64 lines
1.5 KiB
PHP
64 lines
1.5 KiB
PHP
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<?php
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namespace FG\ASN1;
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use FG\Utility\BigInteger;
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use InvalidArgumentException;
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/**
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* A base-128 decoder.
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*/
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class Base128
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{
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/**
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* @param int $value
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*
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* @return string
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*/
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public static function encode($value)
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{
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$value = BigInteger::create($value);
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$octets = chr($value->modulus(0x80)->toInteger());
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$value = $value->shiftRight(7);
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while ($value->compare(0) > 0) {
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$octets .= chr(0x80 | $value->modulus(0x80)->toInteger());
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$value = $value->shiftRight(7);
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}
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return strrev($octets);
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}
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/**
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* @param string $octets
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*
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* @throws InvalidArgumentException if the given octets represent a malformed base-128 value or the decoded value would exceed the the maximum integer length
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*
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* @return int
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*/
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public static function decode($octets)
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{
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$bitsPerOctet = 7;
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$value = BigInteger::create(0);
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$i = 0;
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while (true) {
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if (!isset($octets[$i])) {
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throw new InvalidArgumentException(sprintf('Malformed base-128 encoded value (0x%s).', strtoupper(bin2hex($octets)) ?: '0'));
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}
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$octet = ord($octets[$i++]);
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$l1 = $value->shiftLeft($bitsPerOctet);
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$r1 = $octet & 0x7f;
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$value = $l1->add($r1);
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if (0 === ($octet & 0x80)) {
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break;
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}
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}
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return (string)$value;
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}
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}
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