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