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<?php
/*
* Copyright 2007 ZXing authors
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
namespace Zxing\Common;
/**
* <p>This provides an easy abstraction to read bits at a time from a sequence of bytes, where the
* number of bits read is not often a multiple of 8.</p>
*
* <p>This class is thread-safe but not reentrant -- unless the caller modifies the bytes array
* it passed in, in which case all bets are off.</p>
*
* @author Sean Owen
*/
final class BitSource
{
private int $byteOffset = 0;
private int $bitOffset = 0;
/**
* @param array $bytes bytes from which this will read bits. Bits will be read from the first byte first.
* Bits are read within a byte from most-significant to least-significant bit.
*/
public function __construct(private array $bytes)
{
}
/**
* @return int of next bit in current byte which would be read by the next call to {@link #readBits(int)}.
*/
public function getBitOffset(): int
{
return $this->bitOffset;
}
/**
* @return int of next byte in input byte array which would be read by the next call to {@link #readBits(int)}.
*/
public function getByteOffset(): int
{
return $this->byteOffset;
}
/**
* @param int $numBits number of bits to read
*
* @return int representing the bits read. The bits will appear as the least-significant
* bits of the int
* @throws \InvalidArgumentException if numBits isn't in [1,32] or more than is available
*/
public function readBits($numBits)
{
if ($numBits < 1 || $numBits > 32 || $numBits > $this->available()) {
throw new \InvalidArgumentException(strval($numBits));
}
$result = 0;
// First, read remainder from current byte
if ($this->bitOffset > 0) {
$bitsLeft = 8 - $this->bitOffset;
$toRead = $numBits < $bitsLeft ? $numBits : $bitsLeft;
$bitsToNotRead = $bitsLeft - $toRead;
$mask = (0xFF >> (8 - $toRead)) << $bitsToNotRead;
$result = ($this->bytes[$this->byteOffset] & $mask) >> $bitsToNotRead;
$numBits -= $toRead;
$this->bitOffset += $toRead;
if ($this->bitOffset == 8) {
$this->bitOffset = 0;
$this->byteOffset++;
}
}
// Next read whole bytes
if ($numBits > 0) {
while ($numBits >= 8) {
$result = ($result << 8) | ($this->bytes[$this->byteOffset] & 0xFF);
$this->byteOffset++;
$numBits -= 8;
}
// Finally read a partial byte
if ($numBits > 0) {
$bitsToNotRead = 8 - $numBits;
$mask = (0xFF >> $bitsToNotRead) << $bitsToNotRead;
$result = ($result << $numBits) | (($this->bytes[$this->byteOffset] & $mask) >> $bitsToNotRead);
$this->bitOffset += $numBits;
}
}
return $result;
}
/**
* @return int of bits that can be read successfully
*/
public function available(): int
{
return 8 * ((is_countable($this->bytes) ? count($this->bytes) : 0) - $this->byteOffset) - $this->bitOffset;
}
}
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