src/minblorb.c

   1 /* minblorb.c: only those portions of the blorb spec needed for cover art
   2
   3    Copyright 2011 Lewis Gentry.
   4
   5    This program is free software: you can redistribute it and/or
   6    modify it under the terms of the GNU General Public License as
   7    published by the Free Software Foundation, either version 3 of the
   8    License, or (at your option) any later version.
   9
  10    This program is distributed in the hope that it will be useful, but
  11    WITHOUT ANY WARRANTY; without even the implied warranty of
  12    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
  13    General Public License for more details.
  14
  15    You should have received a copy of the GNU General Public License
  16    along with this program. If not, see <http://www.gnu.org/licenses/>. */
  17
  18 #include <stdio.h>
  19 #include <string.h>
  20
  21 /* File format reference: <http://www.eblong.com/zarf/blorb/>. */
  22
  23 /* Important offsets: */
  24
  25 #define RESOURCE_INDEX 0x0C /* Beginning of resource index. */
  26 #define RESOURCE_COUNT 0x14 /* Number of resources. */
  27
  28 /* Does this file look like a blorb? */
  29
  30 int verify(FILE *blorb)
  31 {
  32   char signature[12];
  33
  34   rewind(blorb);
  35   return fread(signature, sizeof(char), 12, blorb) == 12
  36     && memcmp(signature + 0, "FORM", 4) == 0
  37     && memcmp(signature + 8, "IFRS", 4) == 0;
  38 }
  39
  40 /* Convert a four-byte word (big-endian) to an integer. */
  41
  42 unsigned int int32_read(unsigned char *word)
  43 {
  44   return word[0] * 16777216 + word[1] * 65536 + word[2] * 256 + word[3];
  45 }
  46
  47 /* As above, but rounded up to an even number per the IFF spec. */
  48
  49 unsigned int int32_padded(unsigned char *word)
  50 {
  51   unsigned int i;
  52
  53   i = int32_read(word);
  54   return i % 2 ? i + 1 : i;
  55 }
  56
  57 /* Does the stream contain a frontispiece chunk? If so, store its
  58    resource number in the provided pointer. */
  59
  60 int fspc(FILE *blorb, unsigned int *resource)
  61 {
  62   unsigned char buffer[8] = { 0, 0, 0, 0, 0, 0, 0, RESOURCE_INDEX };
  63   unsigned char target[4];
  64
  65   rewind(blorb);
  66   while (fseek(blorb, int32_padded(buffer + 4), SEEK_CUR) == 0
  67          && fread(buffer, sizeof(char), 8, blorb) == 8) {
  68     if (memcmp(buffer, "Fspc", 4) == 0
  69         && fread(target, sizeof(char), 4, blorb) == 4) {
  70       *resource = int32_read(target);
  71       return 1;
  72     }
  73   }
  74   return 0;
  75 }
  76
  77 /* Does the picture with this resource number exist? If so, return its
  78    address. */
  79
  80 unsigned int findpict(FILE *blorb, unsigned int id)
  81 {
  82   unsigned char buffer[12];
  83   int resources;
  84
  85   if (fseek(blorb, RESOURCE_COUNT, SEEK_SET) == 0
  86       && fread(buffer, sizeof(char), 4, blorb) == 4) {
  87     resources = int32_read(buffer);
  88     while (resources-- && fread(buffer, sizeof(char), 12, blorb) == 12)
  89       if (memcmp(buffer, "Pict", 4) == 0 && int32_read(buffer + 4) == id)
  90         return int32_read(buffer + 8);
  91   }
  92   return 0;
  93 }
  94
  95 /* How long is the chunk at this offset? (As a useful side effect, the
  96    stream is now positioned at the beginning of the chunk data.) */
  97
  98 unsigned int chunklength(FILE *blorb, unsigned int offset)
  99 {
 100   unsigned char buffer[8];
 101
 102   return fseek(blorb, offset, SEEK_SET) == 0
 103     && fread(buffer, sizeof(char), 8, blorb) == 8
 104     ? int32_read(buffer + 4) : 0;
 105 }