patch-delta.c

   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@cam.org>
   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 <stdlib.h>
  13 #include <string.h>
  14 #include "delta.h"
  15
  16 void *patch_delta(void *src_buf, unsigned long src_size,
  17                   void *delta_buf, unsigned long delta_size,
  18                   unsigned long *dst_size)
  19 {
  20         const unsigned char *data, *top;
  21         unsigned char *dst_buf, *out, cmd;
  22         unsigned long size;
  23         int i;
  24
  25         /* the smallest delta size possible is 6 bytes */
  26         if (delta_size < 6)
  27                 return NULL;
  28
  29         data = delta_buf;
  30         top = delta_buf + delta_size;
  31
  32         /* make sure the orig file size matches what we expect */
  33         size = i = 0;
  34         cmd = *data++;
  35         while (cmd) {
  36                 if (cmd & 1)
  37                         size |= *data++ << i;
  38                 i += 8;
  39                 cmd >>= 1;
  40         }
  41         if (size != src_size)
  42                 return NULL;
  43
  44         /* now the result size */
  45         size = i = 0;
  46         cmd = *data++;
  47         while (cmd) {
  48                 if (cmd & 1)
  49                         size |= *data++ << i;
  50                 i += 8;
  51                 cmd >>= 1;
  52         }
  53         dst_buf = malloc(size);
  54         if (!dst_buf)
  55                 return NULL;
  56
  57         out = dst_buf;
  58         while (data < top) {
  59                 cmd = *data++;
  60                 if (cmd & 0x80) {
  61                         unsigned long cp_off = 0, cp_size = 0;
  62                         const unsigned char *buf;
  63                         if (cmd & 0x01) cp_off = *data++;
  64                         if (cmd & 0x02) cp_off |= (*data++ << 8);
  65                         if (cmd & 0x04) cp_off |= (*data++ << 16);
  66                         if (cmd & 0x08) cp_off |= (*data++ << 24);
  67                         if (cmd & 0x10) cp_size = *data++;
  68                         if (cmd & 0x20) cp_size |= (*data++ << 8);
  69                         if (cp_size == 0) cp_size = 0x10000;
  70                         buf = (cmd & 0x40) ? dst_buf : src_buf;
  71                         memcpy(out, buf + cp_off, cp_size);
  72                         out += cp_size;
  73                 } else {
  74                         memcpy(out, data, cmd);
  75                         out += cmd;
  76                         data += cmd;
  77                 }
  78         }
  79
  80         /* sanity check */
  81         if (data != top || out - dst_buf != size) {
  82                 free(dst_buf);
  83                 return NULL;
  84         }
  85
  86         *dst_size = size;
  87         return dst_buf;
  88 }