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 4b6c08975d086a11cb93194345810955489008c8..733815f1dc0ee8594d62968f51bf463b4ab2d8c4 100644 (file)
--- 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)