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 "cache.h"
   7 #include "delta.h"
   8 #include "count-delta.h"
   9 #include <stdlib.h>
  10 #include <string.h>
  11 #include <limits.h>
  12
  13 struct span {
  14         struct span *next;
  15         unsigned long ofs;
  16         unsigned long end;
  17 };
  18
  19 static 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 && e->next->ofs <= end) {
  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
  62 static 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  */
  84 int 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 }