log-tree: use decimal_width()

Reduce code duplication by calling decimal_width() to count the digits
in the number of commits instead of calculating it locally.

It also has the advantage of returning int, which is the exact type
expected by the printf()-like function strbuf_addf() for field width
arguments.

Additionally, decimal_width() supports numbers bigger than 1410065407,
which is (hopefully) just a theoretical advantage.

Signed-off-by: René Scharfe <l.s.r@web.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Author: rscharfe

log-tree.c

@@ -29,6 +29,7 @@
 #include "tree.h"
 #include "wildmatch.h"
 #include "write-or-die.h"
+#include "pager.h"
 
 static struct decoration name_decoration = { "object names" };
 static int decoration_loaded;
@@ -406,16 +407,6 @@ void show_decorations(struct rev_info *opt, struct commit *commit)
 	strbuf_release(&sb);
 }
 
-static unsigned int digits_in_number(unsigned int number)
-{
-	unsigned int i = 10, result = 1;
-	while (i <= number) {
-		i *= 10;
-		result++;
-	}
-	return result;
-}
-
 void fmt_output_subject(struct strbuf *filename,
 			const char *subject,
 			struct rev_info *info)
@@ -459,7 +450,7 @@ void fmt_output_email_subject(struct strbuf *sb, struct rev_info *opt)
 		strbuf_addf(sb, "Subject: [%s%s%0*d/%d] ",
 			    opt->subject_prefix,
 			    *opt->subject_prefix ? " " : "",
-			    digits_in_number(opt->total),
+			    decimal_width(opt->total),
 			    opt->nr, opt->total);
 	} else if (opt->total == 0 && opt->subject_prefix && *opt->subject_prefix) {
 		strbuf_addf(sb, "Subject: [%s] ",