Merge master.kernel.org:/pub/scm/gitk/gitk
[git/git.git] / 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. 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 */
25 int 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 }