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         chanode_t *head, *tail;
  88         int isize, nsize;
  89         chanode_t *ancur;
  90         chanode_t *sncur;
  91         int scurr;
  92 } chastore_t;
  93
  94 static void cha_init(chastore_t *cha, int isize, int icount)
  95 {
  96         cha->head = cha->tail = NULL;
  97         cha->isize = isize;
  98         cha->nsize = icount * isize;
  99         cha->ancur = cha->sncur = NULL;
 100         cha->scurr = 0;
 101 }
 102
 103 static void *cha_alloc(chastore_t *cha)
 104 {
 105         chanode_t *ancur;
 106         void *data;
 107
 108         ancur = cha->ancur;
 109         if (!ancur || ancur->icurr == cha->nsize) {
 110                 ancur = malloc(sizeof(chanode_t) + cha->nsize);
 111                 if (!ancur)
 112                         return NULL;
 113                 ancur->icurr = 0;
 114                 ancur->next = NULL;
 115                 if (cha->tail)
 116                         cha->tail->next = ancur;
 117                 if (!cha->head)
 118                         cha->head = ancur;
 119                 cha->tail = ancur;
 120                 cha->ancur = ancur;
 121         }
 122
 123         data = (void *)ancur + sizeof(chanode_t) + ancur->icurr;
 124         ancur->icurr += cha->isize;
 125         return data;
 126 }
 127
 128 static void cha_free(chastore_t *cha)
 129 {
 130         chanode_t *cur = cha->head;
 131         while (cur) {
 132                 chanode_t *tmp = cur;
 133                 cur = cur->next;
 134                 free(tmp);
 135         }
 136 }
 137
 138 typedef struct s_bdrecord {
 139         struct s_bdrecord *next;
 140         unsigned int fp;
 141         const unsigned char *ptr;
 142 } bdrecord_t;
 143
 144 typedef struct s_bdfile {
 145         const unsigned char *data, *top;
 146         chastore_t cha;
 147         unsigned int fphbits;
 148         bdrecord_t **fphash;
 149 } bdfile_t;
 150
 151 static int delta_prepare(const unsigned char *buf, int bufsize, bdfile_t *bdf)
 152 {
 153         unsigned int fphbits;
 154         int i, hsize;
 155         const unsigned char *base, *data, *top;
 156         bdrecord_t *brec;
 157         bdrecord_t **fphash;
 158
 159         fphbits = hashbits(bufsize / BLK_SIZE + 1);
 160         hsize = 1 << fphbits;
 161         fphash = malloc(hsize * sizeof(bdrecord_t *));
 162         if (!fphash)
 163                 return -1;
 164         for (i = 0; i < hsize; i++)
 165                 fphash[i] = NULL;
 166         cha_init(&bdf->cha, sizeof(bdrecord_t), hsize / 4 + 1);
 167
 168         bdf->data = data = base = buf;
 169         bdf->top = top = buf + bufsize;
 170         data += (bufsize / BLK_SIZE) * BLK_SIZE;
 171         if (data == top)
 172                 data -= BLK_SIZE;
 173
 174         for ( ; data >= base; data -= BLK_SIZE) {
 175                 brec = cha_alloc(&bdf->cha);
 176                 if (!brec) {
 177                         cha_free(&bdf->cha);
 178                         free(fphash);
 179                         return -1;
 180                 }
 181                 brec->fp = adler32(0, data, MIN(BLK_SIZE, top - data));
 182                 brec->ptr = data;
 183                 i = HASH(brec->fp, fphbits);
 184                 brec->next = fphash[i];
 185                 fphash[i] = brec;
 186         }
 187
 188         bdf->fphbits = fphbits;
 189         bdf->fphash = fphash;
 190
 191         return 0;
 192 }
 193
 194 static void delta_cleanup(bdfile_t *bdf)
 195 {
 196         free(bdf->fphash);
 197         cha_free(&bdf->cha);
 198 }
 199
 200 #define COPYOP_SIZE(o, s) \
 201     (!!(o & 0xff) + !!(o & 0xff00) + !!(o & 0xff0000) + !!(o & 0xff000000) + \
 202      !!(s & 0xff) + !!(s & 0xff00) + 1)
 203
 204 void *diff_delta(void *from_buf, unsigned long from_size,
 205                  void *to_buf, unsigned long to_size,
 206                  unsigned long *delta_size)
 207 {
 208         int i, outpos, outsize, inscnt, csize, msize, moff;
 209         unsigned int fp;
 210         const unsigned char *data, *top, *ptr1, *ptr2;
 211         unsigned char *out, *orig;
 212         bdrecord_t *brec;
 213         bdfile_t bdf;
 214
 215         if (!from_size || !to_size || delta_prepare(from_buf, from_size, &bdf))
 216                 return NULL;
 217
 218         outpos = 0;
 219         outsize = 8192;
 220         out = malloc(outsize);
 221         if (!out) {
 222                 delta_cleanup(&bdf);
 223                 return NULL;
 224         }
 225
 226         data = to_buf;
 227         top = to_buf + to_size;
 228
 229         /* store reference buffer size */
 230         orig = out + outpos++;
 231         *orig = i = 0;
 232         do {
 233                 if (from_size & 0xff) {
 234                         *orig |= (1 << i);
 235                         out[outpos++] = from_size;
 236                 }
 237                 i++;
 238                 from_size >>= 8;
 239         } while (from_size);
 240
 241         /* store target buffer size */
 242         orig = out + outpos++;
 243         *orig = i = 0;
 244         do {
 245                 if (to_size & 0xff) {
 246                         *orig |= (1 << i);
 247                         out[outpos++] = to_size;
 248                 }
 249                 i++;
 250                 to_size >>= 8;
 251         } while (to_size);
 252
 253         inscnt = 0;
 254         moff = 0;
 255         while (data < top) {
 256                 msize = 0;
 257                 fp = adler32(0, data, MIN(top - data, BLK_SIZE));
 258                 i = HASH(fp, bdf.fphbits);
 259                 for (brec = bdf.fphash[i]; brec; brec = brec->next) {
 260                         if (brec->fp == fp) {
 261                                 csize = bdf.top - brec->ptr;
 262                                 if (csize > top - data)
 263                                         csize = top - data;
 264                                 for (ptr1 = brec->ptr, ptr2 = data;
 265                                      csize && *ptr1 == *ptr2;
 266                                      csize--, ptr1++, ptr2++);
 267
 268                                 csize = ptr1 - brec->ptr;
 269                                 if (csize > msize) {
 270                                         moff = brec->ptr - bdf.data;
 271                                         msize = csize;
 272                                         if (msize >= 0x10000) {
 273                                                 msize = 0x10000;
 274                                                 break;
 275                                         }
 276                                 }
 277                         }
 278                 }
 279
 280                 if (!msize || msize < COPYOP_SIZE(moff, msize)) {
 281                         if (!inscnt)
 282                                 outpos++;
 283                         out[outpos++] = *data++;
 284                         inscnt++;
 285                         if (inscnt == 0x7f) {
 286                                 out[outpos - inscnt - 1] = inscnt;
 287                                 inscnt = 0;
 288                         }
 289                 } else {
 290                         if (inscnt) {
 291                                 out[outpos - inscnt - 1] = inscnt;
 292                                 inscnt = 0;
 293                         }
 294
 295                         data += msize;
 296                         orig = out + outpos++;
 297                         i = 0x80;
 298
 299                         if (moff & 0xff) { out[outpos++] = moff; i |= 0x01; }
 300                         moff >>= 8;
 301                         if (moff & 0xff) { out[outpos++] = moff; i |= 0x02; }
 302                         moff >>= 8;
 303                         if (moff & 0xff) { out[outpos++] = moff; i |= 0x04; }
 304                         moff >>= 8;
 305                         if (moff & 0xff) { out[outpos++] = moff; i |= 0x08; }
 306
 307                         if (msize & 0xff) { out[outpos++] = msize; i |= 0x10; }
 308                         msize >>= 8;
 309                         if (msize & 0xff) { out[outpos++] = msize; i |= 0x20; }
 310
 311                         *orig = i;
 312                 }
 313
 314                 /* next time around the largest possible output is 1 + 4 + 3 */
 315                 if (outpos > outsize - 8) {
 316                         void *tmp = out;
 317                         outsize = outsize * 3 / 2;
 318                         out = realloc(out, outsize);
 319                         if (!out) {
 320                                 free(tmp);
 321                                 delta_cleanup(&bdf);
 322                                 return NULL;
 323                         }
 324                 }
 325         }
 326
 327         if (inscnt)
 328                 out[outpos - inscnt - 1] = inscnt;
 329
 330         delta_cleanup(&bdf);
 331         *delta_size = outpos;
 332         return out;
 333 }