memset

memset.c

#include <stdio.h>
#include <stdlib.h>
#include <time.h>

void* memset1(void* mem, int value, size_t num) {
  char* m = mem;
  char v = value;
  while (num-- != 0)
    *(m + num) = v;
  return mem;
}

void* memset2(void* mem, int value, size_t num) {
  int* m = mem;
  char c;
  char* mc;

  for (; num >= 4; num -= 4)
    *(m + num) = value;
  if (num != 0) {
    c = value;
    mc = m + num;
    while (num--)
      *(mc + num) = 0;
  }
  return mem;
}    

void* memset_sse(void* mem, int value, size_t num) {
  value = value | (value << 8);
  for (; num >= 16; num -= 16) {
    asm(
      "movd %0, %%xmm0    \n\t"
      "movdqu   %%xmm0, 0(%1) \n\t"
    : : "r" (value), "r" (mem));
    }
}

void* memset_asm(void* ptr, int value, size_t num) {
  asm("rep stosl;" : : "a"(value | (value << 8) | (value << 16) | (value << 24)), "D" ((size_t) ptr), "c" (num / 4));
  asm("rep stosb;" : : "a"(value), "D" (((size_t) ptr) + ((num / 4) * 4)),
     "c" (num - ((num / 4) * 4)));
     }

int main(int argc, char** argv) {
  unsigned int i, e = 1024, sz = 1024 * 1024;
  clock_t start, stop;
  char* mem = (char*) malloc(sz);
  start = clock();
  for (i = 0; i < e; i++) {
    memset(mem, 64, sz);
  }
  stop = clock();
  printf("Standard memset: %f\n", ((double) stop - start) / CLOCKS_PER_SEC);

memset(mem, 0, sz);

  start = clock();
  for (i = 0; i < e; i++) {
    memset1(mem, 61, sz);
  }
  stop = clock();
  printf("Int memset: %f\n", ((double) stop - start) / CLOCKS_PER_SEC);

  for (i = 0; i < sz; i++) {
    if (*(mem + i) != 61) {
      printf("Failed at %i!\n", i);
      break;
      }
  }
  
  memset(mem, 0, sz);
  
  start = clock();
  for (i = 0; i < e; i++) {
    memset_asm(mem, 61, sz);
  }
  stop = clock();
  printf("SSE memset: %f\n", ((double) stop - start) / CLOCKS_PER_SEC);

  for (i = 0; i < sz; i++) {
    if (*(mem + i) != 61) {
      printf("Failed at %i (%x)!\n", i, *(mem + i));
      break;
      }
  }
  return 0;
}