t/helper: add a test helper to compute hash speed

Add a utility (which is less for the testsuite and more for developers)
that can compute hash speeds for whatever hash algorithms are
implemented.  This allows developers to test their personal systems to
determine the performance characteristics of various algorithms.

Signed-off-by: brian m. carlson <sandals@crustytoothpaste.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 61 insertions, 0 deletions

diff --git a/t/helper/test-hash-speed.c b/t/helper/test-hash-speed.c
new file mode 100644
index 0000000..432233c
--- /dev/null
+++ b/t/helper/test-hash-speed.c
@@ -0,0 +1,61 @@
+#include "test-tool.h"
+#include "cache.h"
+
+#define NUM_SECONDS 3
+
+static inline void compute_hash(const struct git_hash_algo *algo, git_hash_ctx *ctx, uint8_t *final, const void *p, size_t len)
+{
+	algo->init_fn(ctx);
+	algo->update_fn(ctx, p, len);
+	algo->final_fn(final, ctx);
+}
+
+int cmd__hash_speed(int ac, const char **av)
+{
+	git_hash_ctx ctx;
+	unsigned char hash[GIT_MAX_RAWSZ];
+	clock_t initial, start, end;
+	unsigned bufsizes[] = { 64, 256, 1024, 8192, 16384 };
+	int i;
+	void *p;
+	const struct git_hash_algo *algo = NULL;
+
+	if (ac == 2) {
+		for (i = 1; i < GIT_HASH_NALGOS; i++) {
+			if (!strcmp(av[1], hash_algos[i].name)) {
+				algo = &hash_algos[i];
+				break;
+			}
+		}
+	}
+	if (!algo)
+		die("usage: test-tool hash-speed algo_name");
+
+	/* Use this as an offset to make overflow less likely. */
+	initial = clock();
+
+	printf("algo: %s\n", algo->name);
+
+	for (i = 0; i < ARRAY_SIZE(bufsizes); i++) {
+		unsigned long j, kb;
+		double kb_per_sec;
+		p = xcalloc(1, bufsizes[i]);
+		start = end = clock() - initial;
+		for (j = 0; ((end - start) / CLOCKS_PER_SEC) < NUM_SECONDS; j++) {
+			compute_hash(algo, &ctx, hash, p, bufsizes[i]);
+
+			/*
+			 * Only check elapsed time every 128 iterations to avoid
+			 * dominating the runtime with system calls.
+			 */
+			if (!(j & 127))
+				end = clock() - initial;
+		}
+		kb = j * bufsizes[i];
+		kb_per_sec = kb / (1024 * ((double)end - start) / CLOCKS_PER_SEC);
+		printf("size %u: %lu iters; %lu KiB; %0.2f KiB/s\n", bufsizes[i], j, kb, kb_per_sec);
+		free(p);
+	}
+
+	exit(0);
+}