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<?php |
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declare(strict_types=1); |
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namespace Afonso\Base24; |
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/** |
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* An encoder/decoder that uses the Base 24 binary-to-text encoding scheme. |
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*/ |
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class Encoder |
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{ |
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/** |
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* The alphabet used by this encoder. |
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* |
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* @var string |
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*/ |
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const ALPHABET = 'ZAC2B3EF4GH5TK67P8RS9WXY'; |
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/** |
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* The length of the alphabet used by this encoder. |
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* |
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* @var int |
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*/ |
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const ALPHABET_LENGTH = 24; |
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private $encodeMap = []; |
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private $decodeMap = []; |
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public function __construct() |
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{ |
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105 |
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for ($i = 0; $i < strlen(self::ALPHABET); $i++) { |
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$this->decodeMap[self::ALPHABET[$i]] = $i; |
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$this->decodeMap[strtolower(self::ALPHABET[$i])] = $i; |
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$this->encodeMap[$i] = self::ALPHABET[$i]; |
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} |
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} |
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/** |
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* Convert the given array of bytes into a Base 24-encoded string. |
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* |
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* The length of the input array must be a multiple of 4, otherwise this |
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* method will throw an exception. |
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* |
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* @param int[] $input |
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* @return string |
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* @throws \InvalidArgumentException |
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*/ |
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public function encode(array $input): string |
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{ |
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$dataLength = count($input); |
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if ($dataLength % 4 !== 0) { |
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throw new \InvalidArgumentException('Input to encode must have a length multiple of 4'); |
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} |
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$result = ''; |
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for ($i = 0; $i < $dataLength / 4; $i++) { |
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$j = $i * 4; |
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$mask = 0xFF; |
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$b3 = $input[$j] & $mask; |
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$b2 = $input[$j + 1] & $mask; |
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$b1 = $input[$j + 2] & $mask; |
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$b0 = $input[$j + 3] & $mask; |
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$value = 0xFFFFFFFF & |
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(($b3 << 24) | ($b2 << 16) | ($b1 << 8) | $b0); |
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$subResult = ''; |
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for ($k = 0; $k < 7; $k++) { |
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$idx = $value % 24; |
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$value = $value / self::ALPHABET_LENGTH; |
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$subResult = $this->encodeMap[$idx] . $subResult; |
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} |
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$result .= $subResult; |
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} |
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return $result; |
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} |
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/** |
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* Convert the given Base 24-encoded string into an array of bytes. |
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* |
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* The length of the input string must be a multiple of 7, otherwise this |
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* method will throw an exception. |
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* |
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* @param string $input |
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* @return int[] |
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* @throws \InvalidArgumentException |
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*/ |
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public function decode(string $input): array |
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{ |
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$dataLength = strlen($input); |
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if ($dataLength % 7 !== 0) { |
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throw new \InvalidArgumentException('Input to decode must have a length multiple of 7'); |
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} |
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$bytes = []; |
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for ($i = 0; $i < $dataLength / 7; $i++) { |
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$j = $i * 7; |
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$subData = substr($input, $j, 7); |
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$value = 0; |
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foreach (str_split($subData) as $s) { |
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if (array_key_exists($s, $this->decodeMap) === false) { |
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throw new \InvalidArgumentException('Input to decode contains an invalid character'); |
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} |
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$idx = $this->decodeMap[$s]; |
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$value = self::ALPHABET_LENGTH * $value + $idx; |
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} |
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$mask = 0xFF; |
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$b0 = ($value & ($mask << 24)) >> 24; |
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$b1 = ($value & ($mask << 16)) >> 16; |
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$b2 = ($value & ($mask << 8)) >> 8; |
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$b3 = $value & $mask; |
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$bytes[] = $b0; |
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$bytes[] = $b1; |
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$bytes[] = $b2; |
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$bytes[] = $b3; |
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} |
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return $bytes; |
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} |
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} |
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carlosafonso /
php-base24
