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idtag.c

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00001 /*
00002   Copyright (c) 2005, The Musepack Development Team
00003   All rights reserved.
00004 
00005   Redistribution and use in source and binary forms, with or without
00006   modification, are permitted provided that the following conditions are
00007   met:
00008 
00009   * Redistributions of source code must retain the above copyright
00010   notice, this list of conditions and the following disclaimer.
00011 
00012   * Redistributions in binary form must reproduce the above
00013   copyright notice, this list of conditions and the following
00014   disclaimer in the documentation and/or other materials provided
00015   with the distribution.
00016 
00017   * Neither the name of the The Musepack Development Team nor the
00018   names of its contributors may be used to endorse or promote
00019   products derived from this software without specific prior
00020   written permission.
00021 
00022   THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
00023   "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
00024   LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
00025   A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
00026   OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
00027   SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
00028   LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
00029   DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
00030   THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
00031   (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
00032   OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
00033 */
00034 
00038 
00039 #include <mpcdec/mpcdec.h>
00040 #include <mpcdec/internal.h>
00041 
00042 mpc_int32_t
00043 JumpID3v2 (mpc_reader* r) {
00044     unsigned char  tmp [10];
00045     mpc_uint32_t   Unsynchronisation;   // ID3v2.4-flag
00046     mpc_uint32_t   ExtHeaderPresent;    // ID3v2.4-flag
00047     mpc_uint32_t   ExperimentalFlag;    // ID3v2.4-flag
00048     mpc_uint32_t   FooterPresent;       // ID3v2.4-flag
00049     mpc_int32_t    ret;
00050 
00051     // seek to first byte of mpc data
00052     if (!r->seek (r->data, 0)) {
00053         return 0;  
00054     }
00055     
00056     r->read(r->data, tmp, sizeof(tmp));
00057 
00058     // check id3-tag
00059     if ( 0 != memcmp ( tmp, "ID3", 3) )
00060         return 0;
00061 
00062     // read flags
00063     Unsynchronisation = tmp[5] & 0x80;
00064     ExtHeaderPresent  = tmp[5] & 0x40;
00065     ExperimentalFlag  = tmp[5] & 0x20;
00066     FooterPresent     = tmp[5] & 0x10;
00067 
00068     if ( tmp[5] & 0x0F )
00069         return -1;              // not (yet???) allowed
00070     if ( (tmp[6] | tmp[7] | tmp[8] | tmp[9]) & 0x80 )
00071         return -1;              // not allowed
00072 
00073     // read HeaderSize (syncsave: 4 * $0xxxxxxx = 28 significant bits)
00074     ret  = tmp[6] << 21;
00075     ret += tmp[7] << 14;
00076     ret += tmp[8] <<  7;
00077     ret += tmp[9]      ;
00078     ret += 10;
00079     if ( FooterPresent )
00080         ret += 10;
00081 
00082     return ret;
00083 }

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