vorbis_find_page()

static uint32 fl::third_party::vorbis::vorbis_find_page ( stb_vorbis * f, uint32 * end, uint32 * last )

static

Definition at line 4319 of file stb_vorbis.cpp.hpp.

{
   for(;;) {
      int32_t n;
      if (f->eof) return 0;
      n = get8(f);
      if (n == 0x4f) { // page header candidate
         uint32_t retry_loc = stb_vorbis_get_file_offset(f);
         int32_t i;
         // check if we're off the end of a file_section stream
         if (retry_loc - 25 > f->stream_len)
            return 0;
         // check the rest of the header
         for (i=1; i < 4; ++i)
            if (get8(f) != ogg_page_header[i])
               break;
         if (f->eof) return 0;
         if (i == 4) {
            uint8 header[27];
            uint32 i, crc, goal, len;
            for (i=0; i < 4; ++i)
               header[i] = ogg_page_header[i];
            for (; i < 27; ++i)
               header[i] = get8(f);
            if (f->eof) return 0;
            if (header[4] != 0) goto invalid;
            goal = header[22] + (header[23] << 8) + ((uint32)header[24]<<16) + ((uint32)header[25]<<24);
            for (i=22; i < 26; ++i)
               header[i] = 0;
            crc = 0;
            for (i=0; i < 27; ++i)
               crc = crc32_update(crc, header[i]);
            len = 0;
            for (i=0; i < header[26]; ++i) {
               int32_t s = get8(f);
               crc = crc32_update(crc, s);
               len += s;
            }
            if (len && f->eof) return 0;
            for (i=0; i < len; ++i)
               crc = crc32_update(crc, get8(f));
            // finished parsing probable page
            if (crc == goal) {
               // we could now check that it's either got the last
               // page flag set, OR it's followed by the capture
               // pattern, but I guess TECHNICALLY you could have
               // a file with garbage between each ogg page and recover
               // from it automatically? So even though that paranoia
               // might decrease the chance of an invalid decode by
               // another 2^32, not worth it since it would hose those
               // invalid-but-useful files?
               if (end)
                  *end = stb_vorbis_get_file_offset(f);
               if (last) {
                  if (header[5] & 0x04)
                     *last = 1;
                  else
                     *last = 0;
               }
               set_file_offset(f, retry_loc-1);
               return 1;
            }
         }
        invalid:
         // not a valid page, so rewind and look for next one
         set_file_offset(f, retry_loc);
      }
   }
}

References crc32_update(), fl::end(), FL_NOEXCEPT, get8(), ogg_page_header, set_file_offset(), and stb_vorbis_get_file_offset().

Referenced by go_to_page_before(), seek_to_sample_coarse(), and stb_vorbis_stream_length_in_samples().

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