\Zxing\Qrcode\DecoderFormatInformation

<?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\Qrcode\Decoder;

/**
 * <p>Encapsulates a QR Code's format information, including the data mask used and
 * error correction level.</p>
 *
 * @author Sean Owen
 * @see    DataMask
 * @see    ErrorCorrectionLevel
 */
final class FormatInformation
{
    public static $FORMAT_INFO_MASK_QR;

    /**
     * See ISO 18004:2006, Annex C, Table C.1
     */
    public static $FORMAT_INFO_DECODE_LOOKUP;
    /**
     * Offset i holds the number of 1 bits in the binary representation of i
     */
    private static $BITS_SET_IN_HALF_BYTE;

    private $errorCorrectionLevel;
    private $dataMask;

    private function __construct($formatInfo)
    {
        // Bits 3,4
        $this->errorCorrectionLevel = ErrorCorrectionLevel::forBits(($formatInfo >> 3) & 0x03);
        // Bottom 3 bits
        $this->dataMask = ($formatInfo & 0x07);//(byte)
    }

    public static function Init()
    {
        self::$FORMAT_INFO_MASK_QR       = 0x5412;
        self::$BITS_SET_IN_HALF_BYTE     = [0, 1, 1, 2, 1, 2, 2, 3, 1, 2, 2, 3, 2, 3, 3, 4];
        self::$FORMAT_INFO_DECODE_LOOKUP = [
            [0x5412, 0x00],
            [0x5125, 0x01],
            [0x5E7C, 0x02],
            [0x5B4B, 0x03],
            [0x45F9, 0x04],
            [0x40CE, 0x05],
            [0x4F97, 0x06],
            [0x4AA0, 0x07],
            [0x77C4, 0x08],
            [0x72F3, 0x09],
            [0x7DAA, 0x0A],
            [0x789D, 0x0B],
            [0x662F, 0x0C],
            [0x6318, 0x0D],
            [0x6C41, 0x0E],
            [0x6976, 0x0F],
            [0x1689, 0x10],
            [0x13BE, 0x11],
            [0x1CE7, 0x12],
            [0x19D0, 0x13],
            [0x0762, 0x14],
            [0x0255, 0x15],
            [0x0D0C, 0x16],
            [0x083B, 0x17],
            [0x355F, 0x18],
            [0x3068, 0x19],
            [0x3F31, 0x1A],
            [0x3A06, 0x1B],
            [0x24B4, 0x1C],
            [0x2183, 0x1D],
            [0x2EDA, 0x1E],
            [0x2BED, 0x1F],
        ];
    }

    /**
     * @param maskedFormatInfo1 ; format info indicator, with mask still applied
     * @param maskedFormatInfo2 ; second copy of same info; both are checked at the same time
     *                          to establish best match
     *
     * @return information about the format it specifies, or {@code null}
     *  if doesn't seem to match any known pattern
     */
    public static function decodeFormatInformation($maskedFormatInfo1, $maskedFormatInfo2)
    {
        $formatInfo = self::doDecodeFormatInformation($maskedFormatInfo1, $maskedFormatInfo2);
        if ($formatInfo != null) {
            return $formatInfo;
        }
        // Should return null, but, some QR codes apparently
        // do not mask this info. Try again by actually masking the pattern
        // first
        return self::doDecodeFormatInformation($maskedFormatInfo1 ^ self::$FORMAT_INFO_MASK_QR,
            $maskedFormatInfo2 ^ self::$FORMAT_INFO_MASK_QR);
    }

    private static function doDecodeFormatInformation($maskedFormatInfo1, $maskedFormatInfo2)
    {
        // Find the int in FORMAT_INFO_DECODE_LOOKUP with fewest bits differing
        $bestDifference = PHP_INT_MAX;
        $bestFormatInfo = 0;
        foreach (self::$FORMAT_INFO_DECODE_LOOKUP as $decodeInfo) {
            $targetInfo = $decodeInfo[0];
            if ($targetInfo == $maskedFormatInfo1 || $targetInfo == $maskedFormatInfo2) {
                // Found an exact match
                return new FormatInformation($decodeInfo[1]);
            }
            $bitsDifference = self::numBitsDiffering($maskedFormatInfo1, $targetInfo);
            if ($bitsDifference < $bestDifference) {
                $bestFormatInfo = $decodeInfo[1];
                $bestDifference = $bitsDifference;
            }
            if ($maskedFormatInfo1 != $maskedFormatInfo2) {
                // also try the other option
                $bitsDifference = self::numBitsDiffering($maskedFormatInfo2, $targetInfo);
                if ($bitsDifference < $bestDifference) {
                    $bestFormatInfo = $decodeInfo[1];
                    $bestDifference = $bitsDifference;
                }
            }
        }
        // Hamming distance of the 32 masked codes is 7, by construction, so <= 3 bits
        // differing means we found a match
        if ($bestDifference <= 3) {
            return new FormatInformation($bestFormatInfo);
        }

        return null;
    }

    public static function numBitsDiffering($a, $b)
    {
        $a ^= $b; // a now has a 1 bit exactly where its bit differs with b's
        // Count bits set quickly with a series of lookups:
        return self::$BITS_SET_IN_HALF_BYTE[$a & 0x0F] +
            self::$BITS_SET_IN_HALF_BYTE[(int)(uRShift($a, 4) & 0x0F)] +
            self::$BITS_SET_IN_HALF_BYTE[(uRShift($a, 8) & 0x0F)] +
            self::$BITS_SET_IN_HALF_BYTE[(uRShift($a, 12) & 0x0F)] +
            self::$BITS_SET_IN_HALF_BYTE[(uRShift($a, 16) & 0x0F)] +
            self::$BITS_SET_IN_HALF_BYTE[(uRShift($a, 20) & 0x0F)] +
            self::$BITS_SET_IN_HALF_BYTE[(uRShift($a, 24) & 0x0F)] +
            self::$BITS_SET_IN_HALF_BYTE[(uRShift($a, 28) & 0x0F)];
    }

    public function getErrorCorrectionLevel()
    {
        return $this->errorCorrectionLevel;
    }

    public function getDataMask()
    {
        return $this->dataMask;
    }

    //@Override
    public function hashCode()
    {
        return ($this->errorCorrectionLevel->ordinal() << 3) | (int)($this->dataMask);
    }

    //@Override
    public function equals($o)
    {
        if (!($o instanceof FormatInformation)) {
            return false;
        }
        $other = $o;

        return $this->errorCorrectionLevel == $other->errorCorrectionLevel &&
            $this->dataMask == $other->dataMask;
    }
}

FormatInformation::Init();