Commit b4e00f73 authored by Jonathan Tan's avatar Jonathan Tan Committed by Junio C Hamano

packfile: refactor hash search with fanout table

Subsequent patches will introduce file formats that make use of a fanout
array and a sorted table containing hashes, just like packfiles.
Refactor the hash search in packfile.c into its own function, so that
those patches can make use of it as well.
Signed-off-by: default avatarJonathan Tan <jonathantanmy@google.com>
Signed-off-by: default avatarJunio C Hamano <gitster@pobox.com>
parent 4669e7d6
......@@ -1712,7 +1712,8 @@ off_t find_pack_entry_one(const unsigned char *sha1,
{
const uint32_t *level1_ofs = p->index_data;
const unsigned char *index = p->index_data;
unsigned hi, lo, stride;
unsigned stride;
uint32_t result;
if (!index) {
if (open_pack_index(p))
......@@ -1725,8 +1726,6 @@ off_t find_pack_entry_one(const unsigned char *sha1,
index += 8;
}
index += 4 * 256;
hi = ntohl(level1_ofs[*sha1]);
lo = ((*sha1 == 0x0) ? 0 : ntohl(level1_ofs[*sha1 - 1]));
if (p->index_version > 1) {
stride = 20;
} else {
......@@ -1734,17 +1733,8 @@ off_t find_pack_entry_one(const unsigned char *sha1,
index += 4;
}
while (lo < hi) {
unsigned mi = lo + (hi - lo) / 2;
int cmp = hashcmp(index + mi * stride, sha1);
if (!cmp)
return nth_packed_object_offset(p, mi);
if (cmp > 0)
hi = mi;
else
lo = mi+1;
}
if (bsearch_hash(sha1, level1_ofs, index, stride, &result))
return nth_packed_object_offset(p, result);
return 0;
}
......
......@@ -99,3 +99,31 @@ int sha1_pos(const unsigned char *sha1, void *table, size_t nr,
} while (lo < hi);
return -lo-1;
}
int bsearch_hash(const unsigned char *sha1, const uint32_t *fanout_nbo,
const unsigned char *table, size_t stride, uint32_t *result)
{
uint32_t hi, lo;
hi = ntohl(fanout_nbo[*sha1]);
lo = ((*sha1 == 0x0) ? 0 : ntohl(fanout_nbo[*sha1 - 1]));
while (lo < hi) {
unsigned mi = lo + (hi - lo) / 2;
int cmp = hashcmp(table + mi * stride, sha1);
if (!cmp) {
if (result)
*result = mi;
return 1;
}
if (cmp > 0)
hi = mi;
else
lo = mi + 1;
}
if (result)
*result = lo;
return 0;
}
......@@ -7,4 +7,26 @@ extern int sha1_pos(const unsigned char *sha1,
void *table,
size_t nr,
sha1_access_fn fn);
/*
* Searches for sha1 in table, using the given fanout table to determine the
* interval to search, then using binary search. Returns 1 if found, 0 if not.
*
* Takes the following parameters:
*
* - sha1: the hash to search for
* - fanout_nbo: a 256-element array of NETWORK-order 32-bit integers; the
* integer at position i represents the number of elements in table whose
* first byte is less than or equal to i
* - table: a sorted list of hashes with optional extra information in between
* - stride: distance between two consecutive elements in table (should be
* GIT_MAX_RAWSZ or greater)
* - result: if not NULL, this function stores the element index of the
* position found (if the search is successful) or the index of the least
* element that is greater than sha1 (if the search is not successful)
*
* This function does not verify the validity of the fanout table.
*/
int bsearch_hash(const unsigned char *sha1, const uint32_t *fanout_nbo,
const unsigned char *table, size_t stride, uint32_t *result);
#endif
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