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, 2 insertions, 21 deletions

diff --git a/pkt-line.c b/pkt-line.c
index 62fdb37..30489c6 100644
--- a/pkt-line.c
+++ b/pkt-line.c
@@ -172,27 +172,8 @@ static int get_packet_data(int fd, char **src_buf, size_t *src_size,
 
 static int packet_length(const char *linelen)
 {
-	int n;
-	int len = 0;
-
-	for (n = 0; n < 4; n++) {
-		unsigned char c = linelen[n];
-		len <<= 4;
-		if (c >= '0' && c <= '9') {
-			len += c - '0';
-			continue;
-		}
-		if (c >= 'a' && c <= 'f') {
-			len += c - 'a' + 10;
-			continue;
-		}
-		if (c >= 'A' && c <= 'F') {
-			len += c - 'A' + 10;
-			continue;
-		}
-		return -1;
-	}
-	return len;
+	int val = hex2chr(linelen);
+	return (val < 0) ? val : (val << 8) | hex2chr(linelen + 2);
 }
 
 int packet_read(int fd, char **src_buf, size_t *src_len,