apps/codecs/libmusepack/idtag.c

   1 /*
   2   Copyright (c) 2005, The Musepack Development Team
   3   All rights reserved.
   4
   5   Redistribution and use in source and binary forms, with or without
   6   modification, are permitted provided that the following conditions are
   7   met:
   8
   9   * Redistributions of source code must retain the above copyright
  10   notice, this list of conditions and the following disclaimer.
  11
  12   * Redistributions in binary form must reproduce the above
  13   copyright notice, this list of conditions and the following
  14   disclaimer in the documentation and/or other materials provided
  15   with the distribution.
  16
  17   * Neither the name of the The Musepack Development Team nor the
  18   names of its contributors may be used to endorse or promote
  19   products derived from this software without specific prior
  20   written permission.
  21
  22   THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
  23   "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
  24   LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
  25   A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
  26   OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
  27   SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
  28   LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
  29   DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
  30   THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
  31   (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
  32   OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  33 */
  34
  35 /// \file idtag.c
  36 /// Rudimentary id3tag handling routines, just enough to skip id3v2 tags,
  37 /// if present.
  38
  39 #include "musepack.h"
  40 #include "internal.h"
  41
  42 mpc_int32_t
  43 JumpID3v2 (mpc_reader* r) {
  44     unsigned char  tmp [10];
  45     mpc_uint32_t   Unsynchronisation;   // ID3v2.4-flag
  46     mpc_uint32_t   ExtHeaderPresent;    // ID3v2.4-flag
  47     mpc_uint32_t   ExperimentalFlag;    // ID3v2.4-flag
  48     mpc_uint32_t   FooterPresent;       // ID3v2.4-flag
  49     mpc_int32_t    ret;
  50
  51     // seek to first byte of mpc data
  52     if (!r->seek (r->data, 0)) {
  53         return 0;
  54     }
  55
  56     r->read(r->data, tmp, sizeof(tmp));
  57
  58     // check id3-tag
  59     if ( 0 != memcmp ( tmp, "ID3", 3) )
  60         return 0;
  61
  62     // read flags
  63     Unsynchronisation = tmp[5] & 0x80;
  64     ExtHeaderPresent  = tmp[5] & 0x40;
  65     ExperimentalFlag  = tmp[5] & 0x20;
  66     FooterPresent     = tmp[5] & 0x10;
  67
  68     if ( tmp[5] & 0x0F )
  69         return -1;              // not (yet???) allowed
  70     if ( (tmp[6] | tmp[7] | tmp[8] | tmp[9]) & 0x80 )
  71         return -1;              // not allowed
  72
  73     // read HeaderSize (syncsave: 4 * $0xxxxxxx = 28 significant bits)
  74     ret  = tmp[6] << 21;
  75     ret += tmp[7] << 14;
  76     ret += tmp[8] <<  7;
  77     ret += tmp[9]      ;
  78     ret += 10;
  79     if ( FooterPresent )
  80         ret += 10;
  81
  82     return ret;
  83 }