172 lines
5 KiB
C
172 lines
5 KiB
C
// Copyright 2014 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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// Specific inlined methods for boolean decoder [VP8GetBit() ...]
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// This file should be included by the .c sources that actually need to call
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// these methods.
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//
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// Author: Skal (pascal.massimino@gmail.com)
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#ifndef WEBP_UTILS_BIT_READER_INL_H_
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#define WEBP_UTILS_BIT_READER_INL_H_
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#ifdef HAVE_CONFIG_H
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#include "webp/config.h"
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#endif
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#ifdef WEBP_FORCE_ALIGNED
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#include <string.h> // memcpy
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#endif
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#include "../dsp/dsp.h"
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#include "./bit_reader.h"
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#include "./endian_inl.h"
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#ifdef __cplusplus
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extern "C" {
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#endif
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//------------------------------------------------------------------------------
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// Derived type lbit_t = natural type for memory I/O
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#if (BITS > 32)
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typedef uint64_t lbit_t;
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#elif (BITS > 16)
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typedef uint32_t lbit_t;
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#elif (BITS > 8)
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typedef uint16_t lbit_t;
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#else
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typedef uint8_t lbit_t;
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#endif
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extern const uint8_t kVP8Log2Range[128];
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extern const uint8_t kVP8NewRange[128];
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// special case for the tail byte-reading
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void VP8LoadFinalBytes(VP8BitReader* const br);
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//------------------------------------------------------------------------------
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// Inlined critical functions
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// makes sure br->value_ has at least BITS bits worth of data
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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_ < br->buf_max_) {
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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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#if defined(WEBP_FORCE_ALIGNED)
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lbit_t in_bits;
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memcpy(&in_bits, br->buf_, sizeof(in_bits));
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#elif defined(WEBP_USE_MIPS32)
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// This is needed because of un-aligned read.
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lbit_t in_bits;
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lbit_t* p_buf_ = (lbit_t*)br->buf_;
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__asm__ volatile(
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".set push \n\t"
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".set at \n\t"
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".set macro \n\t"
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"ulw %[in_bits], 0(%[p_buf_]) \n\t"
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".set pop \n\t"
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: [in_bits]"=r"(in_bits)
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: [p_buf_]"r"(p_buf_)
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: "memory", "at"
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);
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#else
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const lbit_t in_bits = *(const lbit_t*)br->buf_;
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#endif
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br->buf_ += BITS >> 3;
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#if !defined(WORDS_BIGENDIAN)
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#if (BITS > 32)
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bits = BSwap64(in_bits);
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bits >>= 64 - BITS;
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#elif (BITS >= 24)
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bits = BSwap32(in_bits);
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bits >>= (32 - BITS);
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#elif (BITS == 16)
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bits = BSwap16(in_bits);
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#else // BITS == 8
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bits = (bit_t)in_bits;
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#endif // BITS > 32
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#else // WORDS_BIGENDIAN
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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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br->value_ = bits | (br->value_ << BITS);
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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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// Read a bit with proba 'prob'. Speed-critical function!
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static WEBP_INLINE int VP8GetBit(VP8BitReader* const br, int prob) {
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// Don't move this declaration! It makes a big speed difference to store
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// 'range' *before* calling VP8LoadNewBytes(), even if this function doesn't
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// alter br->range_ value.
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range_t range = br->range_;
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if (br->bits_ < 0) {
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VP8LoadNewBytes(br);
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}
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{
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const int pos = br->bits_;
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const range_t split = (range * prob) >> 8;
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const range_t value = (range_t)(br->value_ >> pos);
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#if defined(__arm__) || defined(_M_ARM) // ARM-specific
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const int bit = ((int)(split - value) >> 31) & 1;
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if (value > split) {
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range -= split + 1;
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br->value_ -= (bit_t)(split + 1) << pos;
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} else {
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range = split;
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}
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#else // faster version on x86
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int bit; // Don't use 'const int bit = (value > split);", it's slower.
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if (value > split) {
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range -= split + 1;
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br->value_ -= (bit_t)(split + 1) << pos;
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bit = 1;
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} else {
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range = split;
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bit = 0;
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}
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#endif
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if (range <= (range_t)0x7e) {
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const int shift = kVP8Log2Range[range];
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range = kVP8NewRange[range];
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br->bits_ -= shift;
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}
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br->range_ = range;
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return bit;
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}
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}
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// simplified version of VP8GetBit() for prob=0x80 (note shift is always 1 here)
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static WEBP_INLINE int VP8GetSigned(VP8BitReader* const br, int v) {
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if (br->bits_ < 0) {
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VP8LoadNewBytes(br);
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}
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{
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const int pos = br->bits_;
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const range_t split = br->range_ >> 1;
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const range_t value = (range_t)(br->value_ >> pos);
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const int32_t mask = (int32_t)(split - value) >> 31; // -1 or 0
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br->bits_ -= 1;
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br->range_ += mask;
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br->range_ |= 1;
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br->value_ -= (bit_t)((split + 1) & mask) << pos;
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return (v ^ mask) - mask;
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}
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}
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#ifdef __cplusplus
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} // extern "C"
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#endif
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#endif // WEBP_UTILS_BIT_READER_INL_H_
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