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3449f8c4 NP |
1 | #include "cache.h" |
2 | #include "pack-revindex.h" | |
3 | ||
4 | /* | |
5 | * Pack index for existing packs give us easy access to the offsets into | |
6 | * corresponding pack file where each object's data starts, but the entries | |
7 | * do not store the size of the compressed representation (uncompressed | |
8 | * size is easily available by examining the pack entry header). It is | |
9 | * also rather expensive to find the sha1 for an object given its offset. | |
10 | * | |
11 | * We build a hashtable of existing packs (pack_revindex), and keep reverse | |
12 | * index here -- pack index file is sorted by object name mapping to offset; | |
13 | * this pack_revindex[].revindex array is a list of offset/index_nr pairs | |
14 | * ordered by offset, so if you know the offset of an object, next offset | |
15 | * is where its packed representation ends and the index_nr can be used to | |
16 | * get the object sha1 from the main index. | |
17 | */ | |
18 | ||
19 | struct pack_revindex { | |
20 | struct packed_git *p; | |
21 | struct revindex_entry *revindex; | |
22 | }; | |
23 | ||
24 | static struct pack_revindex *pack_revindex; | |
25 | static int pack_revindex_hashsz; | |
26 | ||
27 | static int pack_revindex_ix(struct packed_git *p) | |
28 | { | |
29 | unsigned long ui = (unsigned long)p; | |
30 | int i; | |
31 | ||
32 | ui = ui ^ (ui >> 16); /* defeat structure alignment */ | |
33 | i = (int)(ui % pack_revindex_hashsz); | |
34 | while (pack_revindex[i].p) { | |
35 | if (pack_revindex[i].p == p) | |
36 | return i; | |
37 | if (++i == pack_revindex_hashsz) | |
38 | i = 0; | |
39 | } | |
40 | return -1 - i; | |
41 | } | |
42 | ||
1f5c74f6 | 43 | static void init_pack_revindex(void) |
3449f8c4 NP |
44 | { |
45 | int num; | |
46 | struct packed_git *p; | |
47 | ||
48 | for (num = 0, p = packed_git; p; p = p->next) | |
49 | num++; | |
50 | if (!num) | |
51 | return; | |
52 | pack_revindex_hashsz = num * 11; | |
53 | pack_revindex = xcalloc(sizeof(*pack_revindex), pack_revindex_hashsz); | |
54 | for (p = packed_git; p; p = p->next) { | |
55 | num = pack_revindex_ix(p); | |
56 | num = - 1 - num; | |
57 | pack_revindex[num].p = p; | |
58 | } | |
59 | /* revindex elements are lazily initialized */ | |
60 | } | |
61 | ||
62 | static int cmp_offset(const void *a_, const void *b_) | |
63 | { | |
64 | const struct revindex_entry *a = a_; | |
65 | const struct revindex_entry *b = b_; | |
66 | return (a->offset < b->offset) ? -1 : (a->offset > b->offset) ? 1 : 0; | |
67 | } | |
68 | ||
69 | /* | |
70 | * Ordered list of offsets of objects in the pack. | |
71 | */ | |
72 | static void create_pack_revindex(struct pack_revindex *rix) | |
73 | { | |
74 | struct packed_git *p = rix->p; | |
75 | int num_ent = p->num_objects; | |
76 | int i; | |
77 | const char *index = p->index_data; | |
78 | ||
79 | rix->revindex = xmalloc(sizeof(*rix->revindex) * (num_ent + 1)); | |
80 | index += 4 * 256; | |
81 | ||
82 | if (p->index_version > 1) { | |
83 | const uint32_t *off_32 = | |
84 | (uint32_t *)(index + 8 + p->num_objects * (20 + 4)); | |
85 | const uint32_t *off_64 = off_32 + p->num_objects; | |
86 | for (i = 0; i < num_ent; i++) { | |
87 | uint32_t off = ntohl(*off_32++); | |
88 | if (!(off & 0x80000000)) { | |
89 | rix->revindex[i].offset = off; | |
90 | } else { | |
91 | rix->revindex[i].offset = | |
92 | ((uint64_t)ntohl(*off_64++)) << 32; | |
93 | rix->revindex[i].offset |= | |
94 | ntohl(*off_64++); | |
95 | } | |
96 | rix->revindex[i].nr = i; | |
97 | } | |
98 | } else { | |
99 | for (i = 0; i < num_ent; i++) { | |
100 | uint32_t hl = *((uint32_t *)(index + 24 * i)); | |
101 | rix->revindex[i].offset = ntohl(hl); | |
102 | rix->revindex[i].nr = i; | |
103 | } | |
104 | } | |
105 | ||
106 | /* This knows the pack format -- the 20-byte trailer | |
107 | * follows immediately after the last object data. | |
108 | */ | |
109 | rix->revindex[num_ent].offset = p->pack_size - 20; | |
110 | rix->revindex[num_ent].nr = -1; | |
111 | qsort(rix->revindex, num_ent, sizeof(*rix->revindex), cmp_offset); | |
112 | } | |
113 | ||
114 | struct revindex_entry *find_pack_revindex(struct packed_git *p, off_t ofs) | |
115 | { | |
116 | int num; | |
117 | int lo, hi; | |
118 | struct pack_revindex *rix; | |
119 | struct revindex_entry *revindex; | |
120 | ||
1f5c74f6 NP |
121 | if (!pack_revindex_hashsz) |
122 | init_pack_revindex(); | |
3449f8c4 NP |
123 | num = pack_revindex_ix(p); |
124 | if (num < 0) | |
1f5c74f6 | 125 | die("internal error: pack revindex fubar"); |
3449f8c4 NP |
126 | |
127 | rix = &pack_revindex[num]; | |
128 | if (!rix->revindex) | |
129 | create_pack_revindex(rix); | |
130 | revindex = rix->revindex; | |
131 | ||
132 | lo = 0; | |
133 | hi = p->num_objects + 1; | |
134 | do { | |
135 | int mi = (lo + hi) / 2; | |
136 | if (revindex[mi].offset == ofs) { | |
137 | return revindex + mi; | |
138 | } else if (ofs < revindex[mi].offset) | |
139 | hi = mi; | |
140 | else | |
141 | lo = mi + 1; | |
142 | } while (lo < hi); | |
143 | die("internal error: pack revindex corrupt"); | |
144 | } | |
4b480c67 NP |
145 | |
146 | void discard_revindex(void) | |
147 | { | |
148 | if (pack_revindex_hashsz) { | |
149 | int i; | |
150 | for (i = 0; i < pack_revindex_hashsz; i++) | |
151 | if (pack_revindex[i].revindex) | |
152 | free(pack_revindex[i].revindex); | |
153 | free(pack_revindex); | |
154 | pack_revindex_hashsz = 0; | |
155 | } | |
156 | } |