Andrew's git - gitweb.git/blob

   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        
  34static 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
  44typedef struct s_chanode {
  45        struct s_chanode *next;
  46        int icurr;
  47} chanode_t;
  48
  49typedef struct s_chastore {
  50        int isize, nsize;
  51        chanode_t *ancur;
  52} chastore_t;
  53
  54static 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
  61static 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
  81static 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
  91typedef struct s_bdrecord {
  92        struct s_bdrecord *next;
  93        unsigned int fp;
  94        const unsigned char *ptr;
  95} bdrecord_t;
  96
  97typedef struct s_bdfile {
  98        chastore_t cha;
  99        unsigned int fphbits;
 100        bdrecord_t **fphash;
 101} bdfile_t;
 102
 103static 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
 145static 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
 159void *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}