// 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_UTILS_H_ #define WEBP_UTILS_BIT_READER_UTILS_H_ #include <assert.h> #ifdef _MSC_VER #include <stdlib.h> // _byteswap_ulong #endif #include "src/webp/types.h" // Warning! This macro triggers quite some MACRO wizardry around func signature! #if !defined(BITTRACE) #define BITTRACE 0 // 0 = off, 1 = print bits, 2 = print bytes #endif #if (BITTRACE > 0) struct VP8BitReader; extern void BitTrace(const struct VP8BitReader* const br, const char label[]); #define BT_TRACK(br) BitTrace(br, label) #define VP8Get(BR, L) VP8GetValue(BR, 1, L) #else #define BT_TRACK(br) // We'll REMOVE the 'const char label[]' from all signatures and calls (!!): #define VP8GetValue(BR, N, L) VP8GetValue(BR, N) #define VP8Get(BR, L) VP8GetValue(BR, 1, L) #define VP8GetSignedValue(BR, N, L) VP8GetSignedValue(BR, N) #define VP8GetBit(BR, P, L) VP8GetBit(BR, P) #define VP8GetBitAlt(BR, P, L) VP8GetBitAlt(BR, P) #define VP8GetSigned(BR, V, L) VP8GetSigned(BR, V) #endif #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, const char label[]); // return the next value with sign-extension. int32_t VP8GetSignedValue(VP8BitReader* const br, int num_bits, const char label[]); // 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. // This function does *not* set br->eos_, since it's speed-critical. // Use with extreme care! static WEBP_INLINE void VP8LSetBitPos(VP8LBitReader* const br, int val) { br->bit_pos_ = val; } // 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_UTILS_H_