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 #include <string.h> // for memcpy
24
25 #include "../dsp/dsp.h"
26 #include "./bit_reader_utils.h"
27 #include "./endian_inl_utils.h"
28 #include "./utils.h"
29
30 #ifdef __cplusplus
31 extern "C" {
32 #endif
33
34 //------------------------------------------------------------------------------
35 // Derived type lbit_t = natural type for memory I/O
36
37 #if (BITS > 32)
38 typedef uint64_t lbit_t;
39 #elif (BITS > 16)
40 typedef uint32_t lbit_t;
41 #elif (BITS > 8)
42 typedef uint16_t lbit_t;
43 #else
44 typedef uint8_t lbit_t;
45 #endif
46
47 extern const uint8_t kVP8Log2Range[128];
48 extern const uint8_t kVP8NewRange[128];
49
50 // special case for the tail byte-reading
51 void VP8LoadFinalBytes(VP8BitReader* const br);
52
53 //------------------------------------------------------------------------------
54 // Inlined critical functions
55
56 // makes sure br->value_ has at least BITS bits worth of data
57 static WEBP_UBSAN_IGNORE_UNDEF WEBP_INLINE
VP8LoadNewBytes(VP8BitReader * const br)58 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_USE_MIPS32)
65 // This is needed because of un-aligned read.
66 lbit_t in_bits;
67 lbit_t* p_buf_ = (lbit_t*)br->buf_;
68 __asm__ volatile(
69 ".set push \n\t"
70 ".set at \n\t"
71 ".set macro \n\t"
72 "ulw %[in_bits], 0(%[p_buf_]) \n\t"
73 ".set pop \n\t"
74 : [in_bits]"=r"(in_bits)
75 : [p_buf_]"r"(p_buf_)
76 : "memory", "at"
77 );
78 #else
79 lbit_t in_bits;
80 memcpy(&in_bits, br->buf_, sizeof(in_bits));
81 #endif
82 br->buf_ += BITS >> 3;
83 #if !defined(WORDS_BIGENDIAN)
84 #if (BITS > 32)
85 bits = BSwap64(in_bits);
86 bits >>= 64 - BITS;
87 #elif (BITS >= 24)
88 bits = BSwap32(in_bits);
89 bits >>= (32 - BITS);
90 #elif (BITS == 16)
91 bits = BSwap16(in_bits);
92 #else // BITS == 8
93 bits = (bit_t)in_bits;
94 #endif // BITS > 32
95 #else // WORDS_BIGENDIAN
96 bits = (bit_t)in_bits;
97 if (BITS != 8 * sizeof(bit_t)) bits >>= (8 * sizeof(bit_t) - BITS);
98 #endif
99 br->value_ = bits | (br->value_ << BITS);
100 br->bits_ += BITS;
101 } else {
102 VP8LoadFinalBytes(br); // no need to be inlined
103 }
104 }
105
106 // Read a bit with proba 'prob'. Speed-critical function!
VP8GetBit(VP8BitReader * const br,int prob)107 static WEBP_INLINE int VP8GetBit(VP8BitReader* const br, int prob) {
108 // Don't move this declaration! It makes a big speed difference to store
109 // 'range' *before* calling VP8LoadNewBytes(), even if this function doesn't
110 // alter br->range_ value.
111 range_t range = br->range_;
112 if (br->bits_ < 0) {
113 VP8LoadNewBytes(br);
114 }
115 {
116 const int pos = br->bits_;
117 const range_t split = (range * prob) >> 8;
118 const range_t value = (range_t)(br->value_ >> pos);
119 const int bit = (value > split);
120 if (bit) {
121 range -= split;
122 br->value_ -= (bit_t)(split + 1) << pos;
123 } else {
124 range = split + 1;
125 }
126 {
127 const int shift = 7 ^ BitsLog2Floor(range);
128 range <<= shift;
129 br->bits_ -= shift;
130 }
131 br->range_ = range - 1;
132 return bit;
133 }
134 }
135
136 // simplified version of VP8GetBit() for prob=0x80 (note shift is always 1 here)
137 static WEBP_UBSAN_IGNORE_UNSIGNED_OVERFLOW WEBP_INLINE
VP8GetSigned(VP8BitReader * const br,int v)138 int VP8GetSigned(VP8BitReader* const br, int v) {
139 if (br->bits_ < 0) {
140 VP8LoadNewBytes(br);
141 }
142 {
143 const int pos = br->bits_;
144 const range_t split = br->range_ >> 1;
145 const range_t value = (range_t)(br->value_ >> pos);
146 const int32_t mask = (int32_t)(split - value) >> 31; // -1 or 0
147 br->bits_ -= 1;
148 br->range_ += mask;
149 br->range_ |= 1;
150 br->value_ -= (bit_t)((split + 1) & mask) << pos;
151 return (v ^ mask) - mask;
152 }
153 }
154
VP8GetBitAlt(VP8BitReader * const br,int prob)155 static WEBP_INLINE int VP8GetBitAlt(VP8BitReader* const br, int prob) {
156 // Don't move this declaration! It makes a big speed difference to store
157 // 'range' *before* calling VP8LoadNewBytes(), even if this function doesn't
158 // alter br->range_ value.
159 range_t range = br->range_;
160 if (br->bits_ < 0) {
161 VP8LoadNewBytes(br);
162 }
163 {
164 const int pos = br->bits_;
165 const range_t split = (range * prob) >> 8;
166 const range_t value = (range_t)(br->value_ >> pos);
167 int bit; // Don't use 'const int bit = (value > split);", it's slower.
168 if (value > split) {
169 range -= split + 1;
170 br->value_ -= (bit_t)(split + 1) << pos;
171 bit = 1;
172 } else {
173 range = split;
174 bit = 0;
175 }
176 if (range <= (range_t)0x7e) {
177 const int shift = kVP8Log2Range[range];
178 range = kVP8NewRange[range];
179 br->bits_ -= shift;
180 }
181 br->range_ = range;
182 return bit;
183 }
184 }
185
186 #ifdef __cplusplus
187 } // extern "C"
188 #endif
189
190 #endif // WEBP_UTILS_BIT_READER_INL_H_
191