mirror of
https://github.com/git/git.git
synced 2024-11-24 18:33:43 +08:00
69a2d426f0
Since the delta data format is not tied to any actual git object anymore, now is the time to add a small improvement to the delta data header as it is been done for packed object header. This patch allows for reducing the delta header of about 2 bytes and makes for simpler code. Signed-off-by: Nicolas Pitre <nico@cam.org> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
95 lines
2.5 KiB
C
95 lines
2.5 KiB
C
/*
|
|
* 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 char cmd = *data++;
|
|
unsigned long size = cmd & ~0x80;
|
|
int i = 7;
|
|
while (cmd & 0x80) {
|
|
cmd = *data++;
|
|
size |= (cmd & ~0x80) << i;
|
|
i += 7;
|
|
}
|
|
*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 the extent of damage. 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.
|
|
*/
|
|
int count_delta(void *delta_buf, unsigned long delta_size,
|
|
unsigned long *src_copied, unsigned long *literal_added)
|
|
{
|
|
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 4 bytes */
|
|
if (delta_size < 4)
|
|
return -1;
|
|
|
|
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 -1;
|
|
|
|
/* delete size is what was _not_ copied from source.
|
|
* edit size is that and literal additions.
|
|
*/
|
|
*src_copied = copied_from_source;
|
|
*literal_added = added_literal;
|
|
return 0;
|
|
}
|