0xf); *(buf - 1)= '-'; unsigned len = generate(val, buf) + neg; buf -= neg; char* end = buf + len; #ifdef RDTSC cpu_cycles += __rdtsc() - first_clock; #endif return string_type(buf, end); } }; string_type itostr(int i) { return Proxy::convert(i < 0, i < 0 ? unsigned(~i) + 1 : i); } string_type itostr(unsigned i) { return Proxy::convert(false, i); } unsigned long cycles() { return cpu_cycles; } void reset() { cpu_cycles = 0; } } #endif } bool fail(string in, string_type out) { cout << "failure: " << in << " => " << out << endl; return false; } #define TEST(x, n) \ stringstream ss; \ string_type s = n::itostr(x); \ ss << (long long)x; \ if (::strcmp(ss.str().c_str(), s.c_str())) { \ passed = fail(ss.str(), s); \ break; \ } #define test(x) { \ passed = true; \ if (0 && passed) { \ char c = CHAR_MIN; \ do { \ TEST(c, x); \ } while (c++ != CHAR_MAX); \ if (!passed) cout << #x << " failed char!!!" << endl; \ } \ if (0 && passed) { \ short c = numeric_limits::min(); \ do { \ TEST(c, x); \ } while (c++ != numeric_limits::max()); \ if (!passed) cout << #x << " failed short!!!" << endl; \ } \ if (passed) { \ int c = numeric_limits::min(); \ do { \ TEST(c, x); \ } while ((c += 100000) < numeric_limits::max() - 100000); \ if (!passed) cout << #x << " failed int!!!" << endl; \ } \ if (passed) { \ unsigned c = numeric_limits::max(); \ do { \ TEST(c, x); \ } while ((c -= 100000) > 100000); \ if (!passed) cout << #x << " failed unsigned int!!!" << endl; \ } \ } #define time(x, N) \ if (passed) { \ static const int64_t limits[] = \ {0, 10, 100, 1000, 10000, 100000, \ 1000000, 10000000, 100000000, 1000000000, 10000000000ULL }; \ long passes = 0; \ cout << #x << ": "; \ progress_timer t; \ uint64_t s = 0; \ if (do_time) { \ for (int n = 0; n < N1; n++) { \ int i = 0; \ while (i < N2) { \ int v = ((NM - i) % limits[N]) | (limits[N] / 10); \ int w = x::itostr(v).size() + \ x::itostr(-v).size(); \ i += w * mult; \ passes++; \ } \ s += i / mult; \ } \ } \ k += s; \ cout << N << " digits: " \ << s / double(t.elapsed()) * CLOCKS_PER_SEC/1000000 << " MB/sec, " << (x::cycles() / passes >> 1) << " clocks per pass "; \ x::reset(); \ } #define series(n) \ { if (do_test) test(n); if (do_time) time(n, 1); if (do_time) time(n, 2); \ if (do_time) time(n, 3); if (do_time) time(n, 4); if (do_time) time(n, 5); \ if (do_time) time(n, 6); if (do_time) time(n, 7); if (do_time) time(n, 8); \ if (do_time) time(n, 9); if (do_time) time(n, 10); } int N1 = 1, N2 = 500000000, NM = INT_MAX; int mult = 1; // used to stay under timelimit on ideone unsigned long long k = 0; int main(int argc, char** argv) { bool do_time = 1, do_test = 1; bool passed = true; #ifdef HOPMAN_FAST series(hopman_fast) #endif #ifdef WM_VEC series(wm::vec) #endif #ifdef TM_CPP series(tmn::cpp) #endif #ifdef TM_VEC series(tmn::vec) #endif #ifdef AK_UNROLLED series(ak::unrolled) #endif #if defined(AK_BW) series(ak::bw) #endif #if defined(AK_FW) series(ak::fw) #endif return k; } 

Here’s my little attempt of this fun puzzle.

Instead of using lookup tables, I wanted the compiler to figure it all out. In this case in particular – if you read Hackers’ Delight, you see how divide and modulo work — which makes it very possible to optimize that using SSE/AVX instructions.

Performance benchmark

As for speed, my benchmark here tells me it’s 1,5 times faster than the work of Timo (on my Intel Haswell it runs on approximately 1 GB/s).

Things you could consider a cheat

As for the not-making-a-std-string cheat that I use — of course I took that into consideration for my benchmark of Timo’s method as well.

I do use an intrinsic: BSR. If you like, you can also use DeBruijn tables instead – which is one of the things I wrote quite a bit about on my ‘fastest 2log’ post. Of course, this does have a performance penalty (*well… if you’re doing a lot of itoa operations you can actually make a faster BSR but I guess that’s not fair…).

The way it works

First thing to do is figure out how much memory we need. This is basically a 10log, which can be implemented in a number of smart ways. See the frequently quoted ” Bit Twiddling Hacks ” for details.

Next thing to do is to execute the numeric output. I use template recursion for this, so the compiler will figure it out.

I use ‘modulo’ and ‘div’ right next to each other. If you read Hacker’s Delight, you will notice that the two are closely related, so if you have one answer, you probably have the other as well. I figured the compiler can figure out the details… 🙂

El código

Getting the number of digits using a (modified) log10:

 struct logarithm { static inline int log2(unsigned int value) { unsigned long index; if (!_BitScanReverse(&index, value)) { return 0; } // add 1 if x is NOT a power of 2 (to do the ceil) return index + (value&(value - 1) ? 1 : 0); } static inline int numberDigits(unsigned int v) { static unsigned int const PowersOf10[] = { 0, 10, 100, 1000, 10000, 100000, 1000000, 10000000, 100000000, 1000000000 }; int t = (logarithm::log2(v) + 1) * 1233 >> 12; // (use a lg2 method from above) return 1 + t - (v < PowersOf10[t]); } }; 

Getting yourself the string:

 template  struct WriteHelper { inline static void WriteChar(char* buf, unsigned int value) { unsigned int div = value / 10; unsigned int rem = value % 10; buf[count - 1] = rem + '0'; WriteHelper::WriteChar(buf, div); } }; template <> struct WriteHelper<1> { inline static void WriteChar(char* buf, unsigned int value) { buf[0] = '0' + value; } }; // Boring code that converts a length into a switch. // TODO: Test if recursion with an 'if' is faster. static inline void WriteNumber(char* data, int len, unsigned int val) { switch (len) { case 1: WriteHelper<1>::WriteChar(data, static_cast(val)); break; case 2: WriteHelper<2>::WriteChar(data, static_cast(val)); break; case 3: WriteHelper<3>::WriteChar(data, static_cast(val)); break; case 4: WriteHelper<4>::WriteChar(data, static_cast(val)); break; case 5: WriteHelper<5>::WriteChar(data, static_cast(val)); break; case 6: WriteHelper<6>::WriteChar(data, static_cast(val)); break; case 7: WriteHelper<7>::WriteChar(data, static_cast(val)); break; case 8: WriteHelper<8>::WriteChar(data, static_cast(val)); break; case 9: WriteHelper<9>::WriteChar(data, static_cast(val)); break; case 10: WriteHelper<10>::WriteChar(data, static_cast(val)); break; } } // The main method you want to call... static int Write(char* data, int val) { int len; if (val >= 0) { len = logarithm::numberDigits(val); WriteNumber(data, len, unsigned int(val)); return len; } else { unsigned int v(-val); len = logarithm::numberDigits(v); WriteNumber(data+1, len, v); data[0] = '-'; return len + 1; } } 

I believe I have created the fastest integer-to-string algorithm. It’s a variation of the Modulo 100 algorithm that is about 33% faster, and most importantly it’s faster for both smaller and large numbers. It’s called the Script ItoS Algorithm. To read the paper that explains how I engineered the algorithm @see https://github.com/kabuki-starship/kabuki-toolkit/wiki/Engineering-a-Faster-Integer-to-String-Algorithm . You may use the algorithm but please think about contributing back to the Kabuki VM and check out Script ; especially if you’re interested in AMIL-NLP and/or software-defined networking protocols.

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 /** Kabuki Toolkit @version 0.x @file ~/source/crabs/print_itos.cc @author Cale McCollough  @license Copyright (C) 2017-2018 Cale McCollough ; All right reserved (R). Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except in compliance with the License. You may obtain a copy of the License [here](http://www.apache.org/licenses/LICENSE-2.0). Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for the specific language governing permissions and limitations under the License. */ #include  #include "print_itos.h" #if MAJOR_SEAM >= 1 && MINOR_SEAM >= 1 #if MAJOR_SEAM == 1 && MINOR_SEAM == 1 #define DEBUG 1 #define PRINTF(format, ...) printf(format, __VA_ARGS__); #define PUTCHAR(c) putchar(c); #define PRINT_PRINTED\ sprintf_s (buffer, 24, "%u", value); *text_end = 0;\ printf ("\n Printed \"%s\" leaving value:\"%s\":%u",\ begin, buffer, (uint)strlen (buffer)); #define PRINT_BINARY PrintBinary (value); #define PRINT_BINARY_TABLE PrintBinaryTable (value); #else #define PRINTF(x, ...) #define PUTCHAR(c) #define PRINT_PRINTED #define PRINT_BINARY #define PRINT_BINARY_TABLE #endif namespace _ { void PrintLine (char c) { std::cout << '\n'; for (int i = 80; i > 0; --i) std::cout << c; } char* Print (uint32_t value, char* text, char* text_end) { // Lookup table for powers of 10. static const uint32_t k10ToThe[]{ 1, 10, 100, 1000, 10000, 100000, 1000000, 10000000, 100000000, 1000000000, ~(uint32_t)0 }; /** Lookup table of ASCII char pairs for 00, 01, ..., 99. To convert this algorithm to big-endian, flip the digit pair bytes. */ static const uint16_t kDigits00To99[100] = { 0x3030, 0x3130, 0x3230, 0x3330, 0x3430, 0x3530, 0x3630, 0x3730, 0x3830, 0x3930, 0x3031, 0x3131, 0x3231, 0x3331, 0x3431, 0x3531, 0x3631, 0x3731, 0x3831, 0x3931, 0x3032, 0x3132, 0x3232, 0x3332, 0x3432, 0x3532, 0x3632, 0x3732, 0x3832, 0x3932, 0x3033, 0x3133, 0x3233, 0x3333, 0x3433, 0x3533, 0x3633, 0x3733, 0x3833, 0x3933, 0x3034, 0x3134, 0x3234, 0x3334, 0x3434, 0x3534, 0x3634, 0x3734, 0x3834, 0x3934, 0x3035, 0x3135, 0x3235, 0x3335, 0x3435, 0x3535, 0x3635, 0x3735, 0x3835, 0x3935, 0x3036, 0x3136, 0x3236, 0x3336, 0x3436, 0x3536, 0x3636, 0x3736, 0x3836, 0x3936, 0x3037, 0x3137, 0x3237, 0x3337, 0x3437, 0x3537, 0x3637, 0x3737, 0x3837, 0x3937, 0x3038, 0x3138, 0x3238, 0x3338, 0x3438, 0x3538, 0x3638, 0x3738, 0x3838, 0x3938, 0x3039, 0x3139, 0x3239, 0x3339, 0x3439, 0x3539, 0x3639, 0x3739, 0x3839, 0x3939, }; static const char kMsbShift[] = { 4, 7, 11, 14, 17, 21, 24, 27, 30, }; if (!text) { return nullptr; } if (text >= text_end) { return nullptr; } uint16_t* text16; char digit; uint32_t scalar; uint16_t digits1and2, digits3and4, digits5and6, digits7and8; uint32_t comparator; #if MAJOR_SEAM == 1 && MINOR_SEAM == 1 // Write a bunches of xxxxxx to the buffer for debug purposes. for (int i = 0; i <= 21; ++i) { *(text + i) = 'x'; } *(text + 21) = 0; char* begin = text; char buffer[256]; #endif if (value < 10) { PRINTF ("\n Range:[0, 9] length:1 ") if (text + 1 >= text_end) { return nullptr; } *text++ = '0' + (char)value; PRINT_PRINTED return text; } if (value < 100) { PRINTF ("\n Range:[10, 99] length:2 ") if (text + 2 >= text_end) { return nullptr; } *reinterpret_cast (text) = kDigits00To99[value]; PRINT_PRINTED return text + 2; } if (value >> 14) { if (value >> 27) { if (value >> 30) { PRINTF ("\n Range:[1073741824, 4294967295] length:10") Print10: if (text + 10 >= text_end) { return nullptr; } comparator = 100000000; digits1and2 = (uint16_t)(value / comparator); PRINTF ("\n digits1and2:%u", digits1and2) value -= digits1and2 * comparator; *reinterpret_cast (text) = kDigits00To99[digits1and2]; PRINT_PRINTED text += 2; goto Print8; } else { comparator = 1000000000; if (value >= comparator) { PRINTF ("\n Range:[100000000, 1073741823] length:10") goto Print10; } PRINTF ("\n Range:[134217727, 999999999] length:9") if (text + 9 >= text_end) { return nullptr; } comparator = 100000000; digit = (char)(value / comparator); *text++ = digit + '0'; PRINT_PRINTED value -= comparator * digit; goto Print8; } } else if (value >> 24) { comparator = k10ToThe[8]; if (value >= comparator) { PRINTF ("\n Range:[100000000, 134217728] length:9") if (text + 9 >= text_end) { return nullptr; } *text++ = '1'; PRINT_PRINTED value -= comparator; } PRINTF ("\n Range:[16777216, 9999999] length:8") if (text + 8 >= text_end) { return nullptr; } Print8: PRINTF ("\n Print8:") scalar = 10000; digits5and6 = (uint16_t)(value / scalar); digits1and2 = value - scalar * digits5and6; digits7and8 = digits5and6 / 100; digits3and4 = digits1and2 / 100; digits5and6 -= 100 * digits7and8; digits1and2 -= 100 * digits3and4; *reinterpret_cast (text + 6) = kDigits00To99[digits1and2]; PRINT_PRINTED *reinterpret_cast (text + 4) = kDigits00To99[digits3and4]; PRINT_PRINTED *reinterpret_cast (text + 2) = kDigits00To99[digits5and6]; PRINT_PRINTED *reinterpret_cast (text) = kDigits00To99[digits7and8]; PRINT_PRINTED return text + 8; } else if (value >> 20) { comparator = 10000000; if (value >= comparator) { PRINTF ("\n Range:[10000000, 16777215] length:8") if (text + 8 >= text_end) { return nullptr; } *text++ = '1'; PRINT_PRINTED value -= comparator; } else { PRINTF ("\n Range:[1048576, 9999999] length:7") if (text + 7 >= text_end) { return nullptr; } } scalar = 10000; digits5and6 = (uint16_t)(value / scalar); digits1and2 = value - scalar * digits5and6; digits7and8 = digits5and6 / 100; digits3and4 = digits1and2 / 100; digits5and6 -= 100 * digits7and8; digits1and2 -= 100 * digits3and4;; *reinterpret_cast (text + 5) = kDigits00To99[digits1and2]; PRINT_PRINTED *reinterpret_cast (text + 3) = kDigits00To99[digits3and4]; PRINT_PRINTED *reinterpret_cast (text + 1) = kDigits00To99[digits5and6]; PRINT_PRINTED *text = (char)digits7and8 + '0'; return text + 7; } else if (value >> 17) { comparator = 1000000; if (value >= comparator) { PRINTF ("\n Range:[100000, 1048575] length:7") if (text + 7 >= text_end) { return nullptr; } *text++ = '1'; PRINT_PRINTED value -= comparator; } else { PRINTF ("\n Range:[131072, 999999] length:6") if (text + 6 >= text_end) { return nullptr; } } Print6: scalar = 10000; digits5and6 = (uint16_t)(value / scalar); digits1and2 = value - scalar * digits5and6; digits7and8 = digits5and6 / 100; digits3and4 = digits1and2 / 100; digits5and6 -= 100 * digits7and8; digits1and2 -= 100 * digits3and4; text16 = reinterpret_cast (text + 6); *reinterpret_cast (text + 4) = kDigits00To99[digits1and2]; PRINT_PRINTED *reinterpret_cast (text + 2) = kDigits00To99[digits3and4]; PRINT_PRINTED *reinterpret_cast (text ) = kDigits00To99[digits5and6]; PRINT_PRINTED return text + 6; } else { // (value >> 14) if (value >= 100000) { PRINTF ("\n Range:[65536, 131071] length:6") goto Print6; } PRINTF ("\n Range:[10000, 65535] length:5") if (text + 5 >= text_end) { return nullptr; } digits5and6 = 10000; digit = (uint8_t)(value / digits5and6); value -= digits5and6 * digit; *text = digit + '0'; PRINT_PRINTED digits1and2 = (uint16_t)value; digits5and6 = 100; digits3and4 = digits1and2 / digits5and6; digits1and2 -= digits3and4 * digits5and6; *reinterpret_cast (text + 1) = kDigits00To99[digits3and4]; PRINT_PRINTED PRINTF ("\n digits1and2:%u", digits1and2) *reinterpret_cast (text + 3) = kDigits00To99[digits1and2]; PRINT_PRINTED return text + 5; } } digits1and2 = (uint16_t)value; if (value >> 10) { digits5and6 = 10000; if (digits1and2 >= digits5and6) { if (text + 5 >= text_end) { return nullptr; } PRINTF ("\n Range:[10000, 16383] length:5") *text++ = '1'; PRINT_PRINTED digits1and2 -= digits5and6; } else { PRINTF ("\n Range:[1024, 9999] length:4") if (text + 4 >= text_end) { return nullptr; } } digits5and6 = 100; digits3and4 = digits1and2 / digits5and6; digits1and2 -= digits3and4 * digits5and6; *reinterpret_cast (text ) = kDigits00To99[digits3and4]; PRINT_PRINTED *reinterpret_cast (text + 2) = kDigits00To99[digits1and2]; PRINT_PRINTED return text + 4; } else { if (text + 4 >= text_end) { return nullptr; } digits3and4 = 1000; if (digits1and2 >= digits3and4) { PRINTF ("\n Range:[1000, 1023] length:4") digits1and2 -= digits3and4; text16 = reinterpret_cast (text + 2); *text16-- = kDigits00To99[digits1and2]; PRINT_PRINTED *text16 = (((uint16_t)'1') | (((uint16_t)'0') << 8)); PRINT_PRINTED return text + 4; } PRINTF ("\n Range:[100, 999] length:3") digits1and2 = (uint16_t)value; digits3and4 = 100; digit = (char)(digits1and2 / digits3and4); digits1and2 -= digit * digits3and4; *text = digit + '0'; PRINT_PRINTED *reinterpret_cast (text + 1) = kDigits00To99[digits1and2]; PRINT_PRINTED return text + 3; } } } //< namespace _ #undef PRINTF #undef PRINT_PRINTED #endif //< MAJOR_SEAM >= 1 && MINOR_SEAM >= 1 

Autor

  • Cale McCollough

Modification to user434507’s solution. Modified to use character array instead of C++ string. Runs a bit faster. Also moved the check for 0 lower in the code…as this never happens for my particular case. Move it back if it’s more common for your case.

 // Int2Str.cpp : Defines the entry point for the console application. // #include  #include  #include "StopWatch.h" using namespace std; const char digit_pairs[201] = { "00010203040506070809" "10111213141516171819" "20212223242526272829" "30313233343536373839" "40414243444546474849" "50515253545556575859" "60616263646566676869" "70717273747576777879" "80818283848586878889" "90919293949596979899" }; void itostr(int n, char* c) { int sign = -(n<0); unsigned int val = (n^sign)-sign; int size; if(val>=10000) { if(val>=10000000) { if(val>=1000000000) { size=10; } else if(val>=100000000) { size=9; } else size=8; } else { if(val>=1000000) { size=7; } else if(val>=100000) { size=6; } else size=5; } } else { if(val>=100) { if(val>=1000) { size=4; } else size=3; } else { if(val>=10) { size=2; } else if(n==0) { c[0]='0'; c[1] = '\0'; return; } else size=1; } } size -= sign; if(sign) *c='-'; c += size-1; while(val>=100) { int pos = val % 100; val /= 100; *(short*)(c-1)=*(short*)(digit_pairs+2*pos); c-=2; } while(val>0) { *c--='0' + (val % 10); val /= 10; } c[size+1] = '\0'; } void itostr(unsigned val, char* c) { int size; if(val>=10000) { if(val>=10000000) { if(val>=1000000000) size=10; else if(val>=100000000) size=9; else size=8; } else { if(val>=1000000) size=7; else if(val>=100000) size=6; else size=5; } } else { if(val>=100) { if(val>=1000) size=4; else size=3; } else { if(val>=10) size=2; else if (val==0) { c[0]='0'; c[1] = '\0'; return; } else size=1; } } c += size-1; while(val>=100) { int pos = val % 100; val /= 100; *(short*)(c-1)=*(short*)(digit_pairs+2*pos); c-=2; } while(val>0) { *c--='0' + (val % 10); val /= 10; } c[size+1] = '\0'; } void test() { bool foundmismatch = false; char str[16]; char compare[16]; for(int i = -1000000; i < 1000000; i++) { int random = rand(); itostr(random, str); itoa(random, compare, 10); if(strcmp(str, compare) != 0) { cout << "Mismatch found: " << endl; cout << "Generated: " << str << endl; cout << "Reference: " << compare << endl; foundmismatch = true; } } if(!foundmismatch) { cout << "No mismatch found!" << endl; } cin.get(); } void benchmark() { StopWatch stopwatch; stopwatch.setup("Timer"); stopwatch.reset(); stopwatch.start(); char str[16]; for(unsigned int i = 0; i < 2000000; i++) { itostr(i, str); } stopwatch.stop(); cin.get(); } int main( int argc, const char* argv[]) { benchmark(); } 

We use the following code (for MSVC):

Templated tBitScanReverse:

 #include  namespace intrin { #pragma intrinsic(_BitScanReverse) #pragma intrinsic(_BitScanReverse64) template __forceinline auto tBitScanReverse(DWORD * out_index, TIntegerValue mask) -> std::enable_if_t<(std::is_integral::value && sizeof(TIntegerValue) == 4), unsigned char> { return _BitScanReverse(out_index, mask); } template __forceinline auto tBitScanReverse(DWORD * out_index, TIntegerValue mask) -> std::enable_if_t<(std::is_integral::value && sizeof(TIntegerValue) == 8), unsigned char> { #if !(_M_IA64 || _M_AMD64) auto res = _BitScanReverse(out_index, (unsigned long)(mask >> 32)); if (res) { out_index += 32; return res; } return _BitScanReverse(out_index, (unsigned long)mask); #else return _BitScanReverse64(out_index, mask); #endif } } 

char/wchar_t helpers:

 template inline constexpr TChar ascii_0(); template<> inline constexpr char ascii_0() { return '0'; } template<> inline constexpr wchar_t ascii_0() { return L'0'; } template inline constexpr TChar ascii_DEC(TInt d) { return (TChar)(ascii_0() + d); } 

Powers of 10 tables:

 static uint32 uint32_powers10[] = { 1, 10, 100, 1000, 10000, 100000, 1000000, 10000000, 100000000, 1000000000 // 123456789 }; static uint64 uint64_powers10[] = { 1ULL, 10ULL, 100ULL, 1000ULL, 10000ULL, 100000ULL, 1000000ULL, 10000000ULL, 100000000ULL, 1000000000ULL, 10000000000ULL, 100000000000ULL, 1000000000000ULL, 10000000000000ULL, 100000000000000ULL, 1000000000000000ULL, 10000000000000000ULL, 100000000000000000ULL, 1000000000000000000ULL, 10000000000000000000ULL // 1234567890123456789 }; template inline constexpr const TUint * powers10(); template<> inline constexpr const uint32 * powers10() { return uint32_powers10; } template<> inline constexpr const uint64 * powers10() { return uint64_powers10; } 

Actual print:

 template __forceinline auto print_dec( TUInt u, TChar * & buffer) -> typename std::enable_if_t::value> { if (u < 10) { // 1-digit, including 0 *buffer++ = ascii_DEC(u); } else { DWORD log2u; intrin::tBitScanReverse(&log2u, u); // log2u [3,31] (u >= 10) DWORD log10u = ((log2u + 1) * 77) >> 8; // log10u [1,9] 77/256 = ln(2) / ln(10) DWORD digits = log10u + (u >= powers10()[log10u]); // digits [2,10] buffer += digits; auto p = buffer; for (--digits; digits; --digits) { auto x = u / 10, d = u - x * 10; *--p = ascii_DEC(d); u = x; } *--p = ascii_DEC(u); } } 

Last loop can be unrolled:

 switch (digits) { case 10: { auto x = u / 10, d = u - x * 10; *--p = ascii_DEC(d); u = x; } case 9: { auto x = u / 10, d = u - x * 10; *--p = ascii_DEC(d); u = x; } case 8: { auto x = u / 10, d = u - x * 10; *--p = ascii_DEC(d); u = x; } case 7: { auto x = u / 10, d = u - x * 10; *--p = ascii_DEC(d); u = x; } case 6: { auto x = u / 10, d = u - x * 10; *--p = ascii_DEC(d); u = x; } case 5: { auto x = u / 10, d = u - x * 10; *--p = ascii_DEC(d); u = x; } case 4: { auto x = u / 10, d = u - x * 10; *--p = ascii_DEC(d); u = x; } case 3: { auto x = u / 10, d = u - x * 10; *--p = ascii_DEC(d); u = x; } case 2: { auto x = u / 10, d = u - x * 10; *--p = ascii_DEC(d); u = x; *--p = ascii_DEC(u); break; } default: __assume(0); } 

The main idea is the same as @atlaste suggested before: https://stackoverflow.com/a/29039967/2204001

Why is nobody using the div function from stdlib when both, quotient and remainder are needed?
Using Timo’s source code, I ended up with something like this:

 if(val >= 0) { div_t d2 = div(val,100); while(d2.quot) { COPYPAIR(it,2 * d2.rem); it-=2; d2 = div(d2.quot,100); } COPYPAIR(it,2*d2.rem); if(d2.quot<10) it++; } else { div_t d2 = div(val,100); while(d2.quot) { COPYPAIR(it,-2 * d2.rem); it-=2; d2 = div(d2.quot,100); } COPYPAIR(it,-2*d2.rem); if(d2.quot<=-10) it--; *it = '-'; } 

Ok, for unsigned int's, the div function can't be used but unsigned's can be handled separate.
I've defined the COPYPAIR macro as follows to test variations how to copy the 2 characters from the digit_pairs (found no obvious advantage of any of these methods):

 #define COPYPAIR0(_p,_i) { memcpy((_p), &digit_pairs[(_i)], 2); } #define COPYPAIR1(_p,_i) { (_p)[0] = digit_pairs[(_i)]; (_p)[1] = digit_pairs[(_i)+1]; } #define COPYPAIR2(_p,_i) { unsigned short * d = (unsigned short *)(_p); unsigned short * s = (unsigned short *)&digit_pairs[(_i)]; *d = *s; } #define COPYPAIR COPYPAIR2