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
VP8LoadNewBytes(VP8BitReader * const br)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!
VP8GetBit(VP8BitReader * const br,int prob)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)
VP8GetSigned(VP8BitReader * const br,int v)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