summaryrefslogtreecommitdiff
path: root/pack-revindex.c
blob: a8aa2cd6caefe7d37febdf5c3426cec043492b19 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
#include "cache.h"
#include "pack-revindex.h"

/*
 * Pack index for existing packs give us easy access to the offsets into
 * corresponding pack file where each object's data starts, but the entries
 * do not store the size of the compressed representation (uncompressed
 * size is easily available by examining the pack entry header).  It is
 * also rather expensive to find the sha1 for an object given its offset.
 *
 * We build a hashtable of existing packs (pack_revindex), and keep reverse
 * index here -- pack index file is sorted by object name mapping to offset;
 * this pack_revindex[].revindex array is a list of offset/index_nr pairs
 * ordered by offset, so if you know the offset of an object, next offset
 * is where its packed representation ends and the index_nr can be used to
 * get the object sha1 from the main index.
 */

struct pack_revindex {
	struct packed_git *p;
	struct revindex_entry *revindex;
};

static struct pack_revindex *pack_revindex;
static int pack_revindex_hashsz;

static int pack_revindex_ix(struct packed_git *p)
{
	unsigned long ui = (unsigned long)p;
	int i;

	ui = ui ^ (ui >> 16); /* defeat structure alignment */
	i = (int)(ui % pack_revindex_hashsz);
	while (pack_revindex[i].p) {
		if (pack_revindex[i].p == p)
			return i;
		if (++i == pack_revindex_hashsz)
			i = 0;
	}
	return -1 - i;
}

void init_pack_revindex(void)
{
	int num;
	struct packed_git *p;

	for (num = 0, p = packed_git; p; p = p->next)
		num++;
	if (!num)
		return;
	pack_revindex_hashsz = num * 11;
	pack_revindex = xcalloc(sizeof(*pack_revindex), pack_revindex_hashsz);
	for (p = packed_git; p; p = p->next) {
		num = pack_revindex_ix(p);
		num = - 1 - num;
		pack_revindex[num].p = p;
	}
	/* revindex elements are lazily initialized */
}

static int cmp_offset(const void *a_, const void *b_)
{
	const struct revindex_entry *a = a_;
	const struct revindex_entry *b = b_;
	return (a->offset < b->offset) ? -1 : (a->offset > b->offset) ? 1 : 0;
}

/*
 * Ordered list of offsets of objects in the pack.
 */
static void create_pack_revindex(struct pack_revindex *rix)
{
	struct packed_git *p = rix->p;
	int num_ent = p->num_objects;
	int i;
	const char *index = p->index_data;

	rix->revindex = xmalloc(sizeof(*rix->revindex) * (num_ent + 1));
	index += 4 * 256;

	if (p->index_version > 1) {
		const uint32_t *off_32 =
			(uint32_t *)(index + 8 + p->num_objects * (20 + 4));
		const uint32_t *off_64 = off_32 + p->num_objects;
		for (i = 0; i < num_ent; i++) {
			uint32_t off = ntohl(*off_32++);
			if (!(off & 0x80000000)) {
				rix->revindex[i].offset = off;
			} else {
				rix->revindex[i].offset =
					((uint64_t)ntohl(*off_64++)) << 32;
				rix->revindex[i].offset |=
					ntohl(*off_64++);
			}
			rix->revindex[i].nr = i;
		}
	} else {
		for (i = 0; i < num_ent; i++) {
			uint32_t hl = *((uint32_t *)(index + 24 * i));
			rix->revindex[i].offset = ntohl(hl);
			rix->revindex[i].nr = i;
		}
	}

	/* This knows the pack format -- the 20-byte trailer
	 * follows immediately after the last object data.
	 */
	rix->revindex[num_ent].offset = p->pack_size - 20;
	rix->revindex[num_ent].nr = -1;
	qsort(rix->revindex, num_ent, sizeof(*rix->revindex), cmp_offset);
}

struct revindex_entry *find_pack_revindex(struct packed_git *p, off_t ofs)
{
	int num;
	int lo, hi;
	struct pack_revindex *rix;
	struct revindex_entry *revindex;

	num = pack_revindex_ix(p);
	if (num < 0)
		die("internal error: pack revindex uninitialized");

	rix = &pack_revindex[num];
	if (!rix->revindex)
		create_pack_revindex(rix);
	revindex = rix->revindex;

	lo = 0;
	hi = p->num_objects + 1;
	do {
		int mi = (lo + hi) / 2;
		if (revindex[mi].offset == ofs) {
			return revindex + mi;
		} else if (ofs < revindex[mi].offset)
			hi = mi;
		else
			lo = mi + 1;
	} while (lo < hi);
	die("internal error: pack revindex corrupt");
}