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