freshlybakedca.ke
Git fork
1#define USE_THE_REPOSITORY_VARIABLE
2
3#include "git-compat-util.h"
4#include "hash.h"
5#include "hash-lookup.h"
6#include "read-cache-ll.h"
7
8static uint32_t take2(const struct object_id *oid, size_t ofs)
9{
10 return ((oid->hash[ofs] << 8) | oid->hash[ofs + 1]);
11}
12
13/*
14 * Conventional binary search loop looks like this:
15 *
16 * do {
17 * int mi = lo + (hi - lo) / 2;
18 * int cmp = "entry pointed at by mi" minus "target";
19 * if (!cmp)
20 * return (mi is the wanted one)
21 * if (cmp > 0)
22 * hi = mi; "mi is larger than target"
23 * else
24 * lo = mi+1; "mi is smaller than target"
25 * } while (lo < hi);
26 *
27 * The invariants are:
28 *
29 * - When entering the loop, lo points at a slot that is never
30 * above the target (it could be at the target), hi points at a
31 * slot that is guaranteed to be above the target (it can never
32 * be at the target).
33 *
34 * - We find a point 'mi' between lo and hi (mi could be the same
35 * as lo, but never can be the same as hi), and check if it hits
36 * the target. There are three cases:
37 *
38 * - if it is a hit, we are happy.
39 *
40 * - if it is strictly higher than the target, we update hi with
41 * it.
42 *
43 * - if it is strictly lower than the target, we update lo to be
44 * one slot after it, because we allow lo to be at the target.
45 *
46 * When choosing 'mi', we do not have to take the "middle" but
47 * anywhere in between lo and hi, as long as lo <= mi < hi is
48 * satisfied. When we somehow know that the distance between the
49 * target and lo is much shorter than the target and hi, we could
50 * pick mi that is much closer to lo than the midway.
51 */
52/*
53 * The table should contain "nr" elements.
54 * The oid of element i (between 0 and nr - 1) should be returned
55 * by "fn(i, table)".
56 */
57int oid_pos(const struct object_id *oid, const void *table, size_t nr,
58 oid_access_fn fn)
59{
60 size_t hi = nr;
61 size_t lo = 0;
62 size_t mi = 0;
63
64 if (!nr)
65 return -1;
66
67 if (nr != 1) {
68 size_t lov, hiv, miv, ofs;
69
70 for (ofs = 0; ofs < the_hash_algo->rawsz - 2; ofs += 2) {
71 lov = take2(fn(0, table), ofs);
72 hiv = take2(fn(nr - 1, table), ofs);
73 miv = take2(oid, ofs);
74 if (miv < lov)
75 return -1;
76 if (hiv < miv)
77 return index_pos_to_insert_pos(nr);
78 if (lov != hiv) {
79 /*
80 * At this point miv could be equal
81 * to hiv (but hash could still be higher);
82 * the invariant of (mi < hi) should be
83 * kept.
84 */
85 mi = (nr - 1) * (miv - lov) / (hiv - lov);
86 if (lo <= mi && mi < hi)
87 break;
88 BUG("assertion failed in binary search");
89 }
90 }
91 }
92
93 do {
94 int cmp;
95 cmp = oidcmp(fn(mi, table), oid);
96 if (!cmp)
97 return mi;
98 if (cmp > 0)
99 hi = mi;
100 else
101 lo = mi + 1;
102 mi = lo + (hi - lo) / 2;
103 } while (lo < hi);
104 return index_pos_to_insert_pos(lo);
105}
106
107int bsearch_hash(const unsigned char *hash, const uint32_t *fanout_nbo,
108 const unsigned char *table, size_t stride, uint32_t *result)
109{
110 uint32_t hi, lo;
111
112 hi = ntohl(fanout_nbo[*hash]);
113 lo = ((*hash == 0x0) ? 0 : ntohl(fanout_nbo[*hash - 1]));
114
115 while (lo < hi) {
116 unsigned mi = lo + (hi - lo) / 2;
117 int cmp = hashcmp(table + mi * stride, hash,
118 the_repository->hash_algo);
119
120 if (!cmp) {
121 if (result)
122 *result = mi;
123 return 1;
124 }
125 if (cmp > 0)
126 hi = mi;
127 else
128 lo = mi + 1;
129 }
130
131 if (result)
132 *result = lo;
133 return 0;
134}