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00001 /*
00002     getbits
00003 
00004     copyright ?-2009 by the mpg123 project - free software under the terms of the LGPL 2.1
00005     see COPYING and AUTHORS files in distribution or http://mpg123.org
00006     initially written by Michael Hipp
00007 
00008     All code is in the header to suggest/force inlining of these small often-used functions.
00009     This indeed has some impact on performance.
00010 */
00011 
00012 #ifndef _MPG123_GETBITS_H_
00013 #define _MPG123_GETBITS_H_
00014 
00015 #include "mpg123lib_intern.h"
00016 
00017 #define backbits(fr,nob) ((void)( \
00018   fr->bitindex    -= nob, \
00019   fr->wordpointer += (fr->bitindex>>3), \
00020   fr->bitindex    &= 0x7 ))
00021 
00022 #define getbitoffset(fr) ((-fr->bitindex)&0x7)
00023 #define getbyte(fr)      (*fr->wordpointer++)
00024 
00025 /* There is something wrong with that macro... the function below works also for the layer1 test case. */
00026 #define macro_getbits(fr, nob) ( \
00027   fr->ultmp = fr->wordpointer[0],\
00028   fr->ultmp <<= 8, \
00029   fr->ultmp |= fr->wordpointer[1], \
00030   fr->ultmp <<= 8, \
00031   fr->ultmp |= fr->wordpointer[2], \
00032   fr->ultmp <<= fr->bitindex, \
00033   fr->ultmp &= 0xffffff, \
00034   fr->bitindex += nob, \
00035   fr->ultmp >>= (24-nob), \
00036   fr->wordpointer += (fr->bitindex>>3), \
00037   fr->bitindex &= 7, \
00038   fr->ultmp)
00039 
00040 static unsigned int getbits(mpg123_handle *fr, int number_of_bits)
00041 {
00042   unsigned long rval;
00043 
00044 #ifdef DEBUG_GETBITS
00045 fprintf(stderr,"g%d",number_of_bits);
00046 #endif
00047 
00048 /*  This is actually slow: if(!number_of_bits)
00049     return 0; */
00050 
00051 #if 0
00052    check_buffer_range(number_of_bits+fr->bitindex);
00053 #endif
00054 
00055   {
00056     rval = fr->wordpointer[0];
00057     rval <<= 8;
00058     rval |= fr->wordpointer[1];
00059     rval <<= 8;
00060     rval |= fr->wordpointer[2];
00061 
00062     rval <<= fr->bitindex;
00063     rval &= 0xffffff;
00064 
00065     fr->bitindex += number_of_bits;
00066 
00067     rval >>= (24-number_of_bits);
00068 
00069     fr->wordpointer += (fr->bitindex>>3);
00070     fr->bitindex &= 7;
00071   }
00072 
00073 #ifdef DEBUG_GETBITS
00074 fprintf(stderr,":%lx\n",rval);
00075 #endif
00076 
00077   return rval;
00078 }
00079 
00080 
00081 #define skipbits(fr, nob) fr->ultmp = ( \
00082   fr->ultmp = fr->wordpointer[0], fr->ultmp <<= 8, fr->ultmp |= fr->wordpointer[1], \
00083   fr->ultmp <<= 8, fr->ultmp |= fr->wordpointer[2], fr->ultmp <<= fr->bitindex, \
00084   fr->ultmp &= 0xffffff, fr->bitindex += nob, \
00085   fr->ultmp >>= (24-nob), fr->wordpointer += (fr->bitindex>>3), \
00086   fr->bitindex &= 7 )
00087 
00088 #define getbits_fast(fr, nob) ( \
00089   fr->ultmp = (unsigned char) (fr->wordpointer[0] << fr->bitindex), \
00090   fr->ultmp |= ((unsigned long) fr->wordpointer[1]<<fr->bitindex)>>8, \
00091   fr->ultmp <<= nob, fr->ultmp >>= 8, \
00092   fr->bitindex += nob, fr->wordpointer += (fr->bitindex>>3), \
00093   fr->bitindex &= 7, fr->ultmp )
00094 
00095 #define get1bit(fr) ( \
00096   fr->uctmp = *fr->wordpointer << fr->bitindex, fr->bitindex++, \
00097   fr->wordpointer += (fr->bitindex>>3), fr->bitindex &= 7, fr->uctmp>>7 )
00098 
00099 
00100 #endif
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