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perf: simplify counter packing and dynamic truncation in generateOTP #284

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perf: simplify counter packing and dynamic truncation in generateOTP #284

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43fb9c2
perf: simplify counter packing and dynamic truncation in generateOTP
pataar Jun 10, 2026
2c0570a
style: import ord function per ECS rules
pataar Jun 10, 2026
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26 changes: 7 additions & 19 deletions src/OTP.php
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Original file line number Diff line number Diff line change
Expand Up @@ -5,12 +5,12 @@
namespace OTPHP;

use function array_key_exists;
use function chr;
use function count;
use Exception;
use function in_array;
use function is_int;
use function is_string;
use function ord;
use OTPHP\Exception\InvalidLabelException;
use OTPHP\Exception\InvalidParameterException;
use OTPHP\Exception\ParameterNotFoundException;
Expand Down Expand Up @@ -287,14 +287,13 @@ final protected static function generateSecret(?int $secretSize = null): string
*/
protected function generateOTP(int $input): string
{
$hash = hash_hmac($this->getDigest(), $this->intToByteString($input), $this->getDecodedSecret(), true);
$unpacked = unpack('C*', $hash);
$unpacked !== false || throw new InvalidParameterException('Invalid data.', 'hash', $hash);
/** @var list<int> $hmac */
$hmac = array_values($unpacked);
$hash = hash_hmac($this->getDigest(), pack('J', $input), $this->getDecodedSecret(), true);

$offset = ($hmac[count($hmac) - 1] & 0xF);
$code = ($hmac[$offset] & 0x7F) << 24 | ($hmac[$offset + 1] & 0xFF) << 16 | ($hmac[$offset + 2] & 0xFF) << 8 | ($hmac[$offset + 3] & 0xFF);
$offset = ord($hash[strlen($hash) - 1]) & 0xF;
$code = (ord($hash[$offset]) & 0x7F) << 24
| (ord($hash[$offset + 1]) & 0xFF) << 16
| (ord($hash[$offset + 2]) & 0xFF) << 8
| (ord($hash[$offset + 3]) & 0xFF);
$otp = $code % (10 ** $this->getDigits());

return str_pad((string) $otp, $this->getDigits(), '0', STR_PAD_LEFT);
Expand Down Expand Up @@ -414,17 +413,6 @@ private function getDecodedSecret(): string
return $decoded;
}

private function intToByteString(int $int): string
{
$result = [];
while ($int !== 0) {
$result[] = chr($int & 0xFF);
$int >>= 8;
}

return str_pad(implode('', array_reverse($result)), 8, "\000", STR_PAD_LEFT);
}

/**
* @return non-empty-string
*/
Expand Down