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/*
* Copyright (C) 2005 Junio C Hamano
* The delta-parsing part is almost straight copy of patch-delta.c
* which is (C) 2005 Nicolas Pitre <nico@cam.org>.
*/
#include <stdlib.h>
#include <string.h>
#include <limits.h>
#include "count-delta.h"
static unsigned long get_hdr_size(const unsigned char **datap)
{
const unsigned char *data = *datap;
unsigned long size;
unsigned char cmd;
int i;
size = i = 0;
cmd = *data++;
while (cmd) {
if (cmd & 1)
size |= *data++ << i;
i += 8;
cmd >>= 1;
}
*datap = data;
return size;
}
/*
* NOTE. We do not _interpret_ delta fully. As an approximation, we
* just count the number of bytes that are copied from the source, and
* the number of literal data bytes that are inserted. Number of
* bytes that are _not_ copied from the source is deletion, and number
* of inserted literal bytes are addition, so sum of them is what we
* return. xdelta can express an edit that copies data inside of the
* destination which originally came from the source. We do not count
* that in the following routine, so we are undercounting the source
* material that remains in the final output that way.
*/
unsigned long count_delta(void *delta_buf, unsigned long delta_size)
{
unsigned long copied_from_source, added_literal;
const unsigned char *data, *top;
unsigned char cmd;
unsigned long src_size, dst_size, out;
/* the smallest delta size possible is 6 bytes */
if (delta_size < 6)
return UINT_MAX;
data = delta_buf;
top = delta_buf + delta_size;
src_size = get_hdr_size(&data);
dst_size = get_hdr_size(&data);
added_literal = copied_from_source = out = 0;
while (data < top) {
cmd = *data++;
if (cmd & 0x80) {
unsigned long cp_off = 0, cp_size = 0;
if (cmd & 0x01) cp_off = *data++;
if (cmd & 0x02) cp_off |= (*data++ << 8);
if (cmd & 0x04) cp_off |= (*data++ << 16);
if (cmd & 0x08) cp_off |= (*data++ << 24);
if (cmd & 0x10) cp_size = *data++;
if (cmd & 0x20) cp_size |= (*data++ << 8);
if (cp_size == 0) cp_size = 0x10000;
if (cmd & 0x40)
/* copy from dst */
;
else
copied_from_source += cp_size;
out += cp_size;
} else {
/* write literal into dst */
added_literal += cmd;
out += cmd;
data += cmd;
}
}
/* sanity check */
if (data != top || out != dst_size)
return UINT_MAX;
/* delete size is what was _not_ copied from source.
* edit size is that and literal additions.
*/
if (src_size + added_literal < copied_from_source)
/* we ended up overcounting and underflowed */
return 0;
return (src_size - copied_from_source) + added_literal;
}
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