test-delta needs zlib to compile
[git/git.git] / diff-delta.c
CommitLineData
a310d434
NP
1/*
2 * diff-delta.c: generate a delta between two buffers
3 *
4 * Many parts of this file have been lifted from LibXDiff version 0.10.
5 * http://www.xmailserver.org/xdiff-lib.html
6 *
7 * LibXDiff was written by Davide Libenzi <davidel@xmailserver.org>
8 * Copyright (C) 2003 Davide Libenzi
9 *
10 * Many mods for GIT usage by Nicolas Pitre <nico@cam.org>, (C) 2005.
11 *
12 * This file is free software; you can redistribute it and/or
13 * modify it under the terms of the GNU Lesser General Public
14 * License as published by the Free Software Foundation; either
15 * version 2.1 of the License, or (at your option) any later version.
16 *
17 * Use of this within git automatically means that the LGPL
18 * licensing gets turned into GPLv2 within this project.
19 */
20
21#include <stdlib.h>
8e1454b5
NP
22#include <string.h>
23#include <zlib.h>
a310d434
NP
24#include "delta.h"
25
26
27/* block size: min = 16, max = 64k, power of 2 */
28#define BLK_SIZE 16
29
30#define MIN(a, b) ((a) < (b) ? (a) : (b))
31
32#define GR_PRIME 0x9e370001
8e1454b5 33#define HASH(v, shift) (((unsigned int)(v) * GR_PRIME) >> (shift))
a310d434 34
8e1454b5 35struct index {
a310d434 36 const unsigned char *ptr;
8e1454b5
NP
37 unsigned int val;
38 struct index *next;
39};
a310d434 40
8e1454b5
NP
41static struct index ** delta_index(const unsigned char *buf,
42 unsigned long bufsize,
43 unsigned int *hash_shift)
a310d434 44{
8e1454b5
NP
45 unsigned int hsize, hshift, entries, blksize, i;
46 const unsigned char *data;
47 struct index *entry, **hash;
48 void *mem;
49
50 /* determine index hash size */
51 entries = (bufsize + BLK_SIZE - 1) / BLK_SIZE;
52 hsize = entries / 4;
53 for (i = 4; (1 << i) < hsize && i < 16; i++);
54 hsize = 1 << i;
55 hshift = 32 - i;
56 *hash_shift = hshift;
57
58 /* allocate lookup index */
59 mem = malloc(hsize * sizeof(*hash) + entries * sizeof(*entry));
60 if (!mem)
61 return NULL;
62 hash = mem;
63 entry = mem + hsize * sizeof(*hash);
64 memset(hash, 0, hsize * sizeof(*hash));
65
66 /* then populate it */
67 data = buf + entries * BLK_SIZE - BLK_SIZE;
68 blksize = bufsize - (data - buf);
69 while (data >= buf) {
70 unsigned int val = adler32(0, data, blksize);
71 i = HASH(val, hshift);
72 entry->ptr = data;
73 entry->val = val;
74 entry->next = hash[i];
75 hash[i] = entry++;
76 blksize = BLK_SIZE;
a310d434 77 data -= BLK_SIZE;
8e1454b5 78 }
a310d434 79
8e1454b5 80 return hash;
a310d434
NP
81}
82
fe474b58 83/* provide the size of the copy opcode given the block offset and size */
a310d434
NP
84#define COPYOP_SIZE(o, s) \
85 (!!(o & 0xff) + !!(o & 0xff00) + !!(o & 0xff0000) + !!(o & 0xff000000) + \
86 !!(s & 0xff) + !!(s & 0xff00) + 1)
87
fe474b58
NP
88/* the maximum size for any opcode */
89#define MAX_OP_SIZE COPYOP_SIZE(0xffffffff, 0xffffffff)
90
a310d434
NP
91void *diff_delta(void *from_buf, unsigned long from_size,
92 void *to_buf, unsigned long to_size,
75c42d8c
LT
93 unsigned long *delta_size,
94 unsigned long max_size)
a310d434 95{
8e1454b5
NP
96 unsigned int i, outpos, outsize, inscnt, hash_shift;
97 const unsigned char *ref_data, *ref_top, *data, *top;
98 unsigned char *out;
99 struct index *entry, **hash;
a310d434 100
8e1454b5 101 if (!from_size || !to_size)
a310d434 102 return NULL;
8e1454b5
NP
103 hash = delta_index(from_buf, from_size, &hash_shift);
104 if (!hash)
105 return NULL;
106
a310d434
NP
107 outpos = 0;
108 outsize = 8192;
fe474b58
NP
109 if (max_size && outsize >= max_size)
110 outsize = max_size + MAX_OP_SIZE + 1;
a310d434
NP
111 out = malloc(outsize);
112 if (!out) {
8e1454b5 113 free(hash);
a310d434
NP
114 return NULL;
115 }
116
e5e3a9d8
NP
117 ref_data = from_buf;
118 ref_top = from_buf + from_size;
a310d434
NP
119 data = to_buf;
120 top = to_buf + to_size;
121
122 /* store reference buffer size */
69a2d426
NP
123 out[outpos++] = from_size;
124 from_size >>= 7;
125 while (from_size) {
126 out[outpos - 1] |= 0x80;
127 out[outpos++] = from_size;
128 from_size >>= 7;
129 }
a310d434
NP
130
131 /* store target buffer size */
69a2d426
NP
132 out[outpos++] = to_size;
133 to_size >>= 7;
134 while (to_size) {
135 out[outpos - 1] |= 0x80;
136 out[outpos++] = to_size;
137 to_size >>= 7;
138 }
a310d434
NP
139
140 inscnt = 0;
a310d434 141
8e1454b5
NP
142 while (data < top) {
143 unsigned int moff = 0, msize = 0;
144 unsigned int blksize = MIN(top - data, BLK_SIZE);
145 unsigned int val = adler32(0, data, blksize);
146 i = HASH(val, hash_shift);
147 for (entry = hash[i]; entry; entry = entry->next) {
148 const unsigned char *ref = entry->ptr;
149 const unsigned char *src = data;
150 unsigned int ref_size = ref_top - ref;
151 if (entry->val != val)
152 continue;
153 if (ref_size > top - src)
154 ref_size = top - src;
155 while (ref_size && *src++ == *ref) {
156 ref++;
157 ref_size--;
158 }
159 ref_size = ref - entry->ptr;
160 if (ref_size > msize) {
161 /* this is our best match so far */
162 moff = entry->ptr - ref_data;
163 msize = ref_size;
164 if (msize >= 0x10000) {
165 msize = 0x10000;
166 break;
a310d434
NP
167 }
168 }
169 }
170
171 if (!msize || msize < COPYOP_SIZE(moff, msize)) {
172 if (!inscnt)
173 outpos++;
174 out[outpos++] = *data++;
175 inscnt++;
176 if (inscnt == 0x7f) {
177 out[outpos - inscnt - 1] = inscnt;
178 inscnt = 0;
179 }
180 } else {
8e1454b5
NP
181 unsigned char *op;
182
a310d434
NP
183 if (inscnt) {
184 out[outpos - inscnt - 1] = inscnt;
185 inscnt = 0;
186 }
187
188 data += msize;
8e1454b5 189 op = out + outpos++;
a310d434
NP
190 i = 0x80;
191
192 if (moff & 0xff) { out[outpos++] = moff; i |= 0x01; }
193 moff >>= 8;
194 if (moff & 0xff) { out[outpos++] = moff; i |= 0x02; }
195 moff >>= 8;
196 if (moff & 0xff) { out[outpos++] = moff; i |= 0x04; }
197 moff >>= 8;
198 if (moff & 0xff) { out[outpos++] = moff; i |= 0x08; }
199
200 if (msize & 0xff) { out[outpos++] = msize; i |= 0x10; }
201 msize >>= 8;
202 if (msize & 0xff) { out[outpos++] = msize; i |= 0x20; }
203
8e1454b5 204 *op = i;
a310d434
NP
205 }
206
fe474b58 207 if (outpos >= outsize - MAX_OP_SIZE) {
a310d434
NP
208 void *tmp = out;
209 outsize = outsize * 3 / 2;
fe474b58
NP
210 if (max_size && outsize >= max_size)
211 outsize = max_size + MAX_OP_SIZE + 1;
212 if (max_size && outpos > max_size)
213 out = NULL;
214 else
215 out = realloc(out, outsize);
a310d434
NP
216 if (!out) {
217 free(tmp);
8e1454b5 218 free(hash);
a310d434
NP
219 return NULL;
220 }
221 }
222 }
223
224 if (inscnt)
225 out[outpos - inscnt - 1] = inscnt;
226
8e1454b5 227 free(hash);
a310d434
NP
228 *delta_size = outpos;
229 return out;
230}