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