Merge branch 'ds/name-hash-tweaks'

"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

1 files changed, 28 insertions, 0 deletions

diff --git a/pack-objects.h b/pack-objects.h
index 3f6f504203..d73e3843c9 100644
--- a/pack-objects.h
+++ b/pack-objects.h
@@ -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;