2014-02-10 01:10:30 +00:00
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// Copyright 2010 Google Inc. All Rights Reserved.
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//
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2014-02-11 01:37:07 +00:00
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// This code is licensed under the same terms as WebM:
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// Software License Agreement: http://www.webmproject.org/license/software/
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// Additional IP Rights Grant: http://www.webmproject.org/license/additional/
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2014-02-10 01:10:30 +00:00
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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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2014-02-10 01:10:30 +00:00
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#include "../webp/types.h"
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2014-02-11 01:37:07 +00:00
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#if defined(__cplusplus) || defined(c_plusplus)
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2014-02-10 01:10:30 +00:00
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extern "C" {
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#endif
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2014-02-11 01:37:07 +00:00
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#define BITS 32 // can be 32, 16 or 8
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#define MASK ((((bit_t)1) << (BITS)) - 1)
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#if (BITS == 32)
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typedef uint64_t bit_t; // natural register type
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typedef uint32_t lbit_t; // natural type for memory I/O
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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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//------------------------------------------------------------------------------
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// Bitreader and code-tree reader
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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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bit_t range_; // current range minus 1. In [127, 254] interval.
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bit_t value_; // current value
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int missing_; // number of missing bits in value_ (8bit)
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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 bit_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 && br->buf_);
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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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#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; // 32b -> 64b zero-extension
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#elif defined(_MSC_VER)
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bits = _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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#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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#endif
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#else // LITTLE_ENDIAN
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bits = (bit_t)in_bits;
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#endif
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br->value_ |= bits << br->missing_;
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br->missing_ -= (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, bit_t split) {
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const bit_t value_split = split | (MASK);
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if (br->missing_ > 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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if (br->value_ > value_split) {
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br->range_ -= value_split + 1;
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br->value_ -= value_split + 1;
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return 1;
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} else {
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br->range_ = value_split;
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return 0;
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}
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}
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static WEBP_INLINE void VP8Shift(VP8BitReader* const br) {
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// range_ is in [0..127] interval here.
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const int 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->missing_ += shift;
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}
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static WEBP_INLINE int VP8GetBit(VP8BitReader* const br, int prob) {
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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 bit_t split =
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(bit_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_ <= (((bit_t)0x7e << (BITS)) | (MASK))) {
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VP8Shift(br);
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}
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return bit;
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}
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static WEBP_INLINE int VP8GetSigned(VP8BitReader* const br, int v) {
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const bit_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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2014-02-11 01:37:07 +00:00
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// -----------------------------------------------------------------------------
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// Bitreader
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2014-02-10 01:10:30 +00:00
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typedef struct {
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uint64_t val_;
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const uint8_t* buf_;
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size_t len_;
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size_t pos_;
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int bit_pos_;
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int eos_;
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int error_;
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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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// Reads one bit from Read Buffer. Flags an error in case end_of_stream.
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// Flags eos after reading last bit from the buffer.
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uint32_t VP8LReadOneBit(VP8LBitReader* const br);
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// VP8LReadOneBitUnsafe is faster than VP8LReadOneBit, but it can be called only
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// 32 times after the last VP8LFillBitWindow. Any subsequent calls
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// (without VP8LFillBitWindow) will return invalid data.
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static WEBP_INLINE uint32_t VP8LReadOneBitUnsafe(VP8LBitReader* const br) {
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const uint32_t val = (br->val_ >> br->bit_pos_) & 1;
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++br->bit_pos_;
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return val;
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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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2014-02-11 01:37:07 +00:00
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#if defined(__cplusplus) || defined(c_plusplus)
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2014-02-10 01:10:30 +00:00
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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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