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