Andrew's git - gitweb.git/blob

   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 */
  21int 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);
  36        dst_size = get_delta_hdr_size(&data);
  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}