// Copyright 2010 Google Inc. All Rights Reserved. // // This code is licensed under the same terms as WebM: // Software License Agreement: http://www.webmproject.org/license/software/ // Additional IP Rights Grant: http://www.webmproject.org/license/additional/ // ----------------------------------------------------------------------------- // // 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 #ifdef _MSC_VER #include // _byteswap_ulong #endif #include // For memcpy #include "../webp/types.h" #if defined(__cplusplus) || defined(c_plusplus) 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 a few of them // ahead (actually, we cache BITS of them ahead. See below). There's two // strategies regarding how to shift these looked-ahead fresh bits into the // 8bit window of value_: either we shift them in, while keeping the position of // the window fixed. Or we slide the window to the right while keeping the cache // bits at a fixed, right-justified, position. // // Example, for BITS=16: here is the content of value_ for both strategies: // // !USE_RIGHT_JUSTIFY || USE_RIGHT_JUSTIFY // || // <- 8b -><- 8b -><- BITS bits -> || <- 8b+3b -><- 8b -><- 13 bits -> // [unused][value_][cached bits][0] || [unused...][value_][cached bits] // [........00vvvvvvBBBBBBBBBBBBB000]LSB || [...........00vvvvvvBBBBBBBBBBBBB] // || // After calling VP8Shift(), where we need to shift away two zeros: // [........vvvvvvvvBBBBBBBBBBB00000]LSB || [.............vvvvvvvvBBBBBBBBBBB] // || // Just before we need to call VP8LoadNewBytes(), the situation is: // [........vvvvvv000000000000000000]LSB || [..........................vvvvvv] // || // And just after calling VP8LoadNewBytes(): // [........vvvvvvvvBBBBBBBBBBBBBBBB]LSB || [........vvvvvvvvBBBBBBBBBBBBBBBB] // // -> we're back to height active 'value_' bits (marked 'v') and BITS cached // bits (marked 'B') // // The right-justify strategy tends to use less shifts and is often faster. //------------------------------------------------------------------------------ // BITS can be any multiple of 8 from 8 to 56 (inclusive). // Pick values that fit natural register size. #if !defined(WEBP_REFERENCE_IMPLEMENTATION) #define USE_RIGHT_JUSTIFY #if defined(__i386__) || defined(_M_IX86) // x86 32bit #define BITS 16 #elif defined(__x86_64__) || defined(_M_X64) // x86 64bit #define BITS 56 #elif defined(__arm__) || defined(_M_ARM) // ARM #define BITS 24 #else // reasonable default #define BITS 24 #endif #else // reference choices #define USE_RIGHT_JUSTIFY #define BITS 8 #endif //------------------------------------------------------------------------------ // Derived types and constants // bit_t = natural register type // lbit_t = natural type for memory I/O #if (BITS > 32) typedef uint64_t bit_t; typedef uint64_t lbit_t; #elif (BITS == 32) typedef uint64_t bit_t; typedef uint32_t lbit_t; #elif (BITS == 24) typedef uint32_t bit_t; typedef uint32_t lbit_t; #elif (BITS == 16) typedef uint32_t bit_t; typedef uint16_t lbit_t; #else typedef uint32_t bit_t; typedef uint8_t lbit_t; #endif #ifndef USE_RIGHT_JUSTIFY typedef bit_t range_t; // type for storing range_ #define MASK ((((bit_t)1) << (BITS)) - 1) #else typedef uint32_t range_t; // range_ only uses 8bits here. No need for bit_t. #endif //------------------------------------------------------------------------------ // Bitreader typedef struct VP8BitReader VP8BitReader; struct VP8BitReader { const uint8_t* buf_; // next byte to be read const uint8_t* buf_end_; // end of read buffer int eof_; // true if input is exhausted // boolean decoder range_t range_; // current range minus 1. In [127, 254] interval. bit_t value_; // current value int bits_; // number of valid bits left }; // Initialize the bit reader and the boolean decoder. void VP8InitBitReader(VP8BitReader* const br, const uint8_t* const start, const uint8_t* const end); // 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); // Read a bit with proba 'prob'. Speed-critical function! extern const uint8_t kVP8Log2Range[128]; extern const range_t kVP8NewRange[128]; void VP8LoadFinalBytes(VP8BitReader* const br); // special case for the tail static WEBP_INLINE void VP8LoadNewBytes(VP8BitReader* const br) { assert(br != NULL && br->buf_ != NULL); // Read 'BITS' bits at a time if possible. if (br->buf_ + sizeof(lbit_t) <= br->buf_end_) { // convert memory type to register type (with some zero'ing!) bit_t bits; lbit_t in_bits = *(lbit_t*)br->buf_; br->buf_ += (BITS) >> 3; #if !defined(__BIG_ENDIAN__) #if (BITS > 32) // gcc 4.3 has builtin functions for swap32/swap64 #if defined(__GNUC__) && \ (__GNUC__ > 4 || (__GNUC__ == 4 && __GNUC_MINOR__ >= 3)) bits = (bit_t)__builtin_bswap64(in_bits); #elif defined(_MSC_VER) bits = (bit_t)_byteswap_uint64(in_bits); #elif defined(__x86_64__) __asm__ volatile("bswapq %0" : "=r"(bits) : "0"(in_bits)); #else // generic code for swapping 64-bit values (suggested by bdb@) bits = (bit_t)in_bits; bits = ((bits & 0xffffffff00000000ull) >> 32) | ((bits & 0x00000000ffffffffull) << 32); bits = ((bits & 0xffff0000ffff0000ull) >> 16) | ((bits & 0x0000ffff0000ffffull) << 16); bits = ((bits & 0xff00ff00ff00ff00ull) >> 8) | ((bits & 0x00ff00ff00ff00ffull) << 8); #endif bits >>= 64 - BITS; #elif (BITS >= 24) #if defined(__i386__) || defined(__x86_64__) __asm__ volatile("bswap %k0" : "=r"(in_bits) : "0"(in_bits)); bits = (bit_t)in_bits; // 24b/32b -> 32b/64b zero-extension #elif defined(_MSC_VER) bits = (bit_t)_byteswap_ulong(in_bits); #else bits = (bit_t)(in_bits >> 24) | ((in_bits >> 8) & 0xff00) | ((in_bits << 8) & 0xff0000) | (in_bits << 24); #endif // x86 bits >>= (32 - BITS); #elif (BITS == 16) // gcc will recognize a 'rorw $8, ...' here: bits = (bit_t)(in_bits >> 8) | ((in_bits & 0xff) << 8); #else // BITS == 8 bits = (bit_t)in_bits; #endif #else // BIG_ENDIAN bits = (bit_t)in_bits; #endif #ifndef USE_RIGHT_JUSTIFY br->value_ |= bits << (-br->bits_); #else br->value_ = bits | (br->value_ << (BITS)); #endif br->bits_ += (BITS); } else { VP8LoadFinalBytes(br); // no need to be inlined } } static WEBP_INLINE int VP8BitUpdate(VP8BitReader* const br, range_t split) { if (br->bits_ < 0) { // Make sure we have a least BITS bits in 'value_' VP8LoadNewBytes(br); } #ifndef USE_RIGHT_JUSTIFY split |= (MASK); if (br->value_ > split) { br->range_ -= split + 1; br->value_ -= split + 1; return 1; } else { br->range_ = split; return 0; } #else { const int pos = br->bits_; const range_t value = (range_t)(br->value_ >> pos); if (value > split) { br->range_ -= split + 1; br->value_ -= (bit_t)(split + 1) << pos; return 1; } else { br->range_ = split; return 0; } } #endif } static WEBP_INLINE void VP8Shift(VP8BitReader* const br) { #ifndef USE_RIGHT_JUSTIFY // range_ is in [0..127] interval here. const bit_t idx = br->range_ >> (BITS); const int shift = kVP8Log2Range[idx]; br->range_ = kVP8NewRange[idx]; br->value_ <<= shift; br->bits_ -= shift; #else const int shift = kVP8Log2Range[br->range_]; assert(br->range_ < (range_t)128); br->range_ = kVP8NewRange[br->range_]; br->bits_ -= shift; #endif } static WEBP_INLINE int VP8GetBit(VP8BitReader* const br, int prob) { #ifndef USE_RIGHT_JUSTIFY // It's important to avoid generating a 64bit x 64bit multiply here. // We just need an 8b x 8b after all. const range_t split = (range_t)((uint32_t)(br->range_ >> (BITS)) * prob) << ((BITS) - 8); const int bit = VP8BitUpdate(br, split); if (br->range_ <= (((range_t)0x7e << (BITS)) | (MASK))) { VP8Shift(br); } return bit; #else const range_t split = (br->range_ * prob) >> 8; const int bit = VP8BitUpdate(br, split); if (br->range_ <= (range_t)0x7e) { VP8Shift(br); } return bit; #endif } static WEBP_INLINE int VP8GetSigned(VP8BitReader* const br, int v) { const range_t split = (br->range_ >> 1); const int bit = VP8BitUpdate(br, split); VP8Shift(br); return bit ? -v : v; } // ----------------------------------------------------------------------------- // Bitreader for lossless format 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_; // bitstream is finished int error_; // an error occurred (buffer overflow attempt...) } 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 allowed limit. // 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_); } // Discard 'num_bits' bits from the cache. static WEBP_INLINE void VP8LDiscardBits(VP8LBitReader* const br, int num_bits) { br->bit_pos_ += num_bits; } // Advances the Read buffer by 4 bytes to make room for reading next 32 bits. void VP8LFillBitWindow(VP8LBitReader* const br); #if defined(__cplusplus) || defined(c_plusplus) } // extern "C" #endif #endif /* WEBP_UTILS_BIT_READER_H_ */