104 lines
2.8 KiB
C
104 lines
2.8 KiB
C
/*
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getbits
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copyright ?-2009 by the mpg123 project - free software under the terms of the LGPL 2.1
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see COPYING and AUTHORS files in distribution or http://mpg123.org
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initially written by Michael Hipp
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All code is in the header to suggest/force inlining of these small often-used functions.
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This indeed has some impact on performance.
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*/
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#ifndef _MPG123_GETBITS_H_
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#define _MPG123_GETBITS_H_
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#include "mpg123lib_intern.h"
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#include "debug.h"
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#define backbits(fr,nob) ((void)( \
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fr->bits_avail += nob, \
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fr->bitindex -= nob, \
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fr->wordpointer += (fr->bitindex>>3), \
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fr->bitindex &= 0x7 ))
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#define getbitoffset(fr) ((-fr->bitindex)&0x7)
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/* Precomputing the bytes to be read is error-prone, and some over-read
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is even expected for Huffman. Just play safe and return zeros in case
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of overflow. This assumes you made bitindex zero already! */
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#define getbyte(fr) ( (fr)->bits_avail-=8, (fr)->bits_avail >= 0 \
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? *((fr)->wordpointer++) \
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: 0 )
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static unsigned int getbits(mpg123_handle *fr, int number_of_bits)
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{
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unsigned long rval;
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#ifdef DEBUG_GETBITS
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fprintf(stderr,"g%d",number_of_bits);
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#endif
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fr->bits_avail -= number_of_bits;
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/* Safety catch until we got the nasty code fully figured out. */
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/* No, that catch stays here, even if we think we got it figured out! */
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if(fr->bits_avail < 0)
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{
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if(NOQUIET)
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error2( "Tried to read %i bits with %li available."
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, number_of_bits, fr->bits_avail );
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return 0;
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}
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/* This is actually slow: if(!number_of_bits)
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return 0; */
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#if 0
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check_buffer_range(number_of_bits+fr->bitindex);
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#endif
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{
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rval = fr->wordpointer[0];
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rval <<= 8;
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rval |= fr->wordpointer[1];
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rval <<= 8;
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rval |= fr->wordpointer[2];
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rval <<= fr->bitindex;
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rval &= 0xffffff;
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fr->bitindex += number_of_bits;
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rval >>= (24-number_of_bits);
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fr->wordpointer += (fr->bitindex>>3);
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fr->bitindex &= 7;
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}
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#ifdef DEBUG_GETBITS
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fprintf(stderr,":%lx\n",rval);
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#endif
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return rval;
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}
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#define skipbits(fr, nob) fr->ultmp = ( \
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fr->ultmp = fr->wordpointer[0], fr->ultmp <<= 8, fr->ultmp |= fr->wordpointer[1], \
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fr->ultmp <<= 8, fr->ultmp |= fr->wordpointer[2], fr->ultmp <<= fr->bitindex, \
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fr->ultmp &= 0xffffff, fr->bitindex += nob, fr->bits_avail -= nob, \
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fr->ultmp >>= (24-nob), fr->wordpointer += (fr->bitindex>>3), \
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fr->bitindex &= 7 )
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#define getbits_fast(fr, nob) ( \
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fr->ultmp = (unsigned char) (fr->wordpointer[0] << fr->bitindex), \
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fr->ultmp |= ((unsigned long) fr->wordpointer[1]<<fr->bitindex)>>8, \
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fr->ultmp <<= nob, fr->ultmp >>= 8, \
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fr->bitindex += nob, fr->bits_avail -= nob, \
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fr->wordpointer += (fr->bitindex>>3), \
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fr->bitindex &= 7, fr->ultmp )
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#define get1bit(fr) ( \
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fr->uctmp = *fr->wordpointer << fr->bitindex, \
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++fr->bitindex, --fr->bits_avail, \
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fr->wordpointer += (fr->bitindex>>3), fr->bitindex &= 7, fr->uctmp>>7 )
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#endif
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