Re: [PATCH v4 3/4] sha1_name: parse less while finding common prefix

[Jeff King]

On Sun, Oct 08, 2017 at 02:49:41PM -0400, Derrick Stolee wrote:

> +static inline char get_hex_char_from_oid(const struct object_id *oid,
> +  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];
> +}

Should "pos" be unsigned? I don't think it matters much in practice (as
long as it's not negative, the results are well defined by the standard,
and this clearly will be between 0 and 40). But it seems funny that we
consistently use unsigned in the rest of the caller and then implicitly
convert to signed here.

-Peff

[PATCH v4 3/4] sha1_name: parse less while finding common prefix

[Derrick Stolee]

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 
---
 sha1_name.c | 14 --
 1 file changed, 12 insertions(+), 2 deletions(-)

diff --git a/sha1_name.c b/sha1_name.c
index f2a1ebe49..5081aeb71 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,
+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)
-- 
2.14.1.538.g56ec8fc98.dirty