count-delta.c

   1 /*
   2  * Copyright (C) 2005 Junio C Hamano
   3  * The delta-parsing part is almost straight copy of patch-delta.c
   4  * which is (C) 2005 Nicolas Pitre <nico@cam.org>.
   5  */
   6 #include <stdlib.h>
   7 #include <string.h>
   8 #include <limits.h>
   9 #include "delta.h"
  10 #include "count-delta.h"
  11
  12 /*
  13  * NOTE.  We do not _interpret_ delta fully.  As an approximation, we
  14  * just count the number of bytes that are copied from the source, and
  15  * the number of literal data bytes that are inserted.
  16  *
  17  * Number of bytes that are _not_ copied from the source is deletion,
  18  * and number of inserted literal bytes are addition, so sum of them
  19  * is the extent of damage.
  20  */
  21 int count_delta(void *delta_buf, unsigned long delta_size,
  22                 unsigned long *src_copied, unsigned long *literal_added)
  23 {
  24         unsigned long copied_from_source, added_literal;
  25         const unsigned char *data, *top;
  26         unsigned char cmd;
  27         unsigned long src_size, dst_size, out;
  28
  29         if (delta_size < DELTA_SIZE_MIN)
  30                 return -1;
  31
  32         data = delta_buf;
  33         top = delta_buf + delta_size;
  34
  35         src_size = get_delta_hdr_size(&data, top);
  36         dst_size = get_delta_hdr_size(&data, top);
  37
  38         added_literal = copied_from_source = out = 0;
  39         while (data < top) {
  40                 cmd = *data++;
  41                 if (cmd & 0x80) {
  42                         unsigned long cp_off = 0, cp_size = 0;
  43                         if (cmd & 0x01) cp_off = *data++;
  44                         if (cmd & 0x02) cp_off |= (*data++ << 8);
  45                         if (cmd & 0x04) cp_off |= (*data++ << 16);
  46                         if (cmd & 0x08) cp_off |= (*data++ << 24);
  47                         if (cmd & 0x10) cp_size = *data++;
  48                         if (cmd & 0x20) cp_size |= (*data++ << 8);
  49                         if (cmd & 0x40) cp_size |= (*data++ << 16);
  50                         if (cp_size == 0) cp_size = 0x10000;
  51
  52                         copied_from_source += cp_size;
  53                         out += cp_size;
  54                 } else {
  55                         /* write literal into dst */
  56                         added_literal += cmd;
  57                         out += cmd;
  58                         data += cmd;
  59                 }
  60         }
  61
  62         /* sanity check */
  63         if (data != top || out != dst_size)
  64                 return -1;
  65
  66         /* delete size is what was _not_ copied from source.
  67          * edit size is that and literal additions.
  68          */
  69         *src_copied = copied_from_source;
  70         *literal_added = added_literal;
  71         return 0;
  72 }