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Diffstat (limited to 'src/3rdparty/libwebp/src/utils/bit_reader_utils.h')
| -rw-r--r-- | src/3rdparty/libwebp/src/utils/bit_reader_utils.h | 174 |
1 files changed, 174 insertions, 0 deletions
diff --git a/src/3rdparty/libwebp/src/utils/bit_reader_utils.h b/src/3rdparty/libwebp/src/utils/bit_reader_utils.h new file mode 100644 index 0000000..ec3426c --- /dev/null +++ b/src/3rdparty/libwebp/src/utils/bit_reader_utils.h @@ -0,0 +1,174 @@ +// Copyright 2010 Google Inc. All Rights Reserved. +// +// Use of this source code is governed by a BSD-style license +// that can be found in the COPYING file in the root of the source +// tree. An additional intellectual property rights grant can be found +// in the file PATENTS. All contributing project authors may +// be found in the AUTHORS file in the root of the source tree. +// ----------------------------------------------------------------------------- +// +// Boolean decoder +// +// Author: Skal (pascal.massimino@gmail.com) +// Vikas Arora (vikaas.arora@gmail.com) + +#ifndef WEBP_UTILS_BIT_READER_H_ +#define WEBP_UTILS_BIT_READER_H_ + +#include <assert.h> +#ifdef _MSC_VER +#include <stdlib.h> // _byteswap_ulong +#endif +#include "../webp/types.h" + +#ifdef __cplusplus +extern "C" { +#endif + +// The Boolean decoder needs to maintain infinite precision on the value_ field. +// However, since range_ is only 8bit, we only need an active window of 8 bits +// for value_. Left bits (MSB) gets zeroed and shifted away when value_ falls +// below 128, range_ is updated, and fresh bits read from the bitstream are +// brought in as LSB. To avoid reading the fresh bits one by one (slow), we +// cache BITS of them ahead. The total of (BITS + 8) bits must fit into a +// natural register (with type bit_t). To fetch BITS bits from bitstream we +// use a type lbit_t. +// +// BITS can be any multiple of 8 from 8 to 56 (inclusive). +// Pick values that fit natural register size. + +#if defined(__i386__) || defined(_M_IX86) // x86 32bit +#define BITS 24 +#elif defined(__x86_64__) || defined(_M_X64) // x86 64bit +#define BITS 56 +#elif defined(__arm__) || defined(_M_ARM) // ARM +#define BITS 24 +#elif defined(__aarch64__) // ARM 64bit +#define BITS 56 +#elif defined(__mips__) // MIPS +#define BITS 24 +#else // reasonable default +#define BITS 24 +#endif + +//------------------------------------------------------------------------------ +// Derived types and constants: +// bit_t = natural register type for storing 'value_' (which is BITS+8 bits) +// range_t = register for 'range_' (which is 8bits only) + +#if (BITS > 24) +typedef uint64_t bit_t; +#else +typedef uint32_t bit_t; +#endif + +typedef uint32_t range_t; + +//------------------------------------------------------------------------------ +// Bitreader + +typedef struct VP8BitReader VP8BitReader; +struct VP8BitReader { + // boolean decoder (keep the field ordering as is!) + bit_t value_; // current value + range_t range_; // current range minus 1. In [127, 254] interval. + int bits_; // number of valid bits left + // read buffer + const uint8_t* buf_; // next byte to be read + const uint8_t* buf_end_; // end of read buffer + const uint8_t* buf_max_; // max packed-read position on buffer + int eof_; // true if input is exhausted +}; + +// Initialize the bit reader and the boolean decoder. +void VP8InitBitReader(VP8BitReader* const br, + const uint8_t* const start, size_t size); +// Sets the working read buffer. +void VP8BitReaderSetBuffer(VP8BitReader* const br, + const uint8_t* const start, size_t size); + +// Update internal pointers to displace the byte buffer by the +// relative offset 'offset'. +void VP8RemapBitReader(VP8BitReader* const br, ptrdiff_t offset); + +// return the next value made of 'num_bits' bits +uint32_t VP8GetValue(VP8BitReader* const br, int num_bits); +static WEBP_INLINE uint32_t VP8Get(VP8BitReader* const br) { + return VP8GetValue(br, 1); +} + +// return the next value with sign-extension. +int32_t VP8GetSignedValue(VP8BitReader* const br, int num_bits); + +// bit_reader_inl.h will implement the following methods: +// static WEBP_INLINE int VP8GetBit(VP8BitReader* const br, int prob) +// static WEBP_INLINE int VP8GetSigned(VP8BitReader* const br, int v) +// and should be included by the .c files that actually need them. +// This is to avoid recompiling the whole library whenever this file is touched, +// and also allowing platform-specific ad-hoc hacks. + +// ----------------------------------------------------------------------------- +// Bitreader for lossless format + +// maximum number of bits (inclusive) the bit-reader can handle: +#define VP8L_MAX_NUM_BIT_READ 24 + +#define VP8L_LBITS 64 // Number of bits prefetched (= bit-size of vp8l_val_t). +#define VP8L_WBITS 32 // Minimum number of bytes ready after VP8LFillBitWindow. + +typedef uint64_t vp8l_val_t; // right now, this bit-reader can only use 64bit. + +typedef struct { + vp8l_val_t val_; // pre-fetched bits + const uint8_t* buf_; // input byte buffer + size_t len_; // buffer length + size_t pos_; // byte position in buf_ + int bit_pos_; // current bit-reading position in val_ + int eos_; // true if a bit was read past the end of buffer +} VP8LBitReader; + +void VP8LInitBitReader(VP8LBitReader* const br, + const uint8_t* const start, + size_t length); + +// Sets a new data buffer. +void VP8LBitReaderSetBuffer(VP8LBitReader* const br, + const uint8_t* const buffer, size_t length); + +// Reads the specified number of bits from read buffer. +// Flags an error in case end_of_stream or n_bits is more than the allowed limit +// of VP8L_MAX_NUM_BIT_READ (inclusive). +// Flags eos_ if this read attempt is going to cross the read buffer. +uint32_t VP8LReadBits(VP8LBitReader* const br, int n_bits); + +// Return the prefetched bits, so they can be looked up. +static WEBP_INLINE uint32_t VP8LPrefetchBits(VP8LBitReader* const br) { + return (uint32_t)(br->val_ >> (br->bit_pos_ & (VP8L_LBITS - 1))); +} + +// Returns true if there was an attempt at reading bit past the end of +// the buffer. Doesn't set br->eos_ flag. +static WEBP_INLINE int VP8LIsEndOfStream(const VP8LBitReader* const br) { + assert(br->pos_ <= br->len_); + return br->eos_ || ((br->pos_ == br->len_) && (br->bit_pos_ > VP8L_LBITS)); +} + +// For jumping over a number of bits in the bit stream when accessed with +// VP8LPrefetchBits and VP8LFillBitWindow. +static WEBP_INLINE void VP8LSetBitPos(VP8LBitReader* const br, int val) { + br->bit_pos_ = val; + br->eos_ = VP8LIsEndOfStream(br); +} + +// Advances the read buffer by 4 bytes to make room for reading next 32 bits. +// Speed critical, but infrequent part of the code can be non-inlined. +extern void VP8LDoFillBitWindow(VP8LBitReader* const br); +static WEBP_INLINE void VP8LFillBitWindow(VP8LBitReader* const br) { + if (br->bit_pos_ >= VP8L_WBITS) VP8LDoFillBitWindow(br); +} + +#ifdef __cplusplus +} // extern "C" +#endif + +#endif /* WEBP_UTILS_BIT_READER_H_ */ |