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