test-mergesort: add generate subcommand

Add a subcommand for printing test data.  It can be used to generate
special test cases and feed them into the sort subcommand or sort(1) for
performance measurements.  It may also be useful to illustrate the
effect of distributions, modes and their parameters.

It generates n integers with the specified distribution and its
distribution-specific parameter m.  E.g. m is the maximum value for
the plateau distribution and the length and height of individual teeth
of the sawtooth distribution.

The generated values are printed as zero-padded eight-digit hexadecimal
numbers to make sure alphabetic and numeric order are the same.

Signed-off-by: René Scharfe <[email protected]>
Signed-off-by: Junio C Hamano <[email protected]>

Author: rscharfe

t/helper/test-mergesort.c

@@ -98,6 +98,16 @@ static struct dist {
 	DIST(shuffle),
 };
 
+static const struct dist *get_dist_by_name(const char *name)
+{
+	int i;
+	for (i = 0; i < ARRAY_SIZE(dist); i++) {
+	       if (!strcmp(dist[i].name, name))
+		       return &dist[i];
+	}
+	return NULL;
+}
+
 static void mode_copy(int *arr, int n)
 {
 	/* nothing */
@@ -154,6 +164,41 @@ static struct mode {
 	MODE(dither),
 };
 
+static const struct mode *get_mode_by_name(const char *name)
+{
+	int i;
+	for (i = 0; i < ARRAY_SIZE(mode); i++) {
+	       if (!strcmp(mode[i].name, name))
+		       return &mode[i];
+	}
+	return NULL;
+}
+
+static int generate(int argc, const char **argv)
+{
+	const struct dist *dist = NULL;
+	const struct mode *mode = NULL;
+	int i, n, m, *arr;
+
+	if (argc != 4)
+		return 1;
+
+	dist = get_dist_by_name(argv[0]);
+	mode = get_mode_by_name(argv[1]);
+	n = strtol(argv[2], NULL, 10);
+	m = strtol(argv[3], NULL, 10);
+	if (!dist || !mode)
+		return 1;
+
+	ALLOC_ARRAY(arr, n);
+	dist->fn(arr, n, m);
+	mode->fn(arr, n);
+	for (i = 0; i < n; i++)
+		printf("%08x\n", arr[i]);
+	free(arr);
+	return 0;
+}
+
 static struct stats {
 	int get_next, set_next, compare;
 } stats;
@@ -278,11 +323,24 @@ static int run_tests(int argc, const char **argv)
 
 int cmd__mergesort(int argc, const char **argv)
 {
+	int i;
+	const char *sep;
+
+	if (argc == 6 && !strcmp(argv[1], "generate"))
+		return generate(argc - 2, argv + 2);
 	if (argc == 2 && !strcmp(argv[1], "sort"))
 		return sort_stdin();
 	if (argc > 1 && !strcmp(argv[1], "test"))
 		return run_tests(argc - 2, argv + 2);
-	fprintf(stderr, "usage: test-tool mergesort sort\n");
+	fprintf(stderr, "usage: test-tool mergesort generate <distribution> <mode> <n> <m>\n");
+	fprintf(stderr, "   or: test-tool mergesort sort\n");
 	fprintf(stderr, "   or: test-tool mergesort test [<n>...]\n");
+	fprintf(stderr, "\n");
+	for (i = 0, sep = "distributions: "; i < ARRAY_SIZE(dist); i++, sep = ", ")
+		fprintf(stderr, "%s%s", sep, dist[i].name);
+	fprintf(stderr, "\n");
+	for (i = 0, sep = "modes: "; i < ARRAY_SIZE(mode); i++, sep = ", ")
+		fprintf(stderr, "%s%s", sep, mode[i].name);
+	fprintf(stderr, "\n");
 	return 129;
 }