1 // Copyright 2010 Google Inc. All Rights Reserved.
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 // -----------------------------------------------------------------------------
12 // Author: Skal (pascal.massimino@gmail.com)
14 #include "./bit_reader.h"
16 #ifndef USE_RIGHT_JUSTIFY
17 #define MK(X) (((range_t)(X) << (BITS)) | (MASK))
19 #define MK(X) ((range_t)(X))
22 //------------------------------------------------------------------------------
25 void VP8InitBitReader(VP8BitReader* const br,
26 const uint8_t* const start, const uint8_t* const end) {
28 assert(start != NULL);
30 br->range_ = MK(255 - 1);
34 br->bits_ = -8; // to load the very first 8bits
38 const uint8_t kVP8Log2Range[128] = {
39 7, 6, 6, 5, 5, 5, 5, 4, 4, 4, 4, 4, 4, 4, 4,
40 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3,
41 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2,
42 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2,
43 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,
44 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,
45 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,
46 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,
50 // range = (range << kVP8Log2Range[range]) + trailing 1's
51 const range_t kVP8NewRange[128] = {
52 MK(127), MK(127), MK(191), MK(127), MK(159), MK(191), MK(223), MK(127),
53 MK(143), MK(159), MK(175), MK(191), MK(207), MK(223), MK(239), MK(127),
54 MK(135), MK(143), MK(151), MK(159), MK(167), MK(175), MK(183), MK(191),
55 MK(199), MK(207), MK(215), MK(223), MK(231), MK(239), MK(247), MK(127),
56 MK(131), MK(135), MK(139), MK(143), MK(147), MK(151), MK(155), MK(159),
57 MK(163), MK(167), MK(171), MK(175), MK(179), MK(183), MK(187), MK(191),
58 MK(195), MK(199), MK(203), MK(207), MK(211), MK(215), MK(219), MK(223),
59 MK(227), MK(231), MK(235), MK(239), MK(243), MK(247), MK(251), MK(127),
60 MK(129), MK(131), MK(133), MK(135), MK(137), MK(139), MK(141), MK(143),
61 MK(145), MK(147), MK(149), MK(151), MK(153), MK(155), MK(157), MK(159),
62 MK(161), MK(163), MK(165), MK(167), MK(169), MK(171), MK(173), MK(175),
63 MK(177), MK(179), MK(181), MK(183), MK(185), MK(187), MK(189), MK(191),
64 MK(193), MK(195), MK(197), MK(199), MK(201), MK(203), MK(205), MK(207),
65 MK(209), MK(211), MK(213), MK(215), MK(217), MK(219), MK(221), MK(223),
66 MK(225), MK(227), MK(229), MK(231), MK(233), MK(235), MK(237), MK(239),
67 MK(241), MK(243), MK(245), MK(247), MK(249), MK(251), MK(253), MK(127)
72 void VP8LoadFinalBytes(VP8BitReader* const br) {
73 assert(br != NULL && br->buf_ != NULL);
74 // Only read 8bits at a time
75 if (br->buf_ < br->buf_end_) {
76 #ifndef USE_RIGHT_JUSTIFY
77 br->value_ |= (bit_t)(*br->buf_++) << ((BITS) - 8 - br->bits_);
79 br->value_ = (bit_t)(*br->buf_++) | (br->value_ << 8);
82 } else if (!br->eof_) {
83 #ifdef USE_RIGHT_JUSTIFY
84 // These are not strictly needed, but it makes the behaviour
85 // consistent for both USE_RIGHT_JUSTIFY and !USE_RIGHT_JUSTIFY.
93 //------------------------------------------------------------------------------
96 uint32_t VP8GetValue(VP8BitReader* const br, int bits) {
99 v |= VP8GetBit(br, 0x80) << bits;
104 int32_t VP8GetSignedValue(VP8BitReader* const br, int bits) {
105 const int value = VP8GetValue(br, bits);
106 return VP8Get(br) ? -value : value;
109 //------------------------------------------------------------------------------
112 #define MAX_NUM_BIT_READ 25
114 #define LBITS 64 // Number of bits prefetched.
115 #define WBITS 32 // Minimum number of bytes needed after VP8LFillBitWindow.
116 #define LOG8_WBITS 4 // Number of bytes needed to store WBITS bits.
118 static const uint32_t kBitMask[MAX_NUM_BIT_READ] = {
119 0, 1, 3, 7, 15, 31, 63, 127, 255, 511, 1023, 2047, 4095, 8191, 16383, 32767,
120 65535, 131071, 262143, 524287, 1048575, 2097151, 4194303, 8388607, 16777215
123 void VP8LInitBitReader(VP8LBitReader* const br,
124 const uint8_t* const start,
128 assert(start != NULL);
129 assert(length < 0xfffffff8u); // can't happen with a RIFF chunk.
138 for (i = 0; i < sizeof(br->val_) && i < br->len_; ++i) {
139 br->val_ |= ((vp8l_val_t)br->buf_[br->pos_]) << (8 * i);
144 // Special version that assumes br->pos_ <= br_len_.
145 static int IsEndOfStreamSpecial(const VP8LBitReader* const br) {
146 assert(br->pos_ <= br->len_);
147 return br->pos_ == br->len_ && br->bit_pos_ >= LBITS;
150 static int IsEndOfStream(const VP8LBitReader* const br) {
151 return (br->pos_ > br->len_) || IsEndOfStreamSpecial(br);
154 void VP8LBitReaderSetBuffer(VP8LBitReader* const br,
155 const uint8_t* const buf, size_t len) {
158 assert(len < 0xfffffff8u); // can't happen with a RIFF chunk.
161 br->eos_ = IsEndOfStream(br);
164 // If not at EOS, reload up to LBITS byte-by-byte
165 static void ShiftBytes(VP8LBitReader* const br) {
166 while (br->bit_pos_ >= 8 && br->pos_ < br->len_) {
168 br->val_ |= ((vp8l_val_t)br->buf_[br->pos_]) << (LBITS - 8);
174 void VP8LFillBitWindow(VP8LBitReader* const br) {
175 if (br->bit_pos_ >= WBITS) {
176 #if (defined(__x86_64__) || defined(_M_X64))
177 if (br->pos_ + sizeof(br->val_) < br->len_) {
179 br->bit_pos_ -= WBITS;
180 // The expression below needs a little-endian arch to work correctly.
181 // This gives a large speedup for decoding speed.
182 br->val_ |= *(const vp8l_val_t*)(br->buf_ + br->pos_) << (LBITS - WBITS);
183 br->pos_ += LOG8_WBITS;
187 ShiftBytes(br); // Slow path.
188 br->eos_ = IsEndOfStreamSpecial(br);
192 uint32_t VP8LReadBits(VP8LBitReader* const br, int n_bits) {
194 // Flag an error if end_of_stream or n_bits is more than allowed limit.
195 if (!br->eos_ && n_bits < MAX_NUM_BIT_READ) {
197 (uint32_t)(br->val_ >> br->bit_pos_) & kBitMask[n_bits];
198 const int new_bits = br->bit_pos_ + n_bits;
199 br->bit_pos_ = new_bits;
200 // If this read is going to cross the read buffer, set the eos flag.
201 br->eos_ = IsEndOfStreamSpecial(br);
210 //------------------------------------------------------------------------------