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 "./bit_reader.h"
28#include "./endian_inl.h"
29
30#ifdef __cplusplus
31extern "C" {
32#endif
33
34//------------------------------------------------------------------------------
35// Derived type lbit_t = natural type for memory I/O
36
37#if   (BITS > 32)
38typedef uint64_t lbit_t;
39#elif (BITS > 16)
40typedef uint32_t lbit_t;
41#elif (BITS >  8)
42typedef uint16_t lbit_t;
43#else
44typedef uint8_t lbit_t;
45#endif
46
47extern const uint8_t kVP8Log2Range[128];
48extern const range_t kVP8NewRange[128];
49
50// special case for the tail byte-reading
51void VP8LoadFinalBytes(VP8BitReader* const br);
52
53//------------------------------------------------------------------------------
54// Inlined critical functions
55
56// makes sure br->value_ has at least BITS bits worth of data
57static WEBP_INLINE void VP8LoadNewBytes(VP8BitReader* const br) {
58  assert(br != NULL && br->buf_ != NULL);
59  // Read 'BITS' bits at a time if possible.
60  if (br->buf_ + sizeof(lbit_t) <= br->buf_end_) {
61    // convert memory type to register type (with some zero'ing!)
62    bit_t bits;
63#if defined(WEBP_FORCE_ALIGNED)
64    lbit_t in_bits;
65    memcpy(&in_bits, br->buf_, sizeof(in_bits));
66#elif defined(__mips__) && !defined(__mips64)  // MIPS
67    // This is needed because of un-aligned read.
68    lbit_t in_bits;
69    lbit_t* p_buf_ = (lbit_t*)br->buf_;
70    __asm__ volatile(
71      ".set   push                             \n\t"
72      ".set   at                               \n\t"
73      ".set   macro                            \n\t"
74      "ulw    %[in_bits], 0(%[p_buf_])         \n\t"
75      ".set   pop                              \n\t"
76      : [in_bits]"=r"(in_bits)
77      : [p_buf_]"r"(p_buf_)
78      : "memory", "at"
79    );
80#else
81    const lbit_t in_bits = *(const lbit_t*)br->buf_;
82#endif
83    br->buf_ += BITS >> 3;
84#if !defined(WORDS_BIGENDIAN)
85#if (BITS > 32)
86    bits = BSwap64(in_bits);
87    bits >>= 64 - BITS;
88#elif (BITS >= 24)
89    bits = BSwap32(in_bits);
90    bits >>= (32 - BITS);
91#elif (BITS == 16)
92    bits = BSwap16(in_bits);
93#else   // BITS == 8
94    bits = (bit_t)in_bits;
95#endif  // BITS > 32
96#else    // WORDS_BIGENDIAN
97    bits = (bit_t)in_bits;
98    if (BITS != 8 * sizeof(bit_t)) bits >>= (8 * sizeof(bit_t) - BITS);
99#endif
100    br->value_ = bits | (br->value_ << BITS);
101    br->bits_ += BITS;
102  } else {
103    VP8LoadFinalBytes(br);    // no need to be inlined
104  }
105}
106
107// Read a bit with proba 'prob'. Speed-critical function!
108static WEBP_INLINE int VP8GetBit(VP8BitReader* const br, int prob) {
109  // Don't move this declaration! It makes a big speed difference to store
110  // 'range' *before* calling VP8LoadNewBytes(), even if this function doesn't
111  // alter br->range_ value.
112  range_t range = br->range_;
113  if (br->bits_ < 0) {
114    VP8LoadNewBytes(br);
115  }
116  {
117    const int pos = br->bits_;
118    const range_t split = (range * prob) >> 8;
119    const range_t value = (range_t)(br->value_ >> pos);
120#if defined(__arm__) || defined(_M_ARM)      // ARM-specific
121    const int bit = ((int)(split - value) >> 31) & 1;
122    if (value > split) {
123      range -= split + 1;
124      br->value_ -= (bit_t)(split + 1) << pos;
125    } else {
126      range = split;
127    }
128#else  // faster version on x86
129    int bit;  // Don't use 'const int bit = (value > split);", it's slower.
130    if (value > split) {
131      range -= split + 1;
132      br->value_ -= (bit_t)(split + 1) << pos;
133      bit = 1;
134    } else {
135      range = split;
136      bit = 0;
137    }
138#endif
139    if (range <= (range_t)0x7e) {
140      const int shift = kVP8Log2Range[range];
141      range = kVP8NewRange[range];
142      br->bits_ -= shift;
143    }
144    br->range_ = range;
145    return bit;
146  }
147}
148
149// simplified version of VP8GetBit() for prob=0x80 (note shift is always 1 here)
150static WEBP_INLINE int VP8GetSigned(VP8BitReader* const br, int v) {
151  if (br->bits_ < 0) {
152    VP8LoadNewBytes(br);
153  }
154  {
155    const int pos = br->bits_;
156    const range_t split = br->range_ >> 1;
157    const range_t value = (range_t)(br->value_ >> pos);
158    const int32_t mask = (int32_t)(split - value) >> 31;  // -1 or 0
159    br->bits_ -= 1;
160    br->range_ += mask;
161    br->range_ |= 1;
162    br->value_ -= (bit_t)((split + 1) & mask) << pos;
163    return (v ^ mask) - mask;
164  }
165}
166
167#ifdef __cplusplus
168}    // extern "C"
169#endif
170
171#endif   // WEBP_UTILS_BIT_READER_INL_H_
172