Source code
Revision control
Copy as Markdown
Other Tools
// Copyright 2014 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.
// -----------------------------------------------------------------------------
//
// Specific inlined methods for boolean decoder [VP8GetBit() ...]
// This file should be included by the .c sources that actually need to call
// these methods.
//
// Author: Skal (pascal.massimino@gmail.com)
#ifndef WEBP_UTILS_BIT_READER_INL_UTILS_H_
#define WEBP_UTILS_BIT_READER_INL_UTILS_H_
#ifdef HAVE_CONFIG_H
#include "src/webp/config.h"
#endif
#include <string.h> // for memcpy
#include "src/dsp/dsp.h"
#include "src/utils/bit_reader_utils.h"
#include "src/utils/endian_inl_utils.h"
#include "src/utils/utils.h"
#ifdef __cplusplus
extern "C" {
#endif
//------------------------------------------------------------------------------
// Derived type lbit_t = natural type for memory I/O
#if (BITS > 32)
typedef uint64_t lbit_t;
#elif (BITS > 16)
typedef uint32_t lbit_t;
#elif (BITS > 8)
typedef uint16_t lbit_t;
#else
typedef uint8_t lbit_t;
#endif
extern const uint8_t kVP8Log2Range[128];
extern const uint8_t kVP8NewRange[128];
// special case for the tail byte-reading
void VP8LoadFinalBytes(VP8BitReader* const br);
//------------------------------------------------------------------------------
// Inlined critical functions
// makes sure br->value_ has at least BITS bits worth of data
static WEBP_UBSAN_IGNORE_UNDEF WEBP_INLINE
void VP8LoadNewBytes(VP8BitReader* WEBP_RESTRICT const br) {
assert(br != NULL && br->buf_ != NULL);
// Read 'BITS' bits at a time if possible.
if (br->buf_ < br->buf_max_) {
// convert memory type to register type (with some zero'ing!)
bit_t bits;
#if defined(WEBP_USE_MIPS32)
// This is needed because of un-aligned read.
lbit_t in_bits;
lbit_t* p_buf_ = (lbit_t*)br->buf_;
__asm__ volatile(
".set push \n\t"
".set at \n\t"
".set macro \n\t"
"ulw %[in_bits], 0(%[p_buf_]) \n\t"
".set pop \n\t"
: [in_bits]"=r"(in_bits)
: [p_buf_]"r"(p_buf_)
: "memory", "at"
);
#else
lbit_t in_bits;
memcpy(&in_bits, br->buf_, sizeof(in_bits));
#endif
br->buf_ += BITS >> 3;
#if !defined(WORDS_BIGENDIAN)
#if (BITS > 32)
bits = BSwap64(in_bits);
bits >>= 64 - BITS;
#elif (BITS >= 24)
bits = BSwap32(in_bits);
bits >>= (32 - BITS);
#elif (BITS == 16)
bits = BSwap16(in_bits);
#else // BITS == 8
bits = (bit_t)in_bits;
#endif // BITS > 32
#else // WORDS_BIGENDIAN
bits = (bit_t)in_bits;
if (BITS != 8 * sizeof(bit_t)) bits >>= (8 * sizeof(bit_t) - BITS);
#endif
br->value_ = bits | (br->value_ << BITS);
br->bits_ += BITS;
} else {
VP8LoadFinalBytes(br); // no need to be inlined
}
}
// Read a bit with proba 'prob'. Speed-critical function!
static WEBP_INLINE int VP8GetBit(VP8BitReader* WEBP_RESTRICT const br,
int prob, const char label[]) {
// Don't move this declaration! It makes a big speed difference to store
// 'range' *before* calling VP8LoadNewBytes(), even if this function doesn't
// alter br->range_ value.
range_t range = br->range_;
if (br->bits_ < 0) {
VP8LoadNewBytes(br);
}
{
const int pos = br->bits_;
const range_t split = (range * prob) >> 8;
const range_t value = (range_t)(br->value_ >> pos);
const int bit = (value > split);
if (bit) {
range -= split;
br->value_ -= (bit_t)(split + 1) << pos;
} else {
range = split + 1;
}
{
const int shift = 7 ^ BitsLog2Floor(range);
range <<= shift;
br->bits_ -= shift;
}
br->range_ = range - 1;
BT_TRACK(br);
return bit;
}
}
// simplified version of VP8GetBit() for prob=0x80 (note shift is always 1 here)
static WEBP_UBSAN_IGNORE_UNSIGNED_OVERFLOW WEBP_INLINE
int VP8GetSigned(VP8BitReader* WEBP_RESTRICT const br, int v,
const char label[]) {
if (br->bits_ < 0) {
VP8LoadNewBytes(br);
}
{
const int pos = br->bits_;
const range_t split = br->range_ >> 1;
const range_t value = (range_t)(br->value_ >> pos);
const int32_t mask = (int32_t)(split - value) >> 31; // -1 or 0
br->bits_ -= 1;
br->range_ += (range_t)mask;
br->range_ |= 1;
br->value_ -= (bit_t)((split + 1) & (uint32_t)mask) << pos;
BT_TRACK(br);
return (v ^ mask) - mask;
}
}
static WEBP_INLINE int VP8GetBitAlt(VP8BitReader* WEBP_RESTRICT const br,
int prob, const char label[]) {
// Don't move this declaration! It makes a big speed difference to store
// 'range' *before* calling VP8LoadNewBytes(), even if this function doesn't
// alter br->range_ value.
range_t range = br->range_;
if (br->bits_ < 0) {
VP8LoadNewBytes(br);
}
{
const int pos = br->bits_;
const range_t split = (range * prob) >> 8;
const range_t value = (range_t)(br->value_ >> pos);
int bit; // Don't use 'const int bit = (value > split);", it's slower.
if (value > split) {
range -= split + 1;
br->value_ -= (bit_t)(split + 1) << pos;
bit = 1;
} else {
range = split;
bit = 0;
}
if (range <= (range_t)0x7e) {
const int shift = kVP8Log2Range[range];
range = kVP8NewRange[range];
br->bits_ -= shift;
}
br->range_ = range;
BT_TRACK(br);
return bit;
}
}
#ifdef __cplusplus
} // extern "C"
#endif
#endif // WEBP_UTILS_BIT_READER_INL_UTILS_H_