git-rev-parse: support show sha1 names for pack entries

This is actually subtly wrong.  If a short match is found in the object
directory, but would _also_ match another SHA1 ID in a pack (or it shows
in one pack but not another), we'll never have done the pack lookup, and
we think it's unique.

I can't find it in myself to care.  You really want to use enough of a
SHA1 that there is never any ambiguity.

diff --git a/rev-parse.c b/rev-parse.c
index 95da465..d62efda 100644 (file)
--- a/rev-parse.c
+++ b/rev-parse.c
@@ -131,8 +131,57 @@ static int find_short_object_filename(int len, const char *name, unsigned char *
        return 0;
 }
 
+static int match_sha(unsigned len, const unsigned char *a, const unsigned char *b)
+{
+       do {
+               if (*a != *b)
+                       return 0;
+               a++;
+               b++;
+               len -= 2;
+       } while (len > 1);
+       if (len)
+               if ((*a ^ *b) & 0xf0)
+                       return 0;
+       return 1;
+}
+
 static int find_short_packed_object(int len, const unsigned char *match, unsigned char *sha1)
 {
+       struct packed_git *p;
+
+       prepare_packed_git();
+       for (p = packed_git; p; p = p->next) {
+               unsigned num = num_packed_objects(p);
+               unsigned first = 0, last = num;
+               while (first < last) {
+                       unsigned mid = (first + last) / 2;
+                       unsigned char now[20];
+                       int cmp;
+
+                       nth_packed_object_sha1(p, mid, now);
+                       cmp = memcmp(match, now, 20);
+                       if (!cmp) {
+                               first = mid;
+                               break;
+                       }
+                       if (cmp > 0) {
+                               first = mid+1;
+                               continue;
+                       }
+                       last = mid;
+               }
+               if (first < num) {
+                       unsigned char now[20], next[20];
+                       nth_packed_object_sha1(p, first, now);
+                       if (match_sha(len, match, now)) {
+                               if (nth_packed_object_sha1(p, first+1, next) || !match_sha(len, match, next)) {
+                                       memcpy(sha1, now, 20);
+                                       return 1;
+                               }
+                       }
+               }       
+       }
        return 0;
 }