SYNTHETIC BENCHMARKS ARE HARD LET'S GO SHOPPING

bench.c

#include <stdio.h>
#include <stdlib.h>
#include <stdint.h>
#include <sys/time.h>
#include <sys/resource.h>

static double get_time()
{
    struct timeval t;
    struct timezone tzp;
    gettimeofday(&t, &tzp);
    return t.tv_sec + t.tv_usec*1e-6;
}

#define GIT_OID_RAWSZ 20

typedef struct _git_oid git_oid;
struct _git_oid {
	/** raw binary formatted id */
	unsigned char id[GIT_OID_RAWSZ];
};

static inline int git_oid_naive(const git_oid *a, const git_oid *b)
{
	return memcmp(a->id, b->id, GIT_OID_RAWSZ);
}

static inline int git_oid_cmp1(const git_oid *a, const git_oid *b)
{
	const unsigned char *sha1 = a->id;
	const unsigned char *sha2 = b->id;
	int i;

	for (i = 0; i < GIT_OID_RAWSZ; i++, sha1++, sha2++) {
		if (*sha1 != *sha2)
			return *sha1 - *sha2;
	}

	return 0;
}

static inline int git_oid_cmp2(const git_oid *a, const git_oid *b)
{
	const uint32_t *sha1 = (uint32_t *)a->id;
	const uint32_t *sha2 = (uint32_t *)b->id;
	int i;

#ifdef __GNUC__
	if (__builtin_expect(*sha1 != *sha2, 1))
#else
	if (*sha1 != *sha2)
#endif
		return *sha1 - *sha2;

	for (i = 1; i < GIT_OID_RAWSZ / sizeof(uint32_t); ++i) {
		if (sha1[i] != sha2[i])
			return sha1[i] - sha2[i];
	}

	return 0;
}

static inline int git_oid_cmp3(const git_oid *a, const git_oid *b)
{
	const uint32_t *sha1 = (uint32_t *)a->id;
	const uint32_t *sha2 = (uint32_t *)b->id;

	return	sha1[0] - sha2[0] ||
			sha1[1] - sha2[1] ||
			sha1[2] - sha2[2] ||
			sha1[3] - sha2[3] ||
			sha1[4] - sha2[4];
}

static inline int git_oid_cmp4(const git_oid *a, const git_oid *b)
{
	const uint32_t *sha1 = (uint32_t *)a->id;
	const uint32_t *sha2 = (uint32_t *)b->id;

	return	sha1[0] - sha2[0] |
			sha1[1] - sha2[1] |
			sha1[2] - sha2[2] |
			sha1[3] - sha2[3] |
			sha1[4] - sha2[4];
}

#define OID_CMP(a, b) git_oid_cmp2(a, b)
#define OID_COUNT (32000)

static git_oid *oid_array;

static void build_corpus()
{
	size_t i, j;

	srand(4225012);

	oid_array = malloc(OID_COUNT * sizeof(git_oid));

	for (i = 0; i < OID_COUNT; ++i) {
		git_oid *oid = &oid_array[i];

		for (j = 0; j < GIT_OID_RAWSZ; ++j)
			oid->id[j] = rand() & 0xff;
	}
}

static size_t test_run()
{
	size_t i, j, x = 0;

	for (i = 0; i < OID_COUNT; ++i) {
		git_oid *a = &oid_array[i];

		for (j = 0; j < OID_COUNT; ++j) {
			git_oid *b = &oid_array[j];
			x |= OID_CMP(a, b);
		}
	}

	return x;
}

int main(int argc, char *argv[])
{
	static int runs = 8;
	int i;
	double total = 0;
	size_t x = 0;

	build_corpus();

	for (i = 0; i < runs; ++i) {
		double start, end;

		start = get_time();
		x |= test_run();
		end = get_time();

		printf("Run %d: %fs\n", i + 1, end - start);
		total += end - start;
	}

	printf("AVG: %f\n", total / runs);
	return x;
}