introduce hex2chr() for converting two hexadecimal digits to a character

Add and use a helper function that decodes the char value of two
hexadecimal digits.  It returns a negative number on error, avoids
running over the end of the given string and doesn't shift negative
values.

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

1 files changed, 5 insertions, 8 deletions

diff --git a/pretty.c b/pretty.c
index b27165603..37e74cbb8 100644
--- a/pretty.c
+++ b/pretty.c
@@ -1063,7 +1063,7 @@ static size_t format_commit_one(struct strbuf *sb, /* in UTF-8 */
 	const struct commit *commit = c->commit;
 	const char *msg = c->message;
 	struct commit_list *p;
-	int h1, h2;
+	int ch;
 
 	/* these are independent of the commit */
 	switch (placeholder[0]) {
@@ -1087,14 +1087,11 @@ static size_t format_commit_one(struct strbuf *sb, /* in UTF-8 */
 		return 1;
 	case 'x':
 		/* %x00 == NUL, %x0a == LF, etc. */
-		if (0 <= (h1 = hexval_table[0xff & placeholder[1]]) &&
-		    h1 <= 16 &&
-		    0 <= (h2 = hexval_table[0xff & placeholder[2]]) &&
-		    h2 <= 16) {
-			strbuf_addch(sb, (h1<<4)|h2);
-			return 3;
-		} else
+		ch = hex2chr(placeholder + 1);
+		if (ch < 0)
 			return 0;
+		strbuf_addch(sb, ch);
+		return 3;
 	case 'w':
 		if (placeholder[1] == '(') {
 			unsigned long width = 0, indent1 = 0, indent2 = 0;