builtin/log: use size_t to track indices

Similar as with the preceding commit, adapt "builtin/log.c" so that it
tracks array indices via `size_t` instead of using signed integers. This
fixes a couple of -Wsign-compare warnings and prepares the code for
a similar refactoring of `repo_get_merge_bases_many()` in a subsequent
commit.

Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Author: pks-t

builtin/log.c

@@ -1746,11 +1746,12 @@ struct base_tree_info {
 
 static struct commit *get_base_commit(const struct format_config *cfg,
 				      struct commit **list,
-				      int total)
+				      size_t total)
 {
 	struct commit *base = NULL;
 	struct commit **rev;
-	int i = 0, rev_nr = 0, auto_select, die_on_failure, ret;
+	int auto_select, die_on_failure, ret;
+	size_t i = 0, rev_nr = 0;
 
 	switch (cfg->auto_base) {
 	case AUTO_BASE_NEVER:
@@ -1885,13 +1886,12 @@ define_commit_slab(commit_base, int);
 static void prepare_bases(struct base_tree_info *bases,
 			  struct commit *base,
 			  struct commit **list,
-			  int total)
+			  size_t total)
 {
 	struct commit *commit;
 	struct rev_info revs;
 	struct diff_options diffopt;
 	struct commit_base commit_base;
-	int i;
 
 	if (!base)
 		return;
@@ -1906,7 +1906,7 @@ static void prepare_bases(struct base_tree_info *bases,
 	repo_init_revisions(the_repository, &revs, NULL);
 	revs.max_parents = 1;
 	revs.topo_order = 1;
-	for (i = 0; i < total; i++) {
+	for (size_t i = 0; i < total; i++) {
 		list[i]->object.flags &= ~UNINTERESTING;
 		add_pending_object(&revs, &list[i]->object, "rev_list");
 		*commit_base_at(&commit_base, list[i]) = 1;
@@ -2007,7 +2007,7 @@ int cmd_format_patch(int argc,
 	struct rev_info rev;
 	char *to_free = NULL;
 	struct setup_revision_opt s_r_opt;
-	int nr = 0, total, i;
+	size_t nr = 0, total, i;
 	int use_stdout = 0;
 	int start_number = -1;
 	int just_numbers = 0;
@@ -2500,11 +2500,14 @@ int cmd_format_patch(int argc,
 
 	if (show_progress)
 		progress = start_delayed_progress(_("Generating patches"), total);
-	while (0 <= --nr) {
+	for (i = 0; i < nr; i++) {
+		size_t idx = nr - i - 1;
 		int shown;
-		display_progress(progress, total - nr);
-		commit = list[nr];
-		rev.nr = total - nr + (start_number - 1);
+
+		display_progress(progress, total - idx);
+		commit = list[idx];
+		rev.nr = total - idx + (start_number - 1);
+
 		/* Make the second and subsequent mails replies to the first */
 		if (cfg.thread) {
 			/* Have we already had a message ID? */