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, prev_val, *hash_count;
 140         const unsigned char *data, *buffer = buf;
 141         struct delta_index *index;
 142         struct index_entry *entry, **hash;
 143         void *mem;
 144         unsigned long memsize;
 145
 146         if (!buf || !bufsize)
 147                 return NULL;
 148
 149         /* Determine index hash size.  Note that indexing skips the
 150            first byte to allow for optimizing the rabin polynomial
 151            initialization in create_delta(). */
 152         entries = (bufsize - 1)  / RABIN_WINDOW;
 153         hsize = entries / 4;
 154         for (i = 4; (1 << i) < hsize && i < 31; i++);
 155         hsize = 1 << i;
 156         hmask = hsize - 1;
 157
 158         /* allocate lookup index */
 159         memsize = sizeof(*index) +
 160                   sizeof(*hash) * hsize +
 161                   sizeof(*entry) * entries;
 162         mem = malloc(memsize);
 163         if (!mem)
 164                 return NULL;
 165         index = mem;
 166         mem = index + 1;
 167         hash = mem;
 168         mem = hash + hsize;
 169         entry = mem;
 170
 171         index->src_buf = buf;
 172         index->src_size = bufsize;
 173         index->hash_mask = hmask;
 174         memset(hash, 0, hsize * sizeof(*hash));
 175
 176         /* allocate an array to count hash entries */
 177         hash_count = calloc(hsize, sizeof(*hash_count));
 178         if (!hash_count) {
 179                 free(index);
 180                 return NULL;
 181         }
 182
 183         /* then populate the index */
 184         prev_val = ~0;
 185         for (data = buffer + entries * RABIN_WINDOW - RABIN_WINDOW;
 186              data >= buffer;
 187              data -= RABIN_WINDOW) {
 188                 unsigned int val = 0;
 189                 for (i = 1; i <= RABIN_WINDOW; i++)
 190                         val = ((val << 8) | data[i]) ^ T[val >> RABIN_SHIFT];
 191                 if (val == prev_val) {
 192                         /* keep the lowest of consecutive identical blocks */
 193                         entry[-1].ptr = data + RABIN_WINDOW;
 194                 } else {
 195                         prev_val = val;
 196                         i = val & hmask;
 197                         entry->ptr = data + RABIN_WINDOW;
 198                         entry->val = val;
 199                         entry->next = hash[i];
 200                         hash[i] = entry++;
 201                         hash_count[i]++;
 202                         entries--;
 203                 }
 204         }
 205
 206         /*
 207          * Determine a limit on the number of entries in the same hash
 208          * bucket.  This guard us against patological 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         /* If we didn't use all hash entries, free the unused memory. */
 234         if (entries)
 235                 index = realloc(index, memsize - entries * sizeof(*entry));
 236
 237         return index;
 238 }
 239
 240 void free_delta_index(struct delta_index *index)
 241 {
 242         free(index);
 243 }
 244
 245 /*
 246  * The maximum size for any opcode sequence, including the initial header
 247  * plus rabin window plus biggest copy.
 248  */
 249 #define MAX_OP_SIZE     (5 + 5 + 1 + RABIN_WINDOW + 7)
 250
 251 void *
 252 create_delta(const struct delta_index *index,
 253              const void *trg_buf, unsigned long trg_size,
 254              unsigned long *delta_size, unsigned long max_size)
 255 {
 256         unsigned int i, outpos, outsize, val;
 257         int inscnt;
 258         const unsigned char *ref_data, *ref_top, *data, *top;
 259         unsigned char *out;
 260
 261         if (!trg_buf || !trg_size)
 262                 return NULL;
 263
 264         outpos = 0;
 265         outsize = 8192;
 266         if (max_size && outsize >= max_size)
 267                 outsize = max_size + MAX_OP_SIZE + 1;
 268         out = malloc(outsize);
 269         if (!out)
 270                 return NULL;
 271
 272         /* store reference buffer size */
 273         i = index->src_size;
 274         while (i >= 0x80) {
 275                 out[outpos++] = i | 0x80;
 276                 i >>= 7;
 277         }
 278         out[outpos++] = i;
 279
 280         /* store target buffer size */
 281         i = trg_size;
 282         while (i >= 0x80) {
 283                 out[outpos++] = i | 0x80;
 284                 i >>= 7;
 285         }
 286         out[outpos++] = i;
 287
 288         ref_data = index->src_buf;
 289         ref_top = ref_data + index->src_size;
 290         data = trg_buf;
 291         top = trg_buf + trg_size;
 292
 293         outpos++;
 294         val = 0;
 295         for (i = 0; i < RABIN_WINDOW && data < top; i++, data++) {
 296                 out[outpos++] = *data;
 297                 val = ((val << 8) | *data) ^ T[val >> RABIN_SHIFT];
 298         }
 299         inscnt = i;
 300
 301         while (data < top) {
 302                 unsigned int moff = 0, msize = 0;
 303                 struct index_entry *entry;
 304                 val ^= U[data[-RABIN_WINDOW]];
 305                 val = ((val << 8) | *data) ^ T[val >> RABIN_SHIFT];
 306                 i = val & index->hash_mask;
 307                 for (entry = index->hash[i]; entry; entry = entry->next) {
 308                         const unsigned char *ref = entry->ptr;
 309                         const unsigned char *src = data;
 310                         unsigned int ref_size = ref_top - ref;
 311                         if (entry->val != val)
 312                                 continue;
 313                         if (ref_size > top - src)
 314                                 ref_size = top - src;
 315                         if (ref_size > 0x10000)
 316                                 ref_size = 0x10000;
 317                         if (ref_size <= msize)
 318                                 break;
 319                         while (ref_size-- && *src++ == *ref)
 320                                 ref++;
 321                         if (msize < ref - entry->ptr) {
 322                                 /* this is our best match so far */
 323                                 msize = ref - entry->ptr;
 324                                 moff = entry->ptr - ref_data;
 325                         }
 326                 }
 327
 328                 if (msize < 4) {
 329                         if (!inscnt)
 330                                 outpos++;
 331                         out[outpos++] = *data++;
 332                         inscnt++;
 333                         if (inscnt == 0x7f) {
 334                                 out[outpos - inscnt - 1] = inscnt;
 335                                 inscnt = 0;
 336                         }
 337                 } else {
 338                         unsigned char *op;
 339
 340                         if (msize >= RABIN_WINDOW) {
 341                                 const unsigned char *sk;
 342                                 sk = data + msize - RABIN_WINDOW;
 343                                 val = 0;
 344                                 for (i = 0; i < RABIN_WINDOW; i++)
 345                                         val = ((val << 8) | *sk++) ^ T[val >> RABIN_SHIFT];
 346                         } else {
 347                                 const unsigned char *sk = data + 1;
 348                                 for (i = 1; i < msize; i++) {
 349                                         val ^= U[sk[-RABIN_WINDOW]];
 350                                         val = ((val << 8) | *sk++) ^ T[val >> RABIN_SHIFT];
 351                                 }
 352                         }
 353
 354                         if (inscnt) {
 355                                 while (moff && ref_data[moff-1] == data[-1]) {
 356                                         if (msize == 0x10000)
 357                                                 break;
 358                                         /* we can match one byte back */
 359                                         msize++;
 360                                         moff--;
 361                                         data--;
 362                                         outpos--;
 363                                         if (--inscnt)
 364                                                 continue;
 365                                         outpos--;  /* remove count slot */
 366                                         inscnt--;  /* make it -1 */
 367                                         break;
 368                                 }
 369                                 out[outpos - inscnt - 1] = inscnt;
 370                                 inscnt = 0;
 371                         }
 372
 373                         data += msize;
 374                         op = out + outpos++;
 375                         i = 0x80;
 376
 377                         if (moff & 0xff) { out[outpos++] = moff; i |= 0x01; }
 378                         moff >>= 8;
 379                         if (moff & 0xff) { out[outpos++] = moff; i |= 0x02; }
 380                         moff >>= 8;
 381                         if (moff & 0xff) { out[outpos++] = moff; i |= 0x04; }
 382                         moff >>= 8;
 383                         if (moff & 0xff) { out[outpos++] = moff; i |= 0x08; }
 384
 385                         if (msize & 0xff) { out[outpos++] = msize; i |= 0x10; }
 386                         msize >>= 8;
 387                         if (msize & 0xff) { out[outpos++] = msize; i |= 0x20; }
 388
 389                         *op = i;
 390                 }
 391
 392                 if (outpos >= outsize - MAX_OP_SIZE) {
 393                         void *tmp = out;
 394                         outsize = outsize * 3 / 2;
 395                         if (max_size && outsize >= max_size)
 396                                 outsize = max_size + MAX_OP_SIZE + 1;
 397                         if (max_size && outpos > max_size)
 398                                 break;
 399                         out = realloc(out, outsize);
 400                         if (!out) {
 401                                 free(tmp);
 402                                 return NULL;
 403                         }
 404                 }
 405         }
 406
 407         if (inscnt)
 408                 out[outpos - inscnt - 1] = inscnt;
 409
 410         if (max_size && outpos > max_size) {
 411                 free(out);
 412                 return NULL;
 413         }
 414
 415         *delta_size = outpos;
 416         return out;
 417 }