diff-delta.c

   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>
  22 #include <string.h>
  23 #include "delta.h"
  24
  25 #include "git-compat-util.h"
  26
  27 /* maximum hash entry list for the same hash bucket */
  28 #define HASH_LIMIT 64
  29
  30 #define RABIN_SHIFT 23
  31 #define RABIN_WINDOW 16
  32
  33 static const unsigned int T[256] = {
  34         0x00000000, 0xab59b4d1, 0x56b369a2, 0xfdeadd73, 0x063f6795, 0xad66d344,
  35         0x508c0e37, 0xfbd5bae6, 0x0c7ecf2a, 0xa7277bfb, 0x5acda688, 0xf1941259,
  36         0x0a41a8bf, 0xa1181c6e, 0x5cf2c11d, 0xf7ab75cc, 0x18fd9e54, 0xb3a42a85,
  37         0x4e4ef7f6, 0xe5174327, 0x1ec2f9c1, 0xb59b4d10, 0x48719063, 0xe32824b2,
  38         0x1483517e, 0xbfdae5af, 0x423038dc, 0xe9698c0d, 0x12bc36eb, 0xb9e5823a,
  39         0x440f5f49, 0xef56eb98, 0x31fb3ca8, 0x9aa28879, 0x6748550a, 0xcc11e1db,
  40         0x37c45b3d, 0x9c9defec, 0x6177329f, 0xca2e864e, 0x3d85f382, 0x96dc4753,
  41         0x6b369a20, 0xc06f2ef1, 0x3bba9417, 0x90e320c6, 0x6d09fdb5, 0xc6504964,
  42         0x2906a2fc, 0x825f162d, 0x7fb5cb5e, 0xd4ec7f8f, 0x2f39c569, 0x846071b8,
  43         0x798aaccb, 0xd2d3181a, 0x25786dd6, 0x8e21d907, 0x73cb0474, 0xd892b0a5,
  44         0x23470a43, 0x881ebe92, 0x75f463e1, 0xdeadd730, 0x63f67950, 0xc8afcd81,
  45         0x354510f2, 0x9e1ca423, 0x65c91ec5, 0xce90aa14, 0x337a7767, 0x9823c3b6,
  46         0x6f88b67a, 0xc4d102ab, 0x393bdfd8, 0x92626b09, 0x69b7d1ef, 0xc2ee653e,
  47         0x3f04b84d, 0x945d0c9c, 0x7b0be704, 0xd05253d5, 0x2db88ea6, 0x86e13a77,
  48         0x7d348091, 0xd66d3440, 0x2b87e933, 0x80de5de2, 0x7775282e, 0xdc2c9cff,
  49         0x21c6418c, 0x8a9ff55d, 0x714a4fbb, 0xda13fb6a, 0x27f92619, 0x8ca092c8,
  50         0x520d45f8, 0xf954f129, 0x04be2c5a, 0xafe7988b, 0x5432226d, 0xff6b96bc,
  51         0x02814bcf, 0xa9d8ff1e, 0x5e738ad2, 0xf52a3e03, 0x08c0e370, 0xa39957a1,
  52         0x584ced47, 0xf3155996, 0x0eff84e5, 0xa5a63034, 0x4af0dbac, 0xe1a96f7d,
  53         0x1c43b20e, 0xb71a06df, 0x4ccfbc39, 0xe79608e8, 0x1a7cd59b, 0xb125614a,
  54         0x468e1486, 0xedd7a057, 0x103d7d24, 0xbb64c9f5, 0x40b17313, 0xebe8c7c2,
  55         0x16021ab1, 0xbd5bae60, 0x6cb54671, 0xc7ecf2a0, 0x3a062fd3, 0x915f9b02,
  56         0x6a8a21e4, 0xc1d39535, 0x3c394846, 0x9760fc97, 0x60cb895b, 0xcb923d8a,
  57         0x3678e0f9, 0x9d215428, 0x66f4eece, 0xcdad5a1f, 0x3047876c, 0x9b1e33bd,
  58         0x7448d825, 0xdf116cf4, 0x22fbb187, 0x89a20556, 0x7277bfb0, 0xd92e0b61,
  59         0x24c4d612, 0x8f9d62c3, 0x7836170f, 0xd36fa3de, 0x2e857ead, 0x85dcca7c,
  60         0x7e09709a, 0xd550c44b, 0x28ba1938, 0x83e3ade9, 0x5d4e7ad9, 0xf617ce08,
  61         0x0bfd137b, 0xa0a4a7aa, 0x5b711d4c, 0xf028a99d, 0x0dc274ee, 0xa69bc03f,
  62         0x5130b5f3, 0xfa690122, 0x0783dc51, 0xacda6880, 0x570fd266, 0xfc5666b7,
  63         0x01bcbbc4, 0xaae50f15, 0x45b3e48d, 0xeeea505c, 0x13008d2f, 0xb85939fe,
  64         0x438c8318, 0xe8d537c9, 0x153feaba, 0xbe665e6b, 0x49cd2ba7, 0xe2949f76,
  65         0x1f7e4205, 0xb427f6d4, 0x4ff24c32, 0xe4abf8e3, 0x19412590, 0xb2189141,
  66         0x0f433f21, 0xa41a8bf0, 0x59f05683, 0xf2a9e252, 0x097c58b4, 0xa225ec65,
  67         0x5fcf3116, 0xf49685c7, 0x033df00b, 0xa86444da, 0x558e99a9, 0xfed72d78,
  68         0x0502979e, 0xae5b234f, 0x53b1fe3c, 0xf8e84aed, 0x17bea175, 0xbce715a4,
  69         0x410dc8d7, 0xea547c06, 0x1181c6e0, 0xbad87231, 0x4732af42, 0xec6b1b93,
  70         0x1bc06e5f, 0xb099da8e, 0x4d7307fd, 0xe62ab32c, 0x1dff09ca, 0xb6a6bd1b,
  71         0x4b4c6068, 0xe015d4b9, 0x3eb80389, 0x95e1b758, 0x680b6a2b, 0xc352defa,
  72         0x3887641c, 0x93ded0cd, 0x6e340dbe, 0xc56db96f, 0x32c6cca3, 0x999f7872,
  73         0x6475a501, 0xcf2c11d0, 0x34f9ab36, 0x9fa01fe7, 0x624ac294, 0xc9137645,
  74         0x26459ddd, 0x8d1c290c, 0x70f6f47f, 0xdbaf40ae, 0x207afa48, 0x8b234e99,
  75         0x76c993ea, 0xdd90273b, 0x2a3b52f7, 0x8162e626, 0x7c883b55, 0xd7d18f84,
  76         0x2c043562, 0x875d81b3, 0x7ab75cc0, 0xd1eee811
  77 };
  78
  79 static const unsigned int U[256] = {
  80         0x00000000, 0x7eb5200d, 0x5633f4cb, 0x2886d4c6, 0x073e5d47, 0x798b7d4a,
  81         0x510da98c, 0x2fb88981, 0x0e7cba8e, 0x70c99a83, 0x584f4e45, 0x26fa6e48,
  82         0x0942e7c9, 0x77f7c7c4, 0x5f711302, 0x21c4330f, 0x1cf9751c, 0x624c5511,
  83         0x4aca81d7, 0x347fa1da, 0x1bc7285b, 0x65720856, 0x4df4dc90, 0x3341fc9d,
  84         0x1285cf92, 0x6c30ef9f, 0x44b63b59, 0x3a031b54, 0x15bb92d5, 0x6b0eb2d8,
  85         0x4388661e, 0x3d3d4613, 0x39f2ea38, 0x4747ca35, 0x6fc11ef3, 0x11743efe,
  86         0x3eccb77f, 0x40799772, 0x68ff43b4, 0x164a63b9, 0x378e50b6, 0x493b70bb,
  87         0x61bda47d, 0x1f088470, 0x30b00df1, 0x4e052dfc, 0x6683f93a, 0x1836d937,
  88         0x250b9f24, 0x5bbebf29, 0x73386bef, 0x0d8d4be2, 0x2235c263, 0x5c80e26e,
  89         0x740636a8, 0x0ab316a5, 0x2b7725aa, 0x55c205a7, 0x7d44d161, 0x03f1f16c,
  90         0x2c4978ed, 0x52fc58e0, 0x7a7a8c26, 0x04cfac2b, 0x73e5d470, 0x0d50f47d,
  91         0x25d620bb, 0x5b6300b6, 0x74db8937, 0x0a6ea93a, 0x22e87dfc, 0x5c5d5df1,
  92         0x7d996efe, 0x032c4ef3, 0x2baa9a35, 0x551fba38, 0x7aa733b9, 0x041213b4,
  93         0x2c94c772, 0x5221e77f, 0x6f1ca16c, 0x11a98161, 0x392f55a7, 0x479a75aa,
  94         0x6822fc2b, 0x1697dc26, 0x3e1108e0, 0x40a428ed, 0x61601be2, 0x1fd53bef,
  95         0x3753ef29, 0x49e6cf24, 0x665e46a5, 0x18eb66a8, 0x306db26e, 0x4ed89263,
  96         0x4a173e48, 0x34a21e45, 0x1c24ca83, 0x6291ea8e, 0x4d29630f, 0x339c4302,
  97         0x1b1a97c4, 0x65afb7c9, 0x446b84c6, 0x3adea4cb, 0x1258700d, 0x6ced5000,
  98         0x4355d981, 0x3de0f98c, 0x15662d4a, 0x6bd30d47, 0x56ee4b54, 0x285b6b59,
  99         0x00ddbf9f, 0x7e689f92, 0x51d01613, 0x2f65361e, 0x07e3e2d8, 0x7956c2d5,
 100         0x5892f1da, 0x2627d1d7, 0x0ea10511, 0x7014251c, 0x5facac9d, 0x21198c90,
 101         0x099f5856, 0x772a785b, 0x4c921c31, 0x32273c3c, 0x1aa1e8fa, 0x6414c8f7,
 102         0x4bac4176, 0x3519617b, 0x1d9fb5bd, 0x632a95b0, 0x42eea6bf, 0x3c5b86b2,
 103         0x14dd5274, 0x6a687279, 0x45d0fbf8, 0x3b65dbf5, 0x13e30f33, 0x6d562f3e,
 104         0x506b692d, 0x2ede4920, 0x06589de6, 0x78edbdeb, 0x5755346a, 0x29e01467,
 105         0x0166c0a1, 0x7fd3e0ac, 0x5e17d3a3, 0x20a2f3ae, 0x08242768, 0x76910765,
 106         0x59298ee4, 0x279caee9, 0x0f1a7a2f, 0x71af5a22, 0x7560f609, 0x0bd5d604,
 107         0x235302c2, 0x5de622cf, 0x725eab4e, 0x0ceb8b43, 0x246d5f85, 0x5ad87f88,
 108         0x7b1c4c87, 0x05a96c8a, 0x2d2fb84c, 0x539a9841, 0x7c2211c0, 0x029731cd,
 109         0x2a11e50b, 0x54a4c506, 0x69998315, 0x172ca318, 0x3faa77de, 0x411f57d3,
 110         0x6ea7de52, 0x1012fe5f, 0x38942a99, 0x46210a94, 0x67e5399b, 0x19501996,
 111         0x31d6cd50, 0x4f63ed5d, 0x60db64dc, 0x1e6e44d1, 0x36e89017, 0x485db01a,
 112         0x3f77c841, 0x41c2e84c, 0x69443c8a, 0x17f11c87, 0x38499506, 0x46fcb50b,
 113         0x6e7a61cd, 0x10cf41c0, 0x310b72cf, 0x4fbe52c2, 0x67388604, 0x198da609,
 114         0x36352f88, 0x48800f85, 0x6006db43, 0x1eb3fb4e, 0x238ebd5d, 0x5d3b9d50,
 115         0x75bd4996, 0x0b08699b, 0x24b0e01a, 0x5a05c017, 0x728314d1, 0x0c3634dc,
 116         0x2df207d3, 0x534727de, 0x7bc1f318, 0x0574d315, 0x2acc5a94, 0x54797a99,
 117         0x7cffae5f, 0x024a8e52, 0x06852279, 0x78300274, 0x50b6d6b2, 0x2e03f6bf,
 118         0x01bb7f3e, 0x7f0e5f33, 0x57888bf5, 0x293dabf8, 0x08f998f7, 0x764cb8fa,
 119         0x5eca6c3c, 0x207f4c31, 0x0fc7c5b0, 0x7172e5bd, 0x59f4317b, 0x27411176,
 120         0x1a7c5765, 0x64c97768, 0x4c4fa3ae, 0x32fa83a3, 0x1d420a22, 0x63f72a2f,
 121         0x4b71fee9, 0x35c4dee4, 0x1400edeb, 0x6ab5cde6, 0x42331920, 0x3c86392d,
 122         0x133eb0ac, 0x6d8b90a1, 0x450d4467, 0x3bb8646a
 123 };
 124
 125 struct index_entry {
 126         const unsigned char *ptr;
 127         unsigned int val;
 128         struct index_entry *next;
 129 };
 130
 131 struct delta_index {
 132         const void *src_buf;
 133         unsigned long src_size;
 134         unsigned int hash_mask;
 135         struct index_entry *hash[FLEX_ARRAY];
 136 };
 137
 138 struct delta_index * create_delta_index(const void *buf, unsigned long bufsize)
 139 {
 140         unsigned int i, hsize, hmask, entries, prev_val, *hash_count;
 141         const unsigned char *data, *buffer = buf;
 142         struct delta_index *index;
 143         struct index_entry *entry, **hash;
 144         void *mem;
 145         unsigned long memsize;
 146
 147         if (!buf || !bufsize)
 148                 return NULL;
 149
 150         /* Determine index hash size.  Note that indexing skips the
 151            first byte to allow for optimizing the Rabin's polynomial
 152            initialization in create_delta(). */
 153         entries = (bufsize - 1)  / RABIN_WINDOW;
 154         hsize = entries / 4;
 155         for (i = 4; (1u << i) < hsize && i < 31; i++);
 156         hsize = 1 << i;
 157         hmask = hsize - 1;
 158
 159         /* allocate lookup index */
 160         memsize = sizeof(*index) +
 161                   sizeof(*hash) * hsize +
 162                   sizeof(*entry) * entries;
 163         mem = malloc(memsize);
 164         if (!mem)
 165                 return NULL;
 166         index = mem;
 167         mem = index + 1;
 168         hash = mem;
 169         mem = hash + hsize;
 170         entry = mem;
 171
 172         index->src_buf = buf;
 173         index->src_size = bufsize;
 174         index->hash_mask = hmask;
 175         memset(hash, 0, hsize * sizeof(*hash));
 176
 177         /* allocate an array to count hash entries */
 178         hash_count = calloc(hsize, sizeof(*hash_count));
 179         if (!hash_count) {
 180                 free(index);
 181                 return NULL;
 182         }
 183
 184         /* then populate the index */
 185         prev_val = ~0;
 186         for (data = buffer + entries * RABIN_WINDOW - RABIN_WINDOW;
 187              data >= buffer;
 188              data -= RABIN_WINDOW) {
 189                 unsigned int val = 0;
 190                 for (i = 1; i <= RABIN_WINDOW; i++)
 191                         val = ((val << 8) | data[i]) ^ T[val >> RABIN_SHIFT];
 192                 if (val == prev_val) {
 193                         /* keep the lowest of consecutive identical blocks */
 194                         entry[-1].ptr = data + RABIN_WINDOW;
 195                 } else {
 196                         prev_val = val;
 197                         i = val & hmask;
 198                         entry->ptr = data + RABIN_WINDOW;
 199                         entry->val = val;
 200                         entry->next = hash[i];
 201                         hash[i] = entry++;
 202                         hash_count[i]++;
 203                 }
 204         }
 205
 206         /*
 207          * Determine a limit on the number of entries in the same hash
 208          * bucket.  This guards us against pathological data sets causing
 209          * really bad hash distribution with most entries in the same hash
 210          * bucket that would bring us to O(m*n) computing costs (m and n
 211          * corresponding to reference and target buffer sizes).
 212          *
 213          * Make sure none of the hash buckets has more entries than
 214          * we're willing to test.  Otherwise we cull the entry list
 215          * uniformly to still preserve a good repartition across
 216          * the reference buffer.
 217          */
 218         for (i = 0; i < hsize; i++) {
 219                 if (hash_count[i] < HASH_LIMIT)
 220                         continue;
 221                 entry = hash[i];
 222                 do {
 223                         struct index_entry *keep = entry;
 224                         int skip = hash_count[i] / HASH_LIMIT / 2;
 225                         do {
 226                                 entry = entry->next;
 227                         } while(--skip && entry);
 228                         keep->next = entry;
 229                 } while(entry);
 230         }
 231         free(hash_count);
 232
 233         return index;
 234 }
 235
 236 void free_delta_index(struct delta_index *index)
 237 {
 238         free(index);
 239 }
 240
 241 /*
 242  * The maximum size for any opcode sequence, including the initial header
 243  * plus Rabin window plus biggest copy.
 244  */
 245 #define MAX_OP_SIZE     (5 + 5 + 1 + RABIN_WINDOW + 7)
 246
 247 void *
 248 create_delta(const struct delta_index *index,
 249              const void *trg_buf, unsigned long trg_size,
 250              unsigned long *delta_size, unsigned long max_size)
 251 {
 252         unsigned int i, outpos, outsize, val;
 253         int inscnt;
 254         const unsigned char *ref_data, *ref_top, *data, *top;
 255         unsigned char *out;
 256
 257         if (!trg_buf || !trg_size)
 258                 return NULL;
 259
 260         outpos = 0;
 261         outsize = 8192;
 262         if (max_size && outsize >= max_size)
 263                 outsize = max_size + MAX_OP_SIZE + 1;
 264         out = malloc(outsize);
 265         if (!out)
 266                 return NULL;
 267
 268         /* store reference buffer size */
 269         i = index->src_size;
 270         while (i >= 0x80) {
 271                 out[outpos++] = i | 0x80;
 272                 i >>= 7;
 273         }
 274         out[outpos++] = i;
 275
 276         /* store target buffer size */
 277         i = trg_size;
 278         while (i >= 0x80) {
 279                 out[outpos++] = i | 0x80;
 280                 i >>= 7;
 281         }
 282         out[outpos++] = i;
 283
 284         ref_data = index->src_buf;
 285         ref_top = ref_data + index->src_size;
 286         data = trg_buf;
 287         top = (const unsigned char *) trg_buf + trg_size;
 288
 289         outpos++;
 290         val = 0;
 291         for (i = 0; i < RABIN_WINDOW && data < top; i++, data++) {
 292                 out[outpos++] = *data;
 293                 val = ((val << 8) | *data) ^ T[val >> RABIN_SHIFT];
 294         }
 295         inscnt = i;
 296
 297         while (data < top) {
 298                 unsigned int moff = 0, msize = 0;
 299                 struct index_entry *entry;
 300                 val ^= U[data[-RABIN_WINDOW]];
 301                 val = ((val << 8) | *data) ^ T[val >> RABIN_SHIFT];
 302                 i = val & index->hash_mask;
 303                 for (entry = index->hash[i]; entry; entry = entry->next) {
 304                         const unsigned char *ref = entry->ptr;
 305                         const unsigned char *src = data;
 306                         unsigned int ref_size = ref_top - ref;
 307                         if (entry->val != val)
 308                                 continue;
 309                         if (ref_size > top - src)
 310                                 ref_size = top - src;
 311                         if (ref_size > 0x10000)
 312                                 ref_size = 0x10000;
 313                         if (ref_size <= msize)
 314                                 break;
 315                         while (ref_size-- && *src++ == *ref)
 316                                 ref++;
 317                         if (msize < ref - entry->ptr) {
 318                                 /* this is our best match so far */
 319                                 msize = ref - entry->ptr;
 320                                 moff = entry->ptr - ref_data;
 321                         }
 322                 }
 323
 324                 if (msize < 4) {
 325                         if (!inscnt)
 326                                 outpos++;
 327                         out[outpos++] = *data++;
 328                         inscnt++;
 329                         if (inscnt == 0x7f) {
 330                                 out[outpos - inscnt - 1] = inscnt;
 331                                 inscnt = 0;
 332                         }
 333                 } else {
 334                         unsigned char *op;
 335
 336                         if (msize >= RABIN_WINDOW) {
 337                                 const unsigned char *sk;
 338                                 sk = data + msize - RABIN_WINDOW;
 339                                 val = 0;
 340                                 for (i = 0; i < RABIN_WINDOW; i++)
 341                                         val = ((val << 8) | *sk++) ^ T[val >> RABIN_SHIFT];
 342                         } else {
 343                                 const unsigned char *sk = data + 1;
 344                                 for (i = 1; i < msize; i++) {
 345                                         val ^= U[sk[-RABIN_WINDOW]];
 346                                         val = ((val << 8) | *sk++) ^ T[val >> RABIN_SHIFT];
 347                                 }
 348                         }
 349
 350                         if (inscnt) {
 351                                 while (moff && ref_data[moff-1] == data[-1]) {
 352                                         if (msize == 0x10000)
 353                                                 break;
 354                                         /* we can match one byte back */
 355                                         msize++;
 356                                         moff--;
 357                                         data--;
 358                                         outpos--;
 359                                         if (--inscnt)
 360                                                 continue;
 361                                         outpos--;  /* remove count slot */
 362                                         inscnt--;  /* make it -1 */
 363                                         break;
 364                                 }
 365                                 out[outpos - inscnt - 1] = inscnt;
 366                                 inscnt = 0;
 367                         }
 368
 369                         data += msize;
 370                         op = out + outpos++;
 371                         i = 0x80;
 372
 373                         if (moff & 0xff) { out[outpos++] = moff; i |= 0x01; }
 374                         moff >>= 8;
 375                         if (moff & 0xff) { out[outpos++] = moff; i |= 0x02; }
 376                         moff >>= 8;
 377                         if (moff & 0xff) { out[outpos++] = moff; i |= 0x04; }
 378                         moff >>= 8;
 379                         if (moff & 0xff) { out[outpos++] = moff; i |= 0x08; }
 380
 381                         if (msize & 0xff) { out[outpos++] = msize; i |= 0x10; }
 382                         msize >>= 8;
 383                         if (msize & 0xff) { out[outpos++] = msize; i |= 0x20; }
 384
 385                         *op = i;
 386                 }
 387
 388                 if (outpos >= outsize - MAX_OP_SIZE) {
 389                         void *tmp = out;
 390                         outsize = outsize * 3 / 2;
 391                         if (max_size && outsize >= max_size)
 392                                 outsize = max_size + MAX_OP_SIZE + 1;
 393                         if (max_size && outpos > max_size)
 394                                 break;
 395                         out = xrealloc(out, outsize);
 396                         if (!out) {
 397                                 free(tmp);
 398                                 return NULL;
 399                         }
 400                 }
 401         }
 402
 403         if (inscnt)
 404                 out[outpos - inscnt - 1] = inscnt;
 405
 406         if (max_size && outpos > max_size) {
 407                 free(out);
 408                 return NULL;
 409         }
 410
 411         *delta_size = outpos;
 412         return out;
 413 }