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Merge branch 'ds/name-hash-tweaks'

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"git pack-objects" and its wrapper "git repack" learned an option
to use an alternative path-hash function to improve delta-base
selection to produce a packfile with deeper history than window
size.

* ds/name-hash-tweaks:
  pack-objects: prevent name hash version change
  test-tool: add helper for name-hash values
  p5313: add size comparison test
  pack-objects: add GIT_TEST_NAME_HASH_VERSION
  repack: add --name-hash-version option
  pack-objects: add --name-hash-version option
  pack-objects: create new name-hash function version
This commit is contained in:
Junio C Hamano
2025-02-12 10:08:51 -08:00
parent 388218fac7 b4cf68476a
commit aae91a86fb
22 changed files with 389 additions and 16 deletions
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28
pack-objects.h
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@ -208,6 +208,34 @@ static inline uint32_t pack_name_hash(const char *name)
return hash;
}
static inline uint32_t pack_name_hash_v2(const unsigned char *name)
{
uint32_t hash = 0, base = 0, c;
if (!name)
return 0;
while ((c = *name++)) {
if (isspace(c))
continue;
if (c == '/') {
base = (base >> 6) ^ hash;
hash = 0;
} else {
/*
* 'c' is only a single byte. Reverse it and move
* it to the top of the hash, moving the rest to
* less-significant bits.
*/
c = (c & 0xF0) >> 4 | (c & 0x0F) << 4;
c = (c & 0xCC) >> 2 | (c & 0x33) << 2;
c = (c & 0xAA) >> 1 | (c & 0x55) << 1;
hash = (hash >> 2) + (c << 24);
}
}
return (base >> 6) ^ hash;
}
static inline enum object_type oe_type(const struct object_entry *e)
{
return e->type_valid ? e->type_ : OBJ_BAD;