Andrew's git - gitweb.git/blob

   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 "cache.h"
   7#include "delta.h"
   8#include "count-delta.h"
   9#include <stdlib.h>
  10#include <string.h>
  11#include <limits.h>
  12
  13struct span {
  14        struct span *next;
  15        unsigned long ofs;
  16        unsigned long end;
  17};
  18
  19static void touch_range(struct span **span,
  20                        unsigned long ofs, unsigned long end)
  21{
  22        struct span *e = *span;
  23        struct span *p = NULL;
  24
  25        while (e && e->ofs <= ofs) {
  26                again:
  27                if (ofs < e->end) {
  28                        while (e->end < end) {
  29                                if (e->next) {
  30                                        e->end = e->next->ofs;
  31                                        e = e->next;
  32                                }
  33                                else {
  34                                        e->end = end;
  35                                        return;
  36                                }
  37                        }
  38                        return;
  39                }
  40                p = e;
  41                e = e->next;
  42        }
  43        if (e && e->ofs <= end) {
  44                e->ofs = ofs;
  45                goto again;
  46        }
  47        else {
  48                e = xmalloc(sizeof(*e));
  49                e->ofs = ofs;
  50                e->end = end;
  51                if (p) {
  52                        e->next = p->next;
  53                        p->next = e;
  54                }
  55                else {
  56                        e->next = *span;
  57                        *span = e;
  58                }
  59        }
  60}
  61
  62static unsigned long count_range(struct span *s)
  63{
  64        struct span *t;
  65        unsigned long sz = 0;
  66        while (s) {
  67                t = s;
  68                sz += s->end - s->ofs;
  69                s = s->next;
  70                free(t);
  71        }
  72        return sz;
  73}
  74
  75/*
  76 * NOTE.  We do not _interpret_ delta fully.  As an approximation, we
  77 * just count the number of bytes that are copied from the source, and
  78 * the number of literal data bytes that are inserted.
  79 *
  80 * Number of bytes that are _not_ copied from the source is deletion,
  81 * and number of inserted literal bytes are addition, so sum of them
  82 * is the extent of damage.
  83 */
  84int count_delta(void *delta_buf, unsigned long delta_size,
  85                unsigned long *src_copied, unsigned long *literal_added)
  86{
  87        unsigned long added_literal;
  88        const unsigned char *data, *top;
  89        unsigned char cmd;
  90        unsigned long src_size, dst_size, out;
  91        struct span *span = NULL;
  92
  93        if (delta_size < DELTA_SIZE_MIN)
  94                return -1;
  95
  96        data = delta_buf;
  97        top = delta_buf + delta_size;
  98
  99        src_size = get_delta_hdr_size(&data);
 100        dst_size = get_delta_hdr_size(&data);
 101
 102        added_literal = out = 0;
 103        while (data < top) {
 104                cmd = *data++;
 105                if (cmd & 0x80) {
 106                        unsigned long cp_off = 0, cp_size = 0;
 107                        if (cmd & 0x01) cp_off = *data++;
 108                        if (cmd & 0x02) cp_off |= (*data++ << 8);
 109                        if (cmd & 0x04) cp_off |= (*data++ << 16);
 110                        if (cmd & 0x08) cp_off |= (*data++ << 24);
 111                        if (cmd & 0x10) cp_size = *data++;
 112                        if (cmd & 0x20) cp_size |= (*data++ << 8);
 113                        if (cmd & 0x40) cp_size |= (*data++ << 16);
 114                        if (cp_size == 0) cp_size = 0x10000;
 115
 116                        touch_range(&span, cp_off, cp_off+cp_size);
 117                        out += cp_size;
 118                } else {
 119                        /* write literal into dst */
 120                        added_literal += cmd;
 121                        out += cmd;
 122                        data += cmd;
 123                }
 124        }
 125
 126        *src_copied = count_range(span);
 127
 128        /* sanity check */
 129        if (data != top || out != dst_size)
 130                return -1;
 131
 132        /* delete size is what was _not_ copied from source.
 133         * edit size is that and literal additions.
 134         */
 135        *literal_added = added_literal;
 136        return 0;
 137}