[PATCH v6 08/12] t/helper: add a test helper to compute hash speed

["brian m. carlson" <sandals@xxxxxxxxxxxxxxxxxxxx>]

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@xxxxxxxxxxxxxxxxxxxx>
---
 Makefile                   |  1 +
 t/helper/test-hash-speed.c | 61 ++++++++++++++++++++++++++++++++++++++
 t/helper/test-tool.c       |  1 +
 t/helper/test-tool.h       |  1 +
 4 files changed, 64 insertions(+)
 create mode 100644 t/helper/test-hash-speed.c

diff --git a/Makefile b/Makefile
index daf0b198ec..c6f06bf50b 100644
--- a/Makefile
+++ b/Makefile
@@ -726,6 +726,7 @@ TEST_BUILTINS_OBJS += test-example-decorate.o
 TEST_BUILTINS_OBJS += test-genrandom.o
 TEST_BUILTINS_OBJS += test-hash.o
 TEST_BUILTINS_OBJS += test-hashmap.o
+TEST_BUILTINS_OBJS += test-hash-speed.o
 TEST_BUILTINS_OBJS += test-index-version.o
 TEST_BUILTINS_OBJS += test-json-writer.o
 TEST_BUILTINS_OBJS += test-lazy-init-name-hash.o
diff --git a/t/helper/test-hash-speed.c b/t/helper/test-hash-speed.c
new file mode 100644
index 0000000000..432233c7f0
--- /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);
+}
diff --git a/t/helper/test-tool.c b/t/helper/test-tool.c
index bfb195b1a8..c222d532a2 100644
--- a/t/helper/test-tool.c
+++ b/t/helper/test-tool.c
@@ -20,6 +20,7 @@ static struct test_cmd cmds[] = {
 	{ "example-decorate", cmd__example_decorate },
 	{ "genrandom", cmd__genrandom },
 	{ "hashmap", cmd__hashmap },
+	{ "hash-speed", cmd__hash_speed },
 	{ "index-version", cmd__index_version },
 	{ "json-writer", cmd__json_writer },
 	{ "lazy-init-name-hash", cmd__lazy_init_name_hash },
diff --git a/t/helper/test-tool.h b/t/helper/test-tool.h
index b5b7712a1d..70dafb7649 100644
--- a/t/helper/test-tool.h
+++ b/t/helper/test-tool.h
@@ -16,6 +16,7 @@ int cmd__dump_untracked_cache(int argc, const char **argv);
 int cmd__example_decorate(int argc, const char **argv);
 int cmd__genrandom(int argc, const char **argv);
 int cmd__hashmap(int argc, const char **argv);
+int cmd__hash_speed(int argc, const char **argv);
 int cmd__index_version(int argc, const char **argv);
 int cmd__json_writer(int argc, const char **argv);
 int cmd__lazy_init_name_hash(int argc, const char **argv);