Andrew's git - gitweb.git/blob

   1/*
   2 * patch-delta.c:
   3 * recreate a buffer from a source and the delta produced by diff-delta.c
   4 *
   5 * (C) 2005 Nicolas Pitre <nico@fluxnic.net>
   6 *
   7 * This code is free software; you can redistribute it and/or modify
   8 * it under the terms of the GNU General Public License version 2 as
   9 * published by the Free Software Foundation.
  10 */
  11
  12#include "git-compat-util.h"
  13#include "delta.h"
  14
  15void *patch_delta(const void *src_buf, unsigned long src_size,
  16                  const void *delta_buf, unsigned long delta_size,
  17                  unsigned long *dst_size)
  18{
  19        const unsigned char *data, *top;
  20        unsigned char *dst_buf, *out, cmd;
  21        unsigned long size;
  22
  23        if (delta_size < DELTA_SIZE_MIN)
  24                return NULL;
  25
  26        data = delta_buf;
  27        top = (const unsigned char *) delta_buf + delta_size;
  28
  29        /* make sure the orig file size matches what we expect */
  30        size = get_delta_hdr_size(&data, top);
  31        if (size != src_size)
  32                return NULL;
  33
  34        /* now the result size */
  35        size = get_delta_hdr_size(&data, top);
  36        dst_buf = xmallocz(size);
  37
  38        out = dst_buf;
  39        while (data < top) {
  40                cmd = *data++;
  41                if (cmd & 0x80) {
  42                        unsigned long cp_off = 0, cp_size = 0;
  43#define PARSE_CP_PARAM(bit, var, shift) do { \
  44                        if (cmd & (bit)) { \
  45                                if (data >= top) \
  46                                        goto bad_length; \
  47                                var |= ((unsigned) *data++ << (shift)); \
  48                        } } while (0)
  49                        PARSE_CP_PARAM(0x01, cp_off, 0);
  50                        PARSE_CP_PARAM(0x02, cp_off, 8);
  51                        PARSE_CP_PARAM(0x04, cp_off, 16);
  52                        PARSE_CP_PARAM(0x08, cp_off, 24);
  53                        PARSE_CP_PARAM(0x10, cp_size, 0);
  54                        PARSE_CP_PARAM(0x20, cp_size, 8);
  55                        PARSE_CP_PARAM(0x40, cp_size, 16);
  56#undef PARSE_CP_PARAM
  57                        if (cp_size == 0) cp_size = 0x10000;
  58                        if (unsigned_add_overflows(cp_off, cp_size) ||
  59                            cp_off + cp_size > src_size ||
  60                            cp_size > size)
  61                                goto bad_length;
  62                        memcpy(out, (char *) src_buf + cp_off, cp_size);
  63                        out += cp_size;
  64                        size -= cp_size;
  65                } else if (cmd) {
  66                        if (cmd > size || cmd > top - data)
  67                                goto bad_length;
  68                        memcpy(out, data, cmd);
  69                        out += cmd;
  70                        data += cmd;
  71                        size -= cmd;
  72                } else {
  73                        /*
  74                         * cmd == 0 is reserved for future encoding
  75                         * extensions. In the mean time we must fail when
  76                         * encountering them (might be data corruption).
  77                         */
  78                        error("unexpected delta opcode 0");
  79                        goto bad;
  80                }
  81        }
  82
  83        /* sanity check */
  84        if (data != top || size != 0) {
  85                bad_length:
  86                error("delta replay has gone wild");
  87                bad:
  88                free(dst_buf);
  89                return NULL;
  90        }
  91
  92        *dst_size = out - dst_buf;
  93        return dst_buf;
  94}