projects / thirdparty / git.git / blame
| Commit | Line | Data |
|---|---|---|
| 85976974 JH |
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> | |
| 85976974 JH |
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. 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. | |
| 39 | */ | |
| 40 | unsigned long count_delta(void *delta_buf, unsigned long delta_size) | |
| 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; | |
| 46 | ||
| 47 | /* the smallest delta size possible is 6 bytes */ | |
| 48 | if (delta_size < 6) | |
| 49 | return UINT_MAX; | |
| 50 | ||
| 51 | data = delta_buf; | |
| 52 | top = delta_buf + delta_size; | |
| 53 | ||
| 54 | src_size = get_hdr_size(&data); | |
| 55 | dst_size = get_hdr_size(&data); | |
| 56 | ||
| 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; | |
| 69 | ||
| 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 | } | |
| 83 | ||
| 84 | /* sanity check */ | |
| 85 | if (data != top || out != dst_size) | |
| 86 | return UINT_MAX; | |
| 87 | ||
| 88 | /* delete size is what was _not_ copied from source. | |
| 89 | * edit size is that and literal additions. | |
| 90 | */ | |
| 8b7d510f JH |
91 | if (src_size + added_literal < copied_from_source) |
| 92 | /* we ended up overcounting and underflowed */ | |
| 93 | return 0; | |
| 85976974 JH |
94 | return (src_size - copied_from_source) + added_literal; |
| 95 | } |