Do a cross-project merge of Paul Mackerras' gitk visualizer
[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 "count-delta.h"
10
11 static unsigned long get_hdr_size(const unsigned char **datap)
12 {
13 const unsigned char *data = *datap;
14 unsigned long size;
15 unsigned char cmd;
16 int i;
17 size = i = 0;
18 cmd = *data++;
19 while (cmd) {
20 if (cmd & 1)
21 size |= *data++ << i;
22 i += 8;
23 cmd >>= 1;
24 }
25 *datap = data;
26 return size;
27 }
28
29 /*
30 * NOTE. We do not _interpret_ delta fully. As an approximation, we
31 * just count the number of bytes that are copied from the source, and
32 * the number of literal data bytes that are inserted.
33 *
34 * Number of bytes that are _not_ copied from the source is deletion,
35 * and number of inserted literal bytes are addition, so sum of them
36 * is the extent of damage. xdelta can express an edit that copies
37 * data inside of the destination which originally came from the
38 * source. We do not count that in the following routine, so we are
39 * undercounting the source material that remains in the final output
40 * that way.
41 */
42 int count_delta(void *delta_buf, unsigned long delta_size,
43 unsigned long *src_copied, unsigned long *literal_added)
44 {
45 unsigned long copied_from_source, added_literal;
46 const unsigned char *data, *top;
47 unsigned char cmd;
48 unsigned long src_size, dst_size, out;
49
50 /* the smallest delta size possible is 6 bytes */
51 if (delta_size < 6)
52 return -1;
53
54 data = delta_buf;
55 top = delta_buf + delta_size;
56
57 src_size = get_hdr_size(&data);
58 dst_size = get_hdr_size(&data);
59
60 added_literal = copied_from_source = out = 0;
61 while (data < top) {
62 cmd = *data++;
63 if (cmd & 0x80) {
64 unsigned long cp_off = 0, cp_size = 0;
65 if (cmd & 0x01) cp_off = *data++;
66 if (cmd & 0x02) cp_off |= (*data++ << 8);
67 if (cmd & 0x04) cp_off |= (*data++ << 16);
68 if (cmd & 0x08) cp_off |= (*data++ << 24);
69 if (cmd & 0x10) cp_size = *data++;
70 if (cmd & 0x20) cp_size |= (*data++ << 8);
71 if (cp_size == 0) cp_size = 0x10000;
72
73 if (cmd & 0x40)
74 /* copy from dst */
75 ;
76 else
77 copied_from_source += cp_size;
78 out += cp_size;
79 } else {
80 /* write literal into dst */
81 added_literal += cmd;
82 out += cmd;
83 data += cmd;
84 }
85 }
86
87 /* sanity check */
88 if (data != top || out != dst_size)
89 return -1;
90
91 /* delete size is what was _not_ copied from source.
92 * edit size is that and literal additions.
93 */
94 *src_copied = copied_from_source;
95 *literal_added = added_literal;
96 return 0;
97 }