332 lines
11 KiB
C
332 lines
11 KiB
C
// Copyright 2010 Google Inc. All Rights Reserved.
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//
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// Use of this source code is governed by a BSD-style license
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// that can be found in the COPYING file in the root of the source
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// tree. An additional intellectual property rights grant can be found
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// in the file PATENTS. All contributing project authors may
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// be found in the AUTHORS file in the root of the source tree.
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// -----------------------------------------------------------------------------
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//
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// Boolean decoder
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//
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// Author: Skal (pascal.massimino@gmail.com)
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// Vikas Arora (vikaas.arora@gmail.com)
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#ifndef WEBP_UTILS_BIT_READER_H_
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#define WEBP_UTILS_BIT_READER_H_
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#include <assert.h>
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#ifdef _MSC_VER
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#include <stdlib.h> // _byteswap_ulong
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#endif
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#include <string.h> // For memcpy
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#include "../webp/types.h"
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#if defined(__cplusplus) || defined(c_plusplus)
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extern "C" {
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#endif
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// The Boolean decoder needs to maintain infinite precision on the value_ field.
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// However, since range_ is only 8bit, we only need an active window of 8 bits
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// for value_. Left bits (MSB) gets zeroed and shifted away when value_ falls
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// below 128, range_ is updated, and fresh bits read from the bitstream are
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// brought in as LSB.
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// To avoid reading the fresh bits one by one (slow), we cache a few of them
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// ahead (actually, we cache BITS of them ahead. See below). There's two
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// strategies regarding how to shift these looked-ahead fresh bits into the
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// 8bit window of value_: either we shift them in, while keeping the position of
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// the window fixed. Or we slide the window to the right while keeping the cache
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// bits at a fixed, right-justified, position.
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//
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// Example, for BITS=16: here is the content of value_ for both strategies:
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//
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// !USE_RIGHT_JUSTIFY || USE_RIGHT_JUSTIFY
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// ||
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// <- 8b -><- 8b -><- BITS bits -> || <- 8b+3b -><- 8b -><- 13 bits ->
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// [unused][value_][cached bits][0] || [unused...][value_][cached bits]
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// [........00vvvvvvBBBBBBBBBBBBB000]LSB || [...........00vvvvvvBBBBBBBBBBBBB]
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// ||
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// After calling VP8Shift(), where we need to shift away two zeros:
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// [........vvvvvvvvBBBBBBBBBBB00000]LSB || [.............vvvvvvvvBBBBBBBBBBB]
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// ||
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// Just before we need to call VP8LoadNewBytes(), the situation is:
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// [........vvvvvv000000000000000000]LSB || [..........................vvvvvv]
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// ||
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// And just after calling VP8LoadNewBytes():
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// [........vvvvvvvvBBBBBBBBBBBBBBBB]LSB || [........vvvvvvvvBBBBBBBBBBBBBBBB]
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//
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// -> we're back to height active 'value_' bits (marked 'v') and BITS cached
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// bits (marked 'B')
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//
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// The right-justify strategy tends to use less shifts and is often faster.
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//------------------------------------------------------------------------------
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// BITS can be any multiple of 8 from 8 to 56 (inclusive).
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// Pick values that fit natural register size.
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#if !defined(WEBP_REFERENCE_IMPLEMENTATION)
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#define USE_RIGHT_JUSTIFY
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#if defined(__i386__) || defined(_M_IX86) // x86 32bit
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#define BITS 16
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#elif defined(__x86_64__) || defined(_M_X64) // x86 64bit
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#define BITS 56
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#elif defined(__arm__) || defined(_M_ARM) // ARM
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#define BITS 24
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#else // reasonable default
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#define BITS 24
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#endif
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#else // reference choices
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#define USE_RIGHT_JUSTIFY
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#define BITS 8
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#endif
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//------------------------------------------------------------------------------
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// Derived types and constants
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// bit_t = natural register type
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// lbit_t = natural type for memory I/O
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#if (BITS > 32)
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typedef uint64_t bit_t;
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typedef uint64_t lbit_t;
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#elif (BITS == 32)
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typedef uint64_t bit_t;
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typedef uint32_t lbit_t;
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#elif (BITS == 24)
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typedef uint32_t bit_t;
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typedef uint32_t lbit_t;
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#elif (BITS == 16)
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typedef uint32_t bit_t;
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typedef uint16_t lbit_t;
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#else
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typedef uint32_t bit_t;
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typedef uint8_t lbit_t;
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#endif
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#ifndef USE_RIGHT_JUSTIFY
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typedef bit_t range_t; // type for storing range_
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#define MASK ((((bit_t)1) << (BITS)) - 1)
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#else
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typedef uint32_t range_t; // range_ only uses 8bits here. No need for bit_t.
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#endif
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//------------------------------------------------------------------------------
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// Bitreader
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typedef struct VP8BitReader VP8BitReader;
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struct VP8BitReader {
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const uint8_t* buf_; // next byte to be read
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const uint8_t* buf_end_; // end of read buffer
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int eof_; // true if input is exhausted
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// boolean decoder
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range_t range_; // current range minus 1. In [127, 254] interval.
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bit_t value_; // current value
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int bits_; // number of valid bits left
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};
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// Initialize the bit reader and the boolean decoder.
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void VP8InitBitReader(VP8BitReader* const br,
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const uint8_t* const start, const uint8_t* const end);
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// return the next value made of 'num_bits' bits
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uint32_t VP8GetValue(VP8BitReader* const br, int num_bits);
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static WEBP_INLINE uint32_t VP8Get(VP8BitReader* const br) {
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return VP8GetValue(br, 1);
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}
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// return the next value with sign-extension.
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int32_t VP8GetSignedValue(VP8BitReader* const br, int num_bits);
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// Read a bit with proba 'prob'. Speed-critical function!
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extern const uint8_t kVP8Log2Range[128];
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extern const range_t kVP8NewRange[128];
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void VP8LoadFinalBytes(VP8BitReader* const br); // special case for the tail
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static WEBP_INLINE void VP8LoadNewBytes(VP8BitReader* const br) {
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assert(br != NULL && br->buf_ != NULL);
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// Read 'BITS' bits at a time if possible.
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if (br->buf_ + sizeof(lbit_t) <= br->buf_end_) {
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// convert memory type to register type (with some zero'ing!)
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bit_t bits;
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lbit_t in_bits = *(lbit_t*)br->buf_;
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br->buf_ += (BITS) >> 3;
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#if !defined(__BIG_ENDIAN__)
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#if (BITS > 32)
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// gcc 4.3 has builtin functions for swap32/swap64
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#if defined(__GNUC__) && \
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(__GNUC__ > 4 || (__GNUC__ == 4 && __GNUC_MINOR__ >= 3))
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bits = (bit_t)__builtin_bswap64(in_bits);
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#elif defined(_MSC_VER)
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bits = (bit_t)_byteswap_uint64(in_bits);
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#elif defined(__x86_64__)
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__asm__ volatile("bswapq %0" : "=r"(bits) : "0"(in_bits));
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#else // generic code for swapping 64-bit values (suggested by bdb@)
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bits = (bit_t)in_bits;
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bits = ((bits & 0xffffffff00000000ull) >> 32) |
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((bits & 0x00000000ffffffffull) << 32);
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bits = ((bits & 0xffff0000ffff0000ull) >> 16) |
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((bits & 0x0000ffff0000ffffull) << 16);
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bits = ((bits & 0xff00ff00ff00ff00ull) >> 8) |
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((bits & 0x00ff00ff00ff00ffull) << 8);
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#endif
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bits >>= 64 - BITS;
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#elif (BITS >= 24)
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#if defined(__i386__) || defined(__x86_64__)
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__asm__ volatile("bswap %k0" : "=r"(in_bits) : "0"(in_bits));
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bits = (bit_t)in_bits; // 24b/32b -> 32b/64b zero-extension
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#elif defined(_MSC_VER)
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bits = (bit_t)_byteswap_ulong(in_bits);
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#else
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bits = (bit_t)(in_bits >> 24) | ((in_bits >> 8) & 0xff00)
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| ((in_bits << 8) & 0xff0000) | (in_bits << 24);
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#endif // x86
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bits >>= (32 - BITS);
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#elif (BITS == 16)
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// gcc will recognize a 'rorw $8, ...' here:
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bits = (bit_t)(in_bits >> 8) | ((in_bits & 0xff) << 8);
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#else // BITS == 8
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bits = (bit_t)in_bits;
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#endif
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#else // BIG_ENDIAN
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bits = (bit_t)in_bits;
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if (BITS != 8 * sizeof(bit_t)) bits >>= (8 * sizeof(bit_t) - BITS);
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#endif
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#ifndef USE_RIGHT_JUSTIFY
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br->value_ |= bits << (-br->bits_);
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#else
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br->value_ = bits | (br->value_ << (BITS));
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#endif
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br->bits_ += (BITS);
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} else {
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VP8LoadFinalBytes(br); // no need to be inlined
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}
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}
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static WEBP_INLINE int VP8BitUpdate(VP8BitReader* const br, range_t split) {
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if (br->bits_ < 0) { // Make sure we have a least BITS bits in 'value_'
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VP8LoadNewBytes(br);
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}
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#ifndef USE_RIGHT_JUSTIFY
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split |= (MASK);
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if (br->value_ > split) {
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br->range_ -= split + 1;
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br->value_ -= split + 1;
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return 1;
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} else {
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br->range_ = split;
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return 0;
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}
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#else
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{
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const int pos = br->bits_;
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const range_t value = (range_t)(br->value_ >> pos);
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if (value > split) {
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br->range_ -= split + 1;
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br->value_ -= (bit_t)(split + 1) << pos;
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return 1;
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} else {
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br->range_ = split;
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return 0;
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}
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}
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#endif
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}
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static WEBP_INLINE void VP8Shift(VP8BitReader* const br) {
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#ifndef USE_RIGHT_JUSTIFY
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// range_ is in [0..127] interval here.
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const bit_t idx = br->range_ >> (BITS);
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const int shift = kVP8Log2Range[idx];
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br->range_ = kVP8NewRange[idx];
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br->value_ <<= shift;
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br->bits_ -= shift;
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#else
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const int shift = kVP8Log2Range[br->range_];
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assert(br->range_ < (range_t)128);
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br->range_ = kVP8NewRange[br->range_];
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br->bits_ -= shift;
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#endif
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}
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static WEBP_INLINE int VP8GetBit(VP8BitReader* const br, int prob) {
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#ifndef USE_RIGHT_JUSTIFY
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// It's important to avoid generating a 64bit x 64bit multiply here.
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// We just need an 8b x 8b after all.
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const range_t split =
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(range_t)((uint32_t)(br->range_ >> (BITS)) * prob) << ((BITS) - 8);
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const int bit = VP8BitUpdate(br, split);
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if (br->range_ <= (((range_t)0x7e << (BITS)) | (MASK))) {
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VP8Shift(br);
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}
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return bit;
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#else
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const range_t split = (br->range_ * prob) >> 8;
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const int bit = VP8BitUpdate(br, split);
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if (br->range_ <= (range_t)0x7e) {
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VP8Shift(br);
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}
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return bit;
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#endif
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}
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static WEBP_INLINE int VP8GetSigned(VP8BitReader* const br, int v) {
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const range_t split = (br->range_ >> 1);
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const int bit = VP8BitUpdate(br, split);
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VP8Shift(br);
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return bit ? -v : v;
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}
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// -----------------------------------------------------------------------------
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// Bitreader for lossless format
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typedef uint64_t vp8l_val_t; // right now, this bit-reader can only use 64bit.
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typedef struct {
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vp8l_val_t val_; // pre-fetched bits
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const uint8_t* buf_; // input byte buffer
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size_t len_; // buffer length
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size_t pos_; // byte position in buf_
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int bit_pos_; // current bit-reading position in val_
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int eos_; // bitstream is finished
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int error_; // an error occurred (buffer overflow attempt...)
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} VP8LBitReader;
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void VP8LInitBitReader(VP8LBitReader* const br,
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const uint8_t* const start,
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size_t length);
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// Sets a new data buffer.
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void VP8LBitReaderSetBuffer(VP8LBitReader* const br,
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const uint8_t* const buffer, size_t length);
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// Reads the specified number of bits from Read Buffer.
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// Flags an error in case end_of_stream or n_bits is more than allowed limit.
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// Flags eos if this read attempt is going to cross the read buffer.
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uint32_t VP8LReadBits(VP8LBitReader* const br, int n_bits);
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// Return the prefetched bits, so they can be looked up.
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static WEBP_INLINE uint32_t VP8LPrefetchBits(VP8LBitReader* const br) {
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return (uint32_t)(br->val_ >> br->bit_pos_);
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}
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// Discard 'num_bits' bits from the cache.
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static WEBP_INLINE void VP8LDiscardBits(VP8LBitReader* const br, int num_bits) {
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br->bit_pos_ += num_bits;
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}
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// Advances the Read buffer by 4 bytes to make room for reading next 32 bits.
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void VP8LFillBitWindow(VP8LBitReader* const br);
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#if defined(__cplusplus) || defined(c_plusplus)
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} // extern "C"
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#endif
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#endif /* WEBP_UTILS_BIT_READER_H_ */
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