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      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 (at) 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 uint8_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_ < br->buf_max_) {
     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_
    173