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
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 range_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
VP8LoadNewBytes(VP8BitReader * const br)57 static 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!
VP8GetBit(VP8BitReader * const br,int prob)108 static 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)
VP8GetSigned(VP8BitReader * const br,int v)150 static 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