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authorJeff King <peff@peff.net>2016-10-03 19:47:28 -0400
committerJunio C Hamano <gitster@pobox.com>2016-10-03 21:03:14 -0700
commit8e3f52d77854a19cb3fd2adee40be84c8a8bdacc (patch)
treed342eca5c1880a5286108a8e12e71eee8ca2b44a /sha1_name.c
parente6c587c733b4634030b353f4024794b08bc86892 (diff)
downloadgit-8e3f52d77854a19cb3fd2adee40be84c8a8bdacc.tar.gz
find_unique_abbrev: move logic out of get_short_sha1()jk/abbrev-auto
The get_short_sha1() is only about reading short sha1s; we do call it in a loop to check "is this long enough" for each object, but otherwise it should not need to know about things like our default_abbrev setting. So instead of asking it to set default_automatic_abbrev as a side-effect, let's just have find_unique_abbrev() pick the right place to start its loop. This requires a separate approximate_object_count() function, but that naturally belongs with the rest of sha1_file.c. Signed-off-by: Jeff King <peff@peff.net> Signed-off-by: Junio C Hamano <gitster@pobox.com>
Diffstat (limited to 'sha1_name.c')
-rw-r--r--sha1_name.c60
1 files changed, 35 insertions, 25 deletions
diff --git a/sha1_name.c b/sha1_name.c
index beb7ab588b..4a6f842692 100644
--- a/sha1_name.c
+++ b/sha1_name.c
@@ -15,7 +15,6 @@ typedef int (*disambiguate_hint_fn)(const unsigned char *, void *);
struct disambiguate_state {
int len; /* length of prefix in hex chars */
- unsigned int nrobjects;
char hex_pfx[GIT_SHA1_HEXSZ + 1];
unsigned char bin_pfx[GIT_SHA1_RAWSZ];
@@ -119,14 +118,6 @@ static void find_short_object_filename(struct disambiguate_state *ds)
if (strlen(de->d_name) != 38)
continue;
-
- /*
- * We only look at the one subdirectory, and we assume
- * each subdirectory is roughly similar, so each
- * object we find probably has 255 other objects in
- * the other fan-out directories.
- */
- ds->nrobjects += 256;
if (memcmp(de->d_name, ds->hex_pfx + 2, ds->len - 2))
continue;
memcpy(hex + 2, de->d_name, 38);
@@ -160,7 +151,6 @@ static void unique_in_pack(struct packed_git *p,
open_pack_index(p);
num = p->num_objects;
- ds->nrobjects += num;
last = num;
while (first < last) {
uint32_t mid = (first + last) / 2;
@@ -390,9 +380,6 @@ static int show_ambiguous_object(const unsigned char *sha1, void *data)
return 0;
}
-/* start from our historical default before the automatic abbreviation */
-static int default_automatic_abbrev = FALLBACK_DEFAULT_ABBREV;
-
static int get_short_sha1(const char *name, int len, unsigned char *sha1,
unsigned flags)
{
@@ -439,14 +426,6 @@ static int get_short_sha1(const char *name, int len, unsigned char *sha1,
for_each_abbrev(ds.hex_pfx, show_ambiguous_object, &ds);
}
- if (len < 16 && !status && (flags & GET_SHA1_AUTOMATIC)) {
- unsigned int expect_collision = 1 << (len * 2);
- if (ds.nrobjects > expect_collision) {
- default_automatic_abbrev = len+1;
- return SHORT_NAME_AMBIGUOUS;
- }
- }
-
return status;
}
@@ -476,22 +455,53 @@ int for_each_abbrev(const char *prefix, each_abbrev_fn fn, void *cb_data)
return ret;
}
+/*
+ * Return the slot of the most-significant bit set in "val". There are various
+ * ways to do this quickly with fls() or __builtin_clzl(), but speed is
+ * probably not a big deal here.
+ */
+static unsigned msb(unsigned long val)
+{
+ unsigned r = 0;
+ while (val >>= 1)
+ r++;
+ return r;
+}
+
int find_unique_abbrev_r(char *hex, const unsigned char *sha1, int len)
{
int status, exists;
- int flags = GET_SHA1_QUIETLY;
if (len < 0) {
- flags |= GET_SHA1_AUTOMATIC;
- len = default_automatic_abbrev;
+ unsigned long count = approximate_object_count();
+ /*
+ * Add one because the MSB only tells us the highest bit set,
+ * not including the value of all the _other_ bits (so "15"
+ * is only one off of 2^4, but the MSB is the 3rd bit.
+ */
+ len = msb(count) + 1;
+ /*
+ * We now know we have on the order of 2^len objects, which
+ * expects a collision at 2^(len/2). But we also care about hex
+ * chars, not bits, and there are 4 bits per hex. So all
+ * together we need to divide by 2; but we also want to round
+ * odd numbers up, hence adding one before dividing.
+ */
+ len = (len + 1) / 2;
+ /*
+ * For very small repos, we stick with our regular fallback.
+ */
+ if (len < FALLBACK_DEFAULT_ABBREV)
+ len = FALLBACK_DEFAULT_ABBREV;
}
+
sha1_to_hex_r(hex, sha1);
if (len == 40 || !len)
return 40;
exists = has_sha1_file(sha1);
while (len < 40) {
unsigned char sha1_ret[20];
- status = get_short_sha1(hex, len, sha1_ret, flags);
+ status = get_short_sha1(hex, len, sha1_ret, GET_SHA1_QUIETLY);
if (exists
? !status
: status == SHORT_NAME_NOT_FOUND) {