liba52/bitstream.h

   1 /*
   2  * bitstream.h
   3  * Copyright (C) 2000-2001 Michel Lespinasse <walken@zoy.org>
   4  * Copyright (C) 1999-2000 Aaron Holtzman <aholtzma@ess.engr.uvic.ca>
   5  *
   6  * This file is part of a52dec, a free ATSC A-52 stream decoder.
   7  * See http://liba52.sourceforge.net/ for updates.
   8  *
   9  * Modified for use with MPlayer, changes contained in liba52_changes.diff.
  10  * detailed CVS changelog at http://www.mplayerhq.hu/cgi-bin/cvsweb.cgi/main/
  11  * $Id$
  12  *
  13  * a52dec is free software; you can redistribute it and/or modify
  14  * it under the terms of the GNU General Public License as published by
  15  * the Free Software Foundation; either version 2 of the License, or
  16  * (at your option) any later version.
  17  *
  18  * a52dec is distributed in the hope that it will be useful,
  19  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  20  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  21  * GNU General Public License for more details.
  22  *
  23  * You should have received a copy of the GNU General Public License
  24  * along with this program; if not, write to the Free Software
  25  * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
  26  */
  27
  28 /* code from ffmpeg/libavcodec */
  29 #if defined(__GNUC__) && (__GNUC__ > 3 || __GNUC_ == 3 && __GNUC_MINOR__ > 0)
  30 #    define always_inline __attribute__((always_inline)) inline
  31 #else
  32 #    define always_inline inline
  33 #endif
  34
  35 #if defined(__sparc__) || defined(hpux)
  36 /*
  37  * the alt bitstream reader performs unaligned memory accesses; that doesn't work
  38  * on sparc/hpux.  For now, disable ALT_BITSTREAM_READER.
  39  */
  40 #undef  ALT_BITSTREAM_READER
  41 #else
  42 // alternative (faster) bitstram reader (reades upto 3 bytes over the end of the input)
  43 #define ALT_BITSTREAM_READER
  44
  45 /* used to avoid missaligned exceptions on some archs (alpha, ...) */
  46 #if defined (ARCH_X86) || defined(ARCH_ARMV4L)
  47 #    define unaligned32(a) (*(uint32_t*)(a))
  48 #else
  49 #    ifdef __GNUC__
  50 static always_inline uint32_t unaligned32(const void *v) {
  51     struct Unaligned {
  52         uint32_t i;
  53     } __attribute__((packed));
  54
  55     return ((const struct Unaligned *) v)->i;
  56 }
  57 #    elif defined(__DECC)
  58 static inline uint32_t unaligned32(const void *v) {
  59     return *(const __unaligned uint32_t *) v;
  60 }
  61 #    else
  62 static inline uint32_t unaligned32(const void *v) {
  63     return *(const uint32_t *) v;
  64 }
  65 #    endif
  66 #endif //!ARCH_X86
  67
  68 #endif
  69
  70 /* (stolen from the kernel) */
  71 #ifdef WORDS_BIGENDIAN
  72
  73 #       define swab32(x) (x)
  74
  75 #else
  76
  77 #       if defined (__i386__)
  78
  79 #       define swab32(x) __i386_swab32(x)
  80         static always_inline const uint32_t __i386_swab32(uint32_t x)
  81         {
  82                 __asm__("bswap %0" : "=r" (x) : "0" (x));
  83                 return x;
  84         }
  85
  86 #       else
  87
  88 #       define swab32(x) __generic_swab32(x)
  89         static always_inline const uint32_t __generic_swab32(uint32_t x)
  90         {
  91                 return ((((uint8_t*)&x)[0] << 24) | (((uint8_t*)&x)[1] << 16) |
  92                  (((uint8_t*)&x)[2] << 8)  | (((uint8_t*)&x)[3]));
  93         }
  94 #       endif
  95 #endif
  96
  97 #ifdef ALT_BITSTREAM_READER
  98 extern uint32_t *buffer_start;
  99 extern int indx;
 100 #else
 101 extern uint32_t bits_left;
 102 extern uint32_t current_word;
 103 #endif
 104
 105 void bitstream_set_ptr (uint8_t * buf);
 106 uint32_t bitstream_get_bh(uint32_t num_bits);
 107 int32_t bitstream_get_bh_2(uint32_t num_bits);
 108
 109
 110 static inline uint32_t
 111 bitstream_get(uint32_t num_bits) // note num_bits is practically a constant due to inlineing
 112 {
 113 #ifdef ALT_BITSTREAM_READER
 114     uint32_t result= swab32( unaligned32(((uint8_t *)buffer_start)+(indx>>3)) );
 115
 116     result<<= (indx&0x07);
 117     result>>= 32 - num_bits;
 118     indx+= num_bits;
 119
 120     return result;
 121 #else
 122     uint32_t result;
 123
 124     if(num_bits < bits_left) {
 125         result = (current_word << (32 - bits_left)) >> (32 - num_bits);
 126         bits_left -= num_bits;
 127         return result;
 128     }
 129
 130     return bitstream_get_bh(num_bits);
 131 #endif
 132 }
 133
 134 static inline void bitstream_skip(int num_bits)
 135 {
 136 #ifdef ALT_BITSTREAM_READER
 137         indx+= num_bits;
 138 #else
 139         bitstream_get(num_bits);
 140 #endif
 141 }
 142
 143 static inline int32_t
 144 bitstream_get_2(uint32_t num_bits)
 145 {
 146 #ifdef ALT_BITSTREAM_READER
 147     int32_t result= swab32( unaligned32(((uint8_t *)buffer_start)+(indx>>3)) );
 148
 149     result<<= (indx&0x07);
 150     result>>= 32 - num_bits;
 151     indx+= num_bits;
 152
 153     return result;
 154 #else
 155     int32_t result;
 156
 157     if(num_bits < bits_left) {
 158         result = (((int32_t)current_word) << (32 - bits_left)) >> (32 - num_bits);
 159         bits_left -= num_bits;
 160         return result;
 161     }
 162
 163     return bitstream_get_bh_2(num_bits);
 164 #endif
 165 }