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>.
9 #include "count-delta.h"
11 static unsigned long get_hdr_size(const unsigned char **datap)
13 const unsigned char *data = *datap;
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. Number of
33 * bytes that are _not_ copied from the source is deletion, and number
34 * of inserted literal bytes are addition, so sum of them is what we
35 * return. xdelta can express an edit that copies data inside of the
36 * destination which originally came from the source. We do not count
37 * that in the following routine, so we are undercounting the source
38 * material that remains in the final output that way.
40 unsigned long count_delta(void *delta_buf, unsigned long delta_size)
42 unsigned long copied_from_source, added_literal;
43 const unsigned char *data, *top;
45 unsigned long src_size, dst_size, out;
47 /* the smallest delta size possible is 6 bytes */
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;
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;
74 copied_from_source += cp_size;
77 /* write literal into dst */
85 if (data != top || out != dst_size)
88 /* delete size is what was _not_ copied from source.
89 * edit size is that and literal additions.
91 if (src_size + added_literal < copied_from_source)
92 /* we ended up overcounting and underflowed */
94 return (src_size - copied_from_source) + added_literal;