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#include "git-compat-util.h"
22#include "delta.h"
23/* maximum hash entry list for the same hash bucket */
25#define HASH_LIMIT 64
26#define RABIN_SHIFT 23
28#define RABIN_WINDOW 16
29static const unsigned int T[256] = {
31 0x00000000, 0xab59b4d1, 0x56b369a2, 0xfdeadd73, 0x063f6795, 0xad66d344,
32 0x508c0e37, 0xfbd5bae6, 0x0c7ecf2a, 0xa7277bfb, 0x5acda688, 0xf1941259,
33 0x0a41a8bf, 0xa1181c6e, 0x5cf2c11d, 0xf7ab75cc, 0x18fd9e54, 0xb3a42a85,
34 0x4e4ef7f6, 0xe5174327, 0x1ec2f9c1, 0xb59b4d10, 0x48719063, 0xe32824b2,
35 0x1483517e, 0xbfdae5af, 0x423038dc, 0xe9698c0d, 0x12bc36eb, 0xb9e5823a,
36 0x440f5f49, 0xef56eb98, 0x31fb3ca8, 0x9aa28879, 0x6748550a, 0xcc11e1db,
37 0x37c45b3d, 0x9c9defec, 0x6177329f, 0xca2e864e, 0x3d85f382, 0x96dc4753,
38 0x6b369a20, 0xc06f2ef1, 0x3bba9417, 0x90e320c6, 0x6d09fdb5, 0xc6504964,
39 0x2906a2fc, 0x825f162d, 0x7fb5cb5e, 0xd4ec7f8f, 0x2f39c569, 0x846071b8,
40 0x798aaccb, 0xd2d3181a, 0x25786dd6, 0x8e21d907, 0x73cb0474, 0xd892b0a5,
41 0x23470a43, 0x881ebe92, 0x75f463e1, 0xdeadd730, 0x63f67950, 0xc8afcd81,
42 0x354510f2, 0x9e1ca423, 0x65c91ec5, 0xce90aa14, 0x337a7767, 0x9823c3b6,
43 0x6f88b67a, 0xc4d102ab, 0x393bdfd8, 0x92626b09, 0x69b7d1ef, 0xc2ee653e,
44 0x3f04b84d, 0x945d0c9c, 0x7b0be704, 0xd05253d5, 0x2db88ea6, 0x86e13a77,
45 0x7d348091, 0xd66d3440, 0x2b87e933, 0x80de5de2, 0x7775282e, 0xdc2c9cff,
46 0x21c6418c, 0x8a9ff55d, 0x714a4fbb, 0xda13fb6a, 0x27f92619, 0x8ca092c8,
47 0x520d45f8, 0xf954f129, 0x04be2c5a, 0xafe7988b, 0x5432226d, 0xff6b96bc,
48 0x02814bcf, 0xa9d8ff1e, 0x5e738ad2, 0xf52a3e03, 0x08c0e370, 0xa39957a1,
49 0x584ced47, 0xf3155996, 0x0eff84e5, 0xa5a63034, 0x4af0dbac, 0xe1a96f7d,
50 0x1c43b20e, 0xb71a06df, 0x4ccfbc39, 0xe79608e8, 0x1a7cd59b, 0xb125614a,
51 0x468e1486, 0xedd7a057, 0x103d7d24, 0xbb64c9f5, 0x40b17313, 0xebe8c7c2,
52 0x16021ab1, 0xbd5bae60, 0x6cb54671, 0xc7ecf2a0, 0x3a062fd3, 0x915f9b02,
53 0x6a8a21e4, 0xc1d39535, 0x3c394846, 0x9760fc97, 0x60cb895b, 0xcb923d8a,
54 0x3678e0f9, 0x9d215428, 0x66f4eece, 0xcdad5a1f, 0x3047876c, 0x9b1e33bd,
55 0x7448d825, 0xdf116cf4, 0x22fbb187, 0x89a20556, 0x7277bfb0, 0xd92e0b61,
56 0x24c4d612, 0x8f9d62c3, 0x7836170f, 0xd36fa3de, 0x2e857ead, 0x85dcca7c,
57 0x7e09709a, 0xd550c44b, 0x28ba1938, 0x83e3ade9, 0x5d4e7ad9, 0xf617ce08,
58 0x0bfd137b, 0xa0a4a7aa, 0x5b711d4c, 0xf028a99d, 0x0dc274ee, 0xa69bc03f,
59 0x5130b5f3, 0xfa690122, 0x0783dc51, 0xacda6880, 0x570fd266, 0xfc5666b7,
60 0x01bcbbc4, 0xaae50f15, 0x45b3e48d, 0xeeea505c, 0x13008d2f, 0xb85939fe,
61 0x438c8318, 0xe8d537c9, 0x153feaba, 0xbe665e6b, 0x49cd2ba7, 0xe2949f76,
62 0x1f7e4205, 0xb427f6d4, 0x4ff24c32, 0xe4abf8e3, 0x19412590, 0xb2189141,
63 0x0f433f21, 0xa41a8bf0, 0x59f05683, 0xf2a9e252, 0x097c58b4, 0xa225ec65,
64 0x5fcf3116, 0xf49685c7, 0x033df00b, 0xa86444da, 0x558e99a9, 0xfed72d78,
65 0x0502979e, 0xae5b234f, 0x53b1fe3c, 0xf8e84aed, 0x17bea175, 0xbce715a4,
66 0x410dc8d7, 0xea547c06, 0x1181c6e0, 0xbad87231, 0x4732af42, 0xec6b1b93,
67 0x1bc06e5f, 0xb099da8e, 0x4d7307fd, 0xe62ab32c, 0x1dff09ca, 0xb6a6bd1b,
68 0x4b4c6068, 0xe015d4b9, 0x3eb80389, 0x95e1b758, 0x680b6a2b, 0xc352defa,
69 0x3887641c, 0x93ded0cd, 0x6e340dbe, 0xc56db96f, 0x32c6cca3, 0x999f7872,
70 0x6475a501, 0xcf2c11d0, 0x34f9ab36, 0x9fa01fe7, 0x624ac294, 0xc9137645,
71 0x26459ddd, 0x8d1c290c, 0x70f6f47f, 0xdbaf40ae, 0x207afa48, 0x8b234e99,
72 0x76c993ea, 0xdd90273b, 0x2a3b52f7, 0x8162e626, 0x7c883b55, 0xd7d18f84,
73 0x2c043562, 0x875d81b3, 0x7ab75cc0, 0xd1eee811
74};
75static const unsigned int U[256] = {
77 0x00000000, 0x7eb5200d, 0x5633f4cb, 0x2886d4c6, 0x073e5d47, 0x798b7d4a,
78 0x510da98c, 0x2fb88981, 0x0e7cba8e, 0x70c99a83, 0x584f4e45, 0x26fa6e48,
79 0x0942e7c9, 0x77f7c7c4, 0x5f711302, 0x21c4330f, 0x1cf9751c, 0x624c5511,
80 0x4aca81d7, 0x347fa1da, 0x1bc7285b, 0x65720856, 0x4df4dc90, 0x3341fc9d,
81 0x1285cf92, 0x6c30ef9f, 0x44b63b59, 0x3a031b54, 0x15bb92d5, 0x6b0eb2d8,
82 0x4388661e, 0x3d3d4613, 0x39f2ea38, 0x4747ca35, 0x6fc11ef3, 0x11743efe,
83 0x3eccb77f, 0x40799772, 0x68ff43b4, 0x164a63b9, 0x378e50b6, 0x493b70bb,
84 0x61bda47d, 0x1f088470, 0x30b00df1, 0x4e052dfc, 0x6683f93a, 0x1836d937,
85 0x250b9f24, 0x5bbebf29, 0x73386bef, 0x0d8d4be2, 0x2235c263, 0x5c80e26e,
86 0x740636a8, 0x0ab316a5, 0x2b7725aa, 0x55c205a7, 0x7d44d161, 0x03f1f16c,
87 0x2c4978ed, 0x52fc58e0, 0x7a7a8c26, 0x04cfac2b, 0x73e5d470, 0x0d50f47d,
88 0x25d620bb, 0x5b6300b6, 0x74db8937, 0x0a6ea93a, 0x22e87dfc, 0x5c5d5df1,
89 0x7d996efe, 0x032c4ef3, 0x2baa9a35, 0x551fba38, 0x7aa733b9, 0x041213b4,
90 0x2c94c772, 0x5221e77f, 0x6f1ca16c, 0x11a98161, 0x392f55a7, 0x479a75aa,
91 0x6822fc2b, 0x1697dc26, 0x3e1108e0, 0x40a428ed, 0x61601be2, 0x1fd53bef,
92 0x3753ef29, 0x49e6cf24, 0x665e46a5, 0x18eb66a8, 0x306db26e, 0x4ed89263,
93 0x4a173e48, 0x34a21e45, 0x1c24ca83, 0x6291ea8e, 0x4d29630f, 0x339c4302,
94 0x1b1a97c4, 0x65afb7c9, 0x446b84c6, 0x3adea4cb, 0x1258700d, 0x6ced5000,
95 0x4355d981, 0x3de0f98c, 0x15662d4a, 0x6bd30d47, 0x56ee4b54, 0x285b6b59,
96 0x00ddbf9f, 0x7e689f92, 0x51d01613, 0x2f65361e, 0x07e3e2d8, 0x7956c2d5,
97 0x5892f1da, 0x2627d1d7, 0x0ea10511, 0x7014251c, 0x5facac9d, 0x21198c90,
98 0x099f5856, 0x772a785b, 0x4c921c31, 0x32273c3c, 0x1aa1e8fa, 0x6414c8f7,
99 0x4bac4176, 0x3519617b, 0x1d9fb5bd, 0x632a95b0, 0x42eea6bf, 0x3c5b86b2,
100 0x14dd5274, 0x6a687279, 0x45d0fbf8, 0x3b65dbf5, 0x13e30f33, 0x6d562f3e,
101 0x506b692d, 0x2ede4920, 0x06589de6, 0x78edbdeb, 0x5755346a, 0x29e01467,
102 0x0166c0a1, 0x7fd3e0ac, 0x5e17d3a3, 0x20a2f3ae, 0x08242768, 0x76910765,
103 0x59298ee4, 0x279caee9, 0x0f1a7a2f, 0x71af5a22, 0x7560f609, 0x0bd5d604,
104 0x235302c2, 0x5de622cf, 0x725eab4e, 0x0ceb8b43, 0x246d5f85, 0x5ad87f88,
105 0x7b1c4c87, 0x05a96c8a, 0x2d2fb84c, 0x539a9841, 0x7c2211c0, 0x029731cd,
106 0x2a11e50b, 0x54a4c506, 0x69998315, 0x172ca318, 0x3faa77de, 0x411f57d3,
107 0x6ea7de52, 0x1012fe5f, 0x38942a99, 0x46210a94, 0x67e5399b, 0x19501996,
108 0x31d6cd50, 0x4f63ed5d, 0x60db64dc, 0x1e6e44d1, 0x36e89017, 0x485db01a,
109 0x3f77c841, 0x41c2e84c, 0x69443c8a, 0x17f11c87, 0x38499506, 0x46fcb50b,
110 0x6e7a61cd, 0x10cf41c0, 0x310b72cf, 0x4fbe52c2, 0x67388604, 0x198da609,
111 0x36352f88, 0x48800f85, 0x6006db43, 0x1eb3fb4e, 0x238ebd5d, 0x5d3b9d50,
112 0x75bd4996, 0x0b08699b, 0x24b0e01a, 0x5a05c017, 0x728314d1, 0x0c3634dc,
113 0x2df207d3, 0x534727de, 0x7bc1f318, 0x0574d315, 0x2acc5a94, 0x54797a99,
114 0x7cffae5f, 0x024a8e52, 0x06852279, 0x78300274, 0x50b6d6b2, 0x2e03f6bf,
115 0x01bb7f3e, 0x7f0e5f33, 0x57888bf5, 0x293dabf8, 0x08f998f7, 0x764cb8fa,
116 0x5eca6c3c, 0x207f4c31, 0x0fc7c5b0, 0x7172e5bd, 0x59f4317b, 0x27411176,
117 0x1a7c5765, 0x64c97768, 0x4c4fa3ae, 0x32fa83a3, 0x1d420a22, 0x63f72a2f,
118 0x4b71fee9, 0x35c4dee4, 0x1400edeb, 0x6ab5cde6, 0x42331920, 0x3c86392d,
119 0x133eb0ac, 0x6d8b90a1, 0x450d4467, 0x3bb8646a
120};
121struct index_entry {
123 const unsigned char *ptr;
124 unsigned int val;
125 struct index_entry *next;
126};
127struct delta_index {
129 const void *src_buf;
130 unsigned long src_size;
131 unsigned int hash_mask;
132 struct index_entry *hash[FLEX_ARRAY];
133};
134struct delta_index * create_delta_index(const void *buf, unsigned long bufsize)
136{
137 unsigned int i, hsize, hmask, entries, prev_val, *hash_count;
138 const unsigned char *data, *buffer = buf;
139 struct delta_index *index;
140 struct index_entry *entry, **hash;
141 void *mem;
142 unsigned long memsize;
143 if (!buf || !bufsize)
145 return NULL;
146 /* Determine index hash size. Note that indexing skips the
148 first byte to allow for optimizing the Rabin's polynomial
149 initialization in create_delta(). */
150 entries = (bufsize - 1) / RABIN_WINDOW;
151 hsize = entries / 4;
152 for (i = 4; (1u << i) < hsize && i < 31; i++);
153 hsize = 1 << i;
154 hmask = hsize - 1;
155 /* allocate lookup index */
157 memsize = sizeof(*index) +
158 sizeof(*hash) * hsize +
159 sizeof(*entry) * entries;
160 mem = malloc(memsize);
161 if (!mem)
162 return NULL;
163 index = mem;
164 mem = index + 1;
165 hash = mem;
166 mem = hash + hsize;
167 entry = mem;
168 index->src_buf = buf;
170 index->src_size = bufsize;
171 index->hash_mask = hmask;
172 memset(hash, 0, hsize * sizeof(*hash));
173 /* allocate an array to count hash entries */
175 hash_count = calloc(hsize, sizeof(*hash_count));
176 if (!hash_count) {
177 free(index);
178 return NULL;
179 }
180 /* then populate the index */
182 prev_val = ~0;
183 for (data = buffer + entries * RABIN_WINDOW - RABIN_WINDOW;
184 data >= buffer;
185 data -= RABIN_WINDOW) {
186 unsigned int val = 0;
187 for (i = 1; i <= RABIN_WINDOW; i++)
188 val = ((val << 8) | data[i]) ^ T[val >> RABIN_SHIFT];
189 if (val == prev_val) {
190 /* keep the lowest of consecutive identical blocks */
191 entry[-1].ptr = data + RABIN_WINDOW;
192 } else {
193 prev_val = val;
194 i = val & hmask;
195 entry->ptr = data + RABIN_WINDOW;
196 entry->val = val;
197 entry->next = hash[i];
198 hash[i] = entry++;
199 hash_count[i]++;
200 }
201 }
202 /*
204 * Determine a limit on the number of entries in the same hash
205 * bucket. This guards us against pathological data sets causing
206 * really bad hash distribution with most entries in the same hash
207 * bucket that would bring us to O(m*n) computing costs (m and n
208 * corresponding to reference and target buffer sizes).
209 *
210 * Make sure none of the hash buckets has more entries than
211 * we're willing to test. Otherwise we cull the entry list
212 * uniformly to still preserve a good repartition across
213 * the reference buffer.
214 */
215 for (i = 0; i < hsize; i++) {
216 if (hash_count[i] < HASH_LIMIT)
217 continue;
218 entry = hash[i];
219 do {
220 struct index_entry *keep = entry;
221 int skip = hash_count[i] / HASH_LIMIT / 2;
222 do {
223 entry = entry->next;
224 } while(--skip && entry);
225 keep->next = entry;
226 } while(entry);
227 }
228 free(hash_count);
229 return index;
231}
232void free_delta_index(struct delta_index *index)
234{
235 free(index);
236}
237/*
239 * The maximum size for any opcode sequence, including the initial header
240 * plus Rabin window plus biggest copy.
241 */
242#define MAX_OP_SIZE (5 + 5 + 1 + RABIN_WINDOW + 7)
243void *
245create_delta(const struct delta_index *index,
246 const void *trg_buf, unsigned long trg_size,
247 unsigned long *delta_size, unsigned long max_size)
248{
249 unsigned int i, outpos, outsize, val;
250 int inscnt;
251 const unsigned char *ref_data, *ref_top, *data, *top;
252 unsigned char *out;
253 if (!trg_buf || !trg_size)
255 return NULL;
256 outpos = 0;
258 outsize = 8192;
259 if (max_size && outsize >= max_size)
260 outsize = max_size + MAX_OP_SIZE + 1;
261 out = malloc(outsize);
262 if (!out)
263 return NULL;
264 /* store reference buffer size */
266 i = index->src_size;
267 while (i >= 0x80) {
268 out[outpos++] = i | 0x80;
269 i >>= 7;
270 }
271 out[outpos++] = i;
272 /* store target buffer size */
274 i = trg_size;
275 while (i >= 0x80) {
276 out[outpos++] = i | 0x80;
277 i >>= 7;
278 }
279 out[outpos++] = i;
280 ref_data = index->src_buf;
282 ref_top = ref_data + index->src_size;
283 data = trg_buf;
284 top = (const unsigned char *) trg_buf + trg_size;
285 outpos++;
287 val = 0;
288 for (i = 0; i < RABIN_WINDOW && data < top; i++, data++) {
289 out[outpos++] = *data;
290 val = ((val << 8) | *data) ^ T[val >> RABIN_SHIFT];
291 }
292 inscnt = i;
293 while (data < top) {
295 unsigned int moff = 0, msize = 0;
296 struct index_entry *entry;
297 val ^= U[data[-RABIN_WINDOW]];
298 val = ((val << 8) | *data) ^ T[val >> RABIN_SHIFT];
299 i = val & index->hash_mask;
300 for (entry = index->hash[i]; entry; entry = entry->next) {
301 const unsigned char *ref = entry->ptr;
302 const unsigned char *src = data;
303 unsigned int ref_size = ref_top - ref;
304 if (entry->val != val)
305 continue;
306 if (ref_size > top - src)
307 ref_size = top - src;
308 if (ref_size > 0x10000)
309 ref_size = 0x10000;
310 if (ref_size <= msize)
311 break;
312 while (ref_size-- && *src++ == *ref)
313 ref++;
314 if (msize < ref - entry->ptr) {
315 /* this is our best match so far */
316 msize = ref - entry->ptr;
317 moff = entry->ptr - ref_data;
318 }
319 }
320 if (msize < 4) {
322 if (!inscnt)
323 outpos++;
324 out[outpos++] = *data++;
325 inscnt++;
326 if (inscnt == 0x7f) {
327 out[outpos - inscnt - 1] = inscnt;
328 inscnt = 0;
329 }
330 } else {
331 unsigned char *op;
332 if (msize >= RABIN_WINDOW) {
334 const unsigned char *sk;
335 sk = data + msize - RABIN_WINDOW;
336 val = 0;
337 for (i = 0; i < RABIN_WINDOW; i++)
338 val = ((val << 8) | *sk++) ^ T[val >> RABIN_SHIFT];
339 } else {
340 const unsigned char *sk = data + 1;
341 for (i = 1; i < msize; i++) {
342 val ^= U[sk[-RABIN_WINDOW]];
343 val = ((val << 8) | *sk++) ^ T[val >> RABIN_SHIFT];
344 }
345 }
346 if (inscnt) {
348 while (moff && ref_data[moff-1] == data[-1]) {
349 if (msize == 0x10000)
350 break;
351 /* we can match one byte back */
352 msize++;
353 moff--;
354 data--;
355 outpos--;
356 if (--inscnt)
357 continue;
358 outpos--; /* remove count slot */
359 inscnt--; /* make it -1 */
360 break;
361 }
362 out[outpos - inscnt - 1] = inscnt;
363 inscnt = 0;
364 }
365 data += msize;
367 op = out + outpos++;
368 i = 0x80;
369 if (moff & 0xff) { out[outpos++] = moff; i |= 0x01; }
371 moff >>= 8;
372 if (moff & 0xff) { out[outpos++] = moff; i |= 0x02; }
373 moff >>= 8;
374 if (moff & 0xff) { out[outpos++] = moff; i |= 0x04; }
375 moff >>= 8;
376 if (moff & 0xff) { out[outpos++] = moff; i |= 0x08; }
377 if (msize & 0xff) { out[outpos++] = msize; i |= 0x10; }
379 msize >>= 8;
380 if (msize & 0xff) { out[outpos++] = msize; i |= 0x20; }
381 *op = i;
383 }
384 if (outpos >= outsize - MAX_OP_SIZE) {
386 void *tmp = out;
387 outsize = outsize * 3 / 2;
388 if (max_size && outsize >= max_size)
389 outsize = max_size + MAX_OP_SIZE + 1;
390 if (max_size && outpos > max_size)
391 break;
392 out = xrealloc(out, outsize);
393 if (!out) {
394 free(tmp);
395 return NULL;
396 }
397 }
398 }
399 if (inscnt)
401 out[outpos - inscnt - 1] = inscnt;
402 if (max_size && outpos > max_size) {
404 free(out);
405 return NULL;
406 }
407 *delta_size = outpos;
409 return out;
410}