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.  xdelta can express an edit that copies
  20 * data inside of the destination which originally came from the
  21 * source.  We do not count that in the following routine, so we are
  22 * undercounting the source material that remains in the final output
  23 * that way.
  24 */
  25int count_delta(void *delta_buf, unsigned long delta_size,
  26                unsigned long *src_copied, unsigned long *literal_added)
  27{
  28        unsigned long copied_from_source, added_literal;
  29        const unsigned char *data, *top;
  30        unsigned char cmd;
  31        unsigned long src_size, dst_size, out;
  32
  33        if (delta_size < DELTA_SIZE_MIN)
  34                return -1;
  35
  36        data = delta_buf;
  37        top = delta_buf + delta_size;
  38
  39        src_size = get_delta_hdr_size(&data);
  40        dst_size = get_delta_hdr_size(&data);
  41
  42        added_literal = copied_from_source = out = 0;
  43        while (data < top) {
  44                cmd = *data++;
  45                if (cmd & 0x80) {
  46                        unsigned long cp_off = 0, cp_size = 0;
  47                        if (cmd & 0x01) cp_off = *data++;
  48                        if (cmd & 0x02) cp_off |= (*data++ << 8);
  49                        if (cmd & 0x04) cp_off |= (*data++ << 16);
  50                        if (cmd & 0x08) cp_off |= (*data++ << 24);
  51                        if (cmd & 0x10) cp_size = *data++;
  52                        if (cmd & 0x20) cp_size |= (*data++ << 8);
  53                        if (cp_size == 0) cp_size = 0x10000;
  54
  55                        if (cmd & 0x40)
  56                                /* copy from dst */
  57                                ;
  58                        else
  59                                copied_from_source += cp_size;
  60                        out += cp_size;
  61                } else {
  62                        /* write literal into dst */
  63                        added_literal += cmd;
  64                        out += cmd;
  65                        data += cmd;
  66                }
  67        }
  68
  69        /* sanity check */
  70        if (data != top || out != dst_size)
  71                return -1;
  72
  73        /* delete size is what was _not_ copied from source.
  74         * edit size is that and literal additions.
  75         */
  76        *src_copied = copied_from_source;
  77        *literal_added = added_literal;
  78        return 0;
  79}