From: Derrick Stolee <dstolee@microsoft.com>
Date: Thu, 12 Oct 2017 12:02:19 +0000 (-0400)
Subject: sha1_name: parse less while finding common prefix
X-Git-Tag: v2.16.0-rc0~165^2~1
X-Git-Url: http://git.ipfire.org/?a=commitdiff_plain;h=a42d6fd274940be9c0fa6ada738e7611d011a1fc;p=thirdparty%2Fgit.git

sha1_name: parse less while finding common prefix

Create get_hex_char_from_oid() to parse oids one hex character at a
time. This prevents unnecessary copying of hex characters in
extend_abbrev_len() when finding the length of a common prefix.

Signed-off-by: Derrick Stolee <dstolee@microsoft.com>
Reviewed-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
---

diff --git a/sha1_name.c b/sha1_name.c
index 4b6c08975d..733815f1dc 100644
--- a/sha1_name.c
+++ b/sha1_name.c
@@ -480,13 +480,23 @@ struct min_abbrev_data {
 	char *hex;
 };
 
+static inline char get_hex_char_from_oid(const struct object_id *oid,
+					 unsigned int pos)
+{
+	static const char hex[] = "0123456789abcdef";
+
+	if ((pos & 1) == 0)
+		return hex[oid->hash[pos >> 1] >> 4];
+	else
+		return hex[oid->hash[pos >> 1] & 0xf];
+}
+
 static int extend_abbrev_len(const struct object_id *oid, void *cb_data)
 {
 	struct min_abbrev_data *mad = cb_data;
 
-	char *hex = oid_to_hex(oid);
 	unsigned int i = mad->init_len;
-	while (mad->hex[i] && mad->hex[i] == hex[i])
+	while (mad->hex[i] && mad->hex[i] == get_hex_char_from_oid(oid, i))
 		i++;
 
 	if (i < GIT_MAX_RAWSZ && i >= mad->cur_len)