8901034188c4d17be6676dd1fd532a23384cb5cb
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"
11 static unsigned long get_hdr_size(const unsigned char **datap)
12 {
13 const unsigned char *data = *datap;
14 unsigned char cmd = *data++;
15 unsigned long size = cmd & ~0x80;
16 int i = 7;
17 while (cmd & 0x80) {
18 cmd = *data++;
19 size |= (cmd & ~0x80) << i;
20 i += 7;
21 }
22 *datap = data;
23 return size;
24 }
26 /*
27 * NOTE. We do not _interpret_ delta fully. As an approximation, we
28 * just count the number of bytes that are copied from the source, and
29 * the number of literal data bytes that are inserted.
30 *
31 * Number of bytes that are _not_ copied from the source is deletion,
32 * and number of inserted literal bytes are addition, so sum of them
33 * is the extent of damage. xdelta can express an edit that copies
34 * data inside of the destination which originally came from the
35 * source. We do not count that in the following routine, so we are
36 * undercounting the source material that remains in the final output
37 * that way.
38 */
39 int count_delta(void *delta_buf, unsigned long delta_size,
40 unsigned long *src_copied, unsigned long *literal_added)
41 {
42 unsigned long copied_from_source, added_literal;
43 const unsigned char *data, *top;
44 unsigned char cmd;
45 unsigned long src_size, dst_size, out;
47 /* the smallest delta size possible is 4 bytes */
48 if (delta_size < 4)
49 return -1;
51 data = delta_buf;
52 top = delta_buf + delta_size;
54 src_size = get_hdr_size(&data);
55 dst_size = get_hdr_size(&data);
57 added_literal = copied_from_source = out = 0;
58 while (data < top) {
59 cmd = *data++;
60 if (cmd & 0x80) {
61 unsigned long cp_off = 0, cp_size = 0;
62 if (cmd & 0x01) cp_off = *data++;
63 if (cmd & 0x02) cp_off |= (*data++ << 8);
64 if (cmd & 0x04) cp_off |= (*data++ << 16);
65 if (cmd & 0x08) cp_off |= (*data++ << 24);
66 if (cmd & 0x10) cp_size = *data++;
67 if (cmd & 0x20) cp_size |= (*data++ << 8);
68 if (cp_size == 0) cp_size = 0x10000;
70 if (cmd & 0x40)
71 /* copy from dst */
72 ;
73 else
74 copied_from_source += cp_size;
75 out += cp_size;
76 } else {
77 /* write literal into dst */
78 added_literal += cmd;
79 out += cmd;
80 data += cmd;
81 }
82 }
84 /* sanity check */
85 if (data != top || out != dst_size)
86 return -1;
88 /* delete size is what was _not_ copied from source.
89 * edit size is that and literal additions.
90 */
91 *src_copied = copied_from_source;
92 *literal_added = added_literal;
93 return 0;
94 }