third_party/libwebp/utils/bit_reader_inl.h

   1 // Copyright 2014 Google Inc. All Rights Reserved.
   2 //
   3 // Use of this source code is governed by a BSD-style license
   4 // that can be found in the COPYING file in the root of the source
   5 // tree. An additional intellectual property rights grant can be found
   6 // in the file PATENTS. All contributing project authors may
   7 // be found in the AUTHORS file in the root of the source tree.
   8 // -----------------------------------------------------------------------------
   9 //
  10 // Specific inlined methods for boolean decoder [VP8GetBit() ...]
  11 // This file should be included by the .c sources that actually need to call
  12 // these methods.
  13 //
  14 // Author: Skal (pascal.massimino@gmail.com)
  15
  16 #ifndef WEBP_UTILS_BIT_READER_INL_H_
  17 #define WEBP_UTILS_BIT_READER_INL_H_
  18
  19 #ifdef HAVE_CONFIG_H
  20 #include "../webp/config.h"
  21 #endif
  22
  23 #ifdef WEBP_FORCE_ALIGNED
  24 #include <string.h>  // memcpy
  25 #endif
  26
  27 #include "../dsp/dsp.h"
  28 #include "./bit_reader.h"
  29 #include "./endian_inl.h"
  30
  31 #ifdef __cplusplus
  32 extern "C" {
  33 #endif
  34
  35 //------------------------------------------------------------------------------
  36 // Derived type lbit_t = natural type for memory I/O
  37
  38 #if   (BITS > 32)
  39 typedef uint64_t lbit_t;
  40 #elif (BITS > 16)
  41 typedef uint32_t lbit_t;
  42 #elif (BITS >  8)
  43 typedef uint16_t lbit_t;
  44 #else
  45 typedef uint8_t lbit_t;
  46 #endif
  47
  48 extern const uint8_t kVP8Log2Range[128];
  49 extern const range_t kVP8NewRange[128];
  50
  51 // special case for the tail byte-reading
  52 void VP8LoadFinalBytes(VP8BitReader* const br);
  53
  54 //------------------------------------------------------------------------------
  55 // Inlined critical functions
  56
  57 // makes sure br->value_ has at least BITS bits worth of data
  58 static WEBP_INLINE void VP8LoadNewBytes(VP8BitReader* const br) {
  59   assert(br != NULL && br->buf_ != NULL);
  60   // Read 'BITS' bits at a time if possible.
  61   if (br->buf_ + sizeof(lbit_t) <= br->buf_end_) {
  62     // convert memory type to register type (with some zero'ing!)
  63     bit_t bits;
  64 #if defined(WEBP_FORCE_ALIGNED)
  65     lbit_t in_bits;
  66     memcpy(&in_bits, br->buf_, sizeof(in_bits));
  67 #elif defined(WEBP_USE_MIPS32)
  68     // This is needed because of un-aligned read.
  69     lbit_t in_bits;
  70     lbit_t* p_buf_ = (lbit_t*)br->buf_;
  71     __asm__ volatile(
  72       ".set   push                             \n\t"
  73       ".set   at                               \n\t"
  74       ".set   macro                            \n\t"
  75       "ulw    %[in_bits], 0(%[p_buf_])         \n\t"
  76       ".set   pop                              \n\t"
  77       : [in_bits]"=r"(in_bits)
  78       : [p_buf_]"r"(p_buf_)
  79       : "memory", "at"
  80     );
  81 #else
  82     const lbit_t in_bits = *(const lbit_t*)br->buf_;
  83 #endif
  84     br->buf_ += BITS >> 3;
  85 #if !defined(WORDS_BIGENDIAN)
  86 #if (BITS > 32)
  87     bits = BSwap64(in_bits);
  88     bits >>= 64 - BITS;
  89 #elif (BITS >= 24)
  90     bits = BSwap32(in_bits);
  91     bits >>= (32 - BITS);
  92 #elif (BITS == 16)
  93     bits = BSwap16(in_bits);
  94 #else   // BITS == 8
  95     bits = (bit_t)in_bits;
  96 #endif  // BITS > 32
  97 #else    // WORDS_BIGENDIAN
  98     bits = (bit_t)in_bits;
  99     if (BITS != 8 * sizeof(bit_t)) bits >>= (8 * sizeof(bit_t) - BITS);
 100 #endif
 101     br->value_ = bits | (br->value_ << BITS);
 102     br->bits_ += BITS;
 103   } else {
 104     VP8LoadFinalBytes(br);    // no need to be inlined
 105   }
 106 }
 107
 108 // Read a bit with proba 'prob'. Speed-critical function!
 109 static WEBP_INLINE int VP8GetBit(VP8BitReader* const br, int prob) {
 110   // Don't move this declaration! It makes a big speed difference to store
 111   // 'range' *before* calling VP8LoadNewBytes(), even if this function doesn't
 112   // alter br->range_ value.
 113   range_t range = br->range_;
 114   if (br->bits_ < 0) {
 115     VP8LoadNewBytes(br);
 116   }
 117   {
 118     const int pos = br->bits_;
 119     const range_t split = (range * prob) >> 8;
 120     const range_t value = (range_t)(br->value_ >> pos);
 121 #if defined(__arm__) || defined(_M_ARM)      // ARM-specific
 122     const int bit = ((int)(split - value) >> 31) & 1;
 123     if (value > split) {
 124       range -= split + 1;
 125       br->value_ -= (bit_t)(split + 1) << pos;
 126     } else {
 127       range = split;
 128     }
 129 #else  // faster version on x86
 130     int bit;  // Don't use 'const int bit = (value > split);", it's slower.
 131     if (value > split) {
 132       range -= split + 1;
 133       br->value_ -= (bit_t)(split + 1) << pos;
 134       bit = 1;
 135     } else {
 136       range = split;
 137       bit = 0;
 138     }
 139 #endif
 140     if (range <= (range_t)0x7e) {
 141       const int shift = kVP8Log2Range[range];
 142       range = kVP8NewRange[range];
 143       br->bits_ -= shift;
 144     }
 145     br->range_ = range;
 146     return bit;
 147   }
 148 }
 149
 150 // simplified version of VP8GetBit() for prob=0x80 (note shift is always 1 here)
 151 static WEBP_INLINE int VP8GetSigned(VP8BitReader* const br, int v) {
 152   if (br->bits_ < 0) {
 153     VP8LoadNewBytes(br);
 154   }
 155   {
 156     const int pos = br->bits_;
 157     const range_t split = br->range_ >> 1;
 158     const range_t value = (range_t)(br->value_ >> pos);
 159     const int32_t mask = (int32_t)(split - value) >> 31;  // -1 or 0
 160     br->bits_ -= 1;
 161     br->range_ += mask;
 162     br->range_ |= 1;
 163     br->value_ -= (bit_t)((split + 1) & mask) << pos;
 164     return (v ^ mask) - mask;
 165   }
 166 }
 167
 168 #ifdef __cplusplus
 169 }    // extern "C"
 170 #endif
 171
 172 #endif   // WEBP_UTILS_BIT_READER_INL_H_