benchmark-xor.c

#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#include <inttypes.h>
#include <sys/errno.h>
#include <sys/time.h>

#define die(errnum) { errno = errnum; perror(""); exit(1); }

#define xor(rounds) { \
  bench(); \
  for (r = 0; r < rounds; ++r)  \
    for (i = 0; i < len_str; ++i)  \
      pos = i % len_key, str[i] ^= key[pos]; \
  benched = bench(); \
  printf("%-8d rounds:\t%1.8f\n", rounds, benched);\
}

double bench();

int main(int argc, char **argv, char **envp) 
{
  uint_fast8_t len_key, len_str, i, pos;
  uint_fast32_t r;
  char *key, *str;
  double benched;

  if (argc != 3) {
    die(EINVAL);
  }
  key = argv[1];
  str = argv[2]; 
  len_key = strlen(key), len_str = strlen(str);
  if (len_key < 1 || len_str < 1) {
    die(EINVAL);
  }
  xor(1);
  xor(10);
  xor(100);
  xor(1000);
  xor(10000);
  xor(100000);
  xor(1000000);
  xor(10000000);

}

double bench() {
    static struct timeval t = { 0, 0 }, z = { 0, 0};
    double result;
    if (t.tv_sec == 0) {
      gettimeofday(&t, NULL);
      return 0.0;
    }
    gettimeofday(&z, NULL);
    result = z.tv_sec - t.tv_sec;
    result += (z.tv_usec - t.tv_usec) / 1000000.0;
    t.tv_sec = 0;
    return result;
}

~
$ gcc -O3 benchmark-xor.c

~
$ ./a.out KEY 'some string'
1        rounds:	0.00000000
10       rounds:	0.00000000
100      rounds:	0.00000600
1000     rounds:	0.00004500
10000    rounds:	0.00057400
100000   rounds:	0.00457000
1000000  rounds:	0.04780900
10000000 rounds:	0.41665100

~
$ ./a.out KEY 'some stupidly long boring oddball string that never really ends'
1        rounds:	0.00000000
10       rounds:	0.00000300
100      rounds:	0.00002800
1000     rounds:	0.00027800
10000    rounds:	0.00290900
100000   rounds:	0.02388100
1000000  rounds:	0.26921400
10000000 rounds:	2.40639700