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77 lines (63 loc) · 1.71 KB
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/*
* Copyright 2016 Nu-book Inc.
* Copyright 2016 ZXing authors
*/
// SPDX-License-Identifier: Apache-2.0
#include "BitSource.h"
#include "ByteArray.h"
#include "ZXAlgorithms.h"
#include <stdexcept>
namespace ZXing {
int
BitSource::available() const
{
return 8 * (Size(_bytes) - _byteOffset) - _bitOffset;
}
static int ReadBitsImpl(int numBits, const ByteArray& _bytes, int available, int& _byteOffset, int& _bitOffset)
{
if (numBits < 1 || numBits > 32 || numBits > available) {
throw std::out_of_range("BitSource::readBits: out of range");
}
int result = 0;
// First, read remainder from current byte
if (_bitOffset > 0) {
int bitsLeft = 8 - _bitOffset;
int toRead = numBits < bitsLeft ? numBits : bitsLeft;
int bitsToNotRead = bitsLeft - toRead;
int mask = (0xFF >> (8 - toRead)) << bitsToNotRead;
result = (_bytes[_byteOffset] & mask) >> bitsToNotRead;
numBits -= toRead;
_bitOffset += toRead;
if (_bitOffset == 8) {
_bitOffset = 0;
_byteOffset++;
}
}
// Next read whole bytes
if (numBits > 0) {
while (numBits >= 8) {
result = (result << 8) | _bytes[_byteOffset];
_byteOffset++;
numBits -= 8;
}
// Finally read a partial byte
if (numBits > 0) {
int bitsToNotRead = 8 - numBits;
int mask = (0xFF >> bitsToNotRead) << bitsToNotRead;
result = (result << numBits) | ((_bytes[_byteOffset] & mask) >> bitsToNotRead);
_bitOffset += numBits;
}
}
return result;
}
int BitSource::readBits(int numBits)
{
return ReadBitsImpl(numBits, _bytes, available(), _byteOffset, _bitOffset);
}
int BitSource::peakBits(int numBits) const
{
int bitOffset = _bitOffset;
int byteOffset = _byteOffset;
return ReadBitsImpl(numBits, _bytes, available(), byteOffset, bitOffset);
}
} // ZXing