examples/compare_test.c

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

#include "xdelta3.h"

#define NUM (1<<20)
#define ITERS 100

/* From wikipedia on RDTSC */
inline uint64_t rdtsc() {
  uint32_t lo, hi;
  asm volatile ("rdtsc" : "=a" (lo), "=d" (hi));
  return (uint64_t)hi << 32 | lo;
}

typedef int (*test_func)(const char *s1, const char *s2, int n);

void run_test(const char *buf1, const char *buf2,
	      const char *name, test_func func) {
  uint64_t start, end;
  uint64_t accum = 0;
  int i, x;

  for (i = 0; i < ITERS; i++) {
    start = rdtsc();
    x = func(buf1, buf2, NUM);
    end = rdtsc();
    accum += end - start;
    assert(x == NUM - 1);
  }

  accum /= ITERS;

  printf("%s : %qu cycles\n", name, accum);
}

/* Build w/ -fno-builtin for this to be fast, this assumes that there
 * is a difference at s1[n-1] */
int memcmp_fake(const char *s1, const char *s2, int n) {
  int x = memcmp(s1, s2, n);
  return x < 0 ? n - 1 : n + 1;
}

#define UNALIGNED_OK 1
static inline int
test2(const char *s1c, const char *s2c, int n)
{
  int i = 0;
#if UNALIGNED_OK
  int nint = n / sizeof(int);

  if (nint >> 3)
    {
      int j = 0;
      const int *s1 = (const int*)s1c;
      const int *s2 = (const int*)s2c;
      int nint_8 = nint - 8;

      while (i <= nint_8 &&
	     s1[i++] == s2[j++] &&
	     s1[i++] == s2[j++] &&
	     s1[i++] == s2[j++] &&
	     s1[i++] == s2[j++] &&
	     s1[i++] == s2[j++] &&
	     s1[i++] == s2[j++] &&
	     s1[i++] == s2[j++] &&	 
	     s1[i++] == s2[j++]) { }

      i = (i - 1) * sizeof(int);
    }
#endif

  while (i < n && s1c[i] == s2c[i])
    {
      i++;
    }
  return i;
}

static inline int
test1(const char *s1c, const char *s2c, int n) {
  int i = 0;
  while (i < n && s1c[i] == s2c[i])
    {
      i++;
    }
  return i;
}

int main(/*int argc, char **argv*/) {
  char *buf1 = malloc(NUM+1);
  char *buf2 = malloc(NUM+1);
  int i;

  for (i = 0; i < NUM; i++) {
    buf1[i] = buf2[i] = rand();
  }

  buf2[NUM-1]++;

  printf ("ALIGNED\n");

  run_test(buf1, buf2, "memcmp", &memcmp_fake);
  run_test(buf1, buf2, "test1", &test1);
  run_test(buf1, buf2, "test2", &test2);

  for (i = 0; i < NUM; i++) {
    buf1[i] = buf2[i+1] = rand();
  }

  buf2[NUM]++;

  printf ("UNALIGNED\n");

  run_test(buf1, buf2+1, "memcmp", &memcmp_fake);
  run_test(buf1, buf2+1, "test1", &test1);
  run_test(buf1, buf2+1, "test2", &test2);

  return 0;
}