78 lines
1.7 KiB
C++
78 lines
1.7 KiB
C++
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/*
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* Copyright 2016 Nu-book Inc.
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* Copyright 2016 ZXing authors
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*/
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// SPDX-License-Identifier: Apache-2.0
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#include "BitSource.h"
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#include "ByteArray.h"
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#include "ZXAlgorithms.h"
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#include <stdexcept>
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namespace ZXing {
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int
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BitSource::available() const
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{
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return 8 * (Size(_bytes) - _byteOffset) - _bitOffset;
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}
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static int ReadBitsImpl(int numBits, const ByteArray& _bytes, int available, int& _byteOffset, int& _bitOffset)
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{
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if (numBits < 1 || numBits > 32 || numBits > available) {
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throw std::out_of_range("BitSource::readBits: out of range");
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}
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int result = 0;
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// First, read remainder from current byte
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if (_bitOffset > 0) {
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int bitsLeft = 8 - _bitOffset;
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int toRead = numBits < bitsLeft ? numBits : bitsLeft;
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int bitsToNotRead = bitsLeft - toRead;
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int mask = (0xFF >> (8 - toRead)) << bitsToNotRead;
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result = (_bytes[_byteOffset] & mask) >> bitsToNotRead;
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numBits -= toRead;
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_bitOffset += toRead;
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if (_bitOffset == 8) {
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_bitOffset = 0;
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_byteOffset++;
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}
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}
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// Next read whole bytes
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if (numBits > 0) {
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while (numBits >= 8) {
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result = (result << 8) | _bytes[_byteOffset];
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_byteOffset++;
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numBits -= 8;
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}
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// Finally read a partial byte
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if (numBits > 0) {
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int bitsToNotRead = 8 - numBits;
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int mask = (0xFF >> bitsToNotRead) << bitsToNotRead;
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result = (result << numBits) | ((_bytes[_byteOffset] & mask) >> bitsToNotRead);
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_bitOffset += numBits;
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}
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}
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return result;
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}
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int BitSource::readBits(int numBits)
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{
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return ReadBitsImpl(numBits, _bytes, available(), _byteOffset, _bitOffset);
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}
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int BitSource::peakBits(int numBits) const
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{
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int bitOffset = _bitOffset;
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int byteOffset = _byteOffset;
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return ReadBitsImpl(numBits, _bytes, available(), byteOffset, bitOffset);
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}
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} // ZXing
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