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 "delta.h"
  23
  24
  25 /* block size: min = 16, max = 64k, power of 2 */
  26 #define BLK_SIZE 16
  27
  28 #define MIN(a, b) ((a) < (b) ? (a) : (b))
  29
  30 #define GR_PRIME 0x9e370001
  31 #define HASH(v, b) (((unsigned int)(v) * GR_PRIME) >> (32 - (b)))
  32
  33 /* largest prime smaller than 65536 */
  34 #define BASE 65521
  35
  36 /* NMAX is the largest n such that 255n(n+1)/2 + (n+1)(BASE-1) <= 2^32-1 */
  37 #define NMAX 5552
  38
  39 #define DO1(buf, i)  { s1 += buf[i]; s2 += s1; }
  40 #define DO2(buf, i)  DO1(buf, i); DO1(buf, i + 1);
  41 #define DO4(buf, i)  DO2(buf, i); DO2(buf, i + 2);
  42 #define DO8(buf, i)  DO4(buf, i); DO4(buf, i + 4);
  43 #define DO16(buf)    DO8(buf, 0); DO8(buf, 8);
  44
  45 static unsigned int adler32(unsigned int adler, const unsigned char *buf, int len)
  46 {
  47         int k;
  48         unsigned int s1 = adler & 0xffff;
  49         unsigned int s2 = adler >> 16;
  50
  51         while (len > 0) {
  52                 k = MIN(len, NMAX);
  53                 len -= k;
  54                 while (k >= 16) {
  55                         DO16(buf);
  56                         buf += 16;
  57                         k -= 16;
  58                 }
  59                 if (k != 0)
  60                         do {
  61                                 s1 += *buf++;
  62                                 s2 += s1;
  63                         } while (--k);
  64                 s1 %= BASE;
  65                 s2 %= BASE;
  66         }
  67
  68         return (s2 << 16) | s1;
  69 }
  70
  71 static unsigned int hashbits(unsigned int size)
  72 {
  73         unsigned int val = 1, bits = 0;
  74         while (val < size && bits < 32) {
  75                 val <<= 1;
  76                 bits++;
  77         }
  78         return bits ? bits: 1;
  79 }
  80
  81 typedef struct s_chanode {
  82         struct s_chanode *next;
  83         int icurr;
  84 } chanode_t;
  85
  86 typedef struct s_chastore {
  87         int isize, nsize;
  88         chanode_t *ancur;
  89 } chastore_t;
  90
  91 static void cha_init(chastore_t *cha, int isize, int icount)
  92 {
  93         cha->isize = isize;
  94         cha->nsize = icount * isize;
  95         cha->ancur = NULL;
  96 }
  97
  98 static void *cha_alloc(chastore_t *cha)
  99 {
 100         chanode_t *ancur;
 101         void *data;
 102
 103         ancur = cha->ancur;
 104         if (!ancur || ancur->icurr == cha->nsize) {
 105                 ancur = malloc(sizeof(chanode_t) + cha->nsize);
 106                 if (!ancur)
 107                         return NULL;
 108                 ancur->icurr = 0;
 109                 ancur->next = cha->ancur;
 110                 cha->ancur = ancur;
 111         }
 112
 113         data = (void *)ancur + sizeof(chanode_t) + ancur->icurr;
 114         ancur->icurr += cha->isize;
 115         return data;
 116 }
 117
 118 static void cha_free(chastore_t *cha)
 119 {
 120         chanode_t *cur = cha->ancur;
 121         while (cur) {
 122                 chanode_t *tmp = cur;
 123                 cur = cur->next;
 124                 free(tmp);
 125         }
 126 }
 127
 128 typedef struct s_bdrecord {
 129         struct s_bdrecord *next;
 130         unsigned int fp;
 131         const unsigned char *ptr;
 132 } bdrecord_t;
 133
 134 typedef struct s_bdfile {
 135         chastore_t cha;
 136         unsigned int fphbits;
 137         bdrecord_t **fphash;
 138 } bdfile_t;
 139
 140 static int delta_prepare(const unsigned char *buf, int bufsize, bdfile_t *bdf)
 141 {
 142         unsigned int fphbits;
 143         int i, hsize;
 144         const unsigned char *data, *top;
 145         bdrecord_t *brec;
 146         bdrecord_t **fphash;
 147
 148         fphbits = hashbits(bufsize / BLK_SIZE + 1);
 149         hsize = 1 << fphbits;
 150         fphash = malloc(hsize * sizeof(bdrecord_t *));
 151         if (!fphash)
 152                 return -1;
 153         for (i = 0; i < hsize; i++)
 154                 fphash[i] = NULL;
 155         cha_init(&bdf->cha, sizeof(bdrecord_t), hsize / 4 + 1);
 156
 157         top = buf + bufsize;
 158         data = buf + (bufsize / BLK_SIZE) * BLK_SIZE;
 159         if (data == top)
 160                 data -= BLK_SIZE;
 161
 162         for ( ; data >= buf; data -= BLK_SIZE) {
 163                 brec = cha_alloc(&bdf->cha);
 164                 if (!brec) {
 165                         cha_free(&bdf->cha);
 166                         free(fphash);
 167                         return -1;
 168                 }
 169                 brec->fp = adler32(0, data, MIN(BLK_SIZE, top - data));
 170                 brec->ptr = data;
 171                 i = HASH(brec->fp, fphbits);
 172                 brec->next = fphash[i];
 173                 fphash[i] = brec;
 174         }
 175
 176         bdf->fphbits = fphbits;
 177         bdf->fphash = fphash;
 178
 179         return 0;
 180 }
 181
 182 static void delta_cleanup(bdfile_t *bdf)
 183 {
 184         free(bdf->fphash);
 185         cha_free(&bdf->cha);
 186 }
 187
 188 #define COPYOP_SIZE(o, s) \
 189     (!!(o & 0xff) + !!(o & 0xff00) + !!(o & 0xff0000) + !!(o & 0xff000000) + \
 190      !!(s & 0xff) + !!(s & 0xff00) + 1)
 191
 192 void *diff_delta(void *from_buf, unsigned long from_size,
 193                  void *to_buf, unsigned long to_size,
 194                  unsigned long *delta_size,
 195                  unsigned long max_size)
 196 {
 197         int i, outpos, outsize, inscnt, csize, msize, moff;
 198         unsigned int fp;
 199         const unsigned char *ref_data, *ref_top, *data, *top, *ptr1, *ptr2;
 200         unsigned char *out, *orig;
 201         bdrecord_t *brec;
 202         bdfile_t bdf;
 203
 204         if (!from_size || !to_size || delta_prepare(from_buf, from_size, &bdf))
 205                 return NULL;
 206
 207         outpos = 0;
 208         outsize = 8192;
 209         out = malloc(outsize);
 210         if (!out) {
 211                 delta_cleanup(&bdf);
 212                 return NULL;
 213         }
 214
 215         ref_data = from_buf;
 216         ref_top = from_buf + from_size;
 217         data = to_buf;
 218         top = to_buf + to_size;
 219
 220         /* store reference buffer size */
 221         out[outpos++] = from_size;
 222         from_size >>= 7;
 223         while (from_size) {
 224                 out[outpos - 1] |= 0x80;
 225                 out[outpos++] = from_size;
 226                 from_size >>= 7;
 227         }
 228
 229         /* store target buffer size */
 230         out[outpos++] = to_size;
 231         to_size >>= 7;
 232         while (to_size) {
 233                 out[outpos - 1] |= 0x80;
 234                 out[outpos++] = to_size;
 235                 to_size >>= 7;
 236         }
 237
 238         inscnt = 0;
 239         moff = 0;
 240         while (data < top) {
 241                 msize = 0;
 242                 fp = adler32(0, data, MIN(top - data, BLK_SIZE));
 243                 i = HASH(fp, bdf.fphbits);
 244                 for (brec = bdf.fphash[i]; brec; brec = brec->next) {
 245                         if (brec->fp == fp) {
 246                                 csize = ref_top - brec->ptr;
 247                                 if (csize > top - data)
 248                                         csize = top - data;
 249                                 for (ptr1 = brec->ptr, ptr2 = data;
 250                                      csize && *ptr1 == *ptr2;
 251                                      csize--, ptr1++, ptr2++);
 252
 253                                 csize = ptr1 - brec->ptr;
 254                                 if (csize > msize) {
 255                                         moff = brec->ptr - ref_data;
 256                                         msize = csize;
 257                                         if (msize >= 0x10000) {
 258                                                 msize = 0x10000;
 259                                                 break;
 260                                         }
 261                                 }
 262                         }
 263                 }
 264
 265                 if (!msize || msize < COPYOP_SIZE(moff, msize)) {
 266                         if (!inscnt)
 267                                 outpos++;
 268                         out[outpos++] = *data++;
 269                         inscnt++;
 270                         if (inscnt == 0x7f) {
 271                                 out[outpos - inscnt - 1] = inscnt;
 272                                 inscnt = 0;
 273                         }
 274                 } else {
 275                         if (inscnt) {
 276                                 out[outpos - inscnt - 1] = inscnt;
 277                                 inscnt = 0;
 278                         }
 279
 280                         data += msize;
 281                         orig = out + outpos++;
 282                         i = 0x80;
 283
 284                         if (moff & 0xff) { out[outpos++] = moff; i |= 0x01; }
 285                         moff >>= 8;
 286                         if (moff & 0xff) { out[outpos++] = moff; i |= 0x02; }
 287                         moff >>= 8;
 288                         if (moff & 0xff) { out[outpos++] = moff; i |= 0x04; }
 289                         moff >>= 8;
 290                         if (moff & 0xff) { out[outpos++] = moff; i |= 0x08; }
 291
 292                         if (msize & 0xff) { out[outpos++] = msize; i |= 0x10; }
 293                         msize >>= 8;
 294                         if (msize & 0xff) { out[outpos++] = msize; i |= 0x20; }
 295
 296                         *orig = i;
 297                 }
 298
 299                 if (max_size && outpos > max_size) {
 300                         free(out);
 301                         delta_cleanup(&bdf);
 302                         return NULL;
 303                 }
 304
 305                 /* next time around the largest possible output is 1 + 4 + 3 */
 306                 if (outpos > outsize - 8) {
 307                         void *tmp = out;
 308                         outsize = outsize * 3 / 2;
 309                         out = realloc(out, outsize);
 310                         if (!out) {
 311                                 free(tmp);
 312                                 delta_cleanup(&bdf);
 313                                 return NULL;
 314                         }
 315                 }
 316         }
 317
 318         if (inscnt)
 319                 out[outpos - inscnt - 1] = inscnt;
 320
 321         delta_cleanup(&bdf);
 322         *delta_size = outpos;
 323         return out;
 324 }