diff --git a/src/Data/AlphaNum.php b/src/Data/AlphaNum.php
index 882c1f7ea..5bcd0ce0e 100644
--- a/src/Data/AlphaNum.php
+++ b/src/Data/AlphaNum.php
@@ -12,7 +12,7 @@
 namespace chillerlan\QRCode\Data;
 
 use chillerlan\QRCode\Common\{BitBuffer, Mode};
-use function ceil, intdiv, str_split;
+use function ceil, intdiv, preg_match, strpos;
 
 /**
  * Alphanumeric mode: 0 to 9, A to Z, space, $ % * + - . / :
@@ -25,30 +25,9 @@ final class AlphaNum extends QRDataModeAbstract{
 	/**
 	 * ISO/IEC 18004:2000 Table 5
 	 *
-	 * @var int[]
+	 * @var string
 	 */
-	private const CHAR_TO_ORD = [
-		// phpcs:ignore
-		'0' =>  0, '1' =>  1, '2' =>  2, '3' =>  3, '4' =>  4, '5' =>  5, '6' =>  6, '7' =>  7,
-		// phpcs:ignore
-		'8' =>  8, '9' =>  9, 'A' => 10, 'B' => 11, 'C' => 12, 'D' => 13, 'E' => 14, 'F' => 15,
-		'G' => 16, 'H' => 17, 'I' => 18, 'J' => 19, 'K' => 20, 'L' => 21, 'M' => 22, 'N' => 23,
-		'O' => 24, 'P' => 25, 'Q' => 26, 'R' => 27, 'S' => 28, 'T' => 29, 'U' => 30, 'V' => 31,
-		'W' => 32, 'X' => 33, 'Y' => 34, 'Z' => 35, ' ' => 36, '$' => 37, '%' => 38, '*' => 39,
-		'+' => 40, '-' => 41, '.' => 42, '/' => 43, ':' => 44,
-	];
-
-	/**
-	 * @var string[]
-	 */
-	private const ORD_TO_CHAR = [
-		'0', '1', '2', '3', '4', '5', '6', '7',
-		'8', '9', 'A', 'B', 'C', 'D', 'E', 'F',
-		'G', 'H', 'I', 'J', 'K', 'L', 'M', 'N',
-		'O', 'P', 'Q', 'R', 'S', 'T', 'U', 'V',
-		'W', 'X', 'Y', 'Z', ' ', '$', '%', '*',
-		'+', '-', '.', '/', ':',
-	];
+	private const CHAR_MAP = '0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ $%*+-./:';
 
 	public const DATAMODE = Mode::ALPHANUM;
 
@@ -57,18 +36,7 @@ public function getLengthInBits():int{
 	}
 
 	public static function validateString(string $string):bool{
-
-		if($string === ''){
-			return false;
-		}
-
-		foreach(str_split($string) as $chr){
-			if(!isset(self::CHAR_TO_ORD[$chr])){
-				return false;
-			}
-		}
-
-		return true;
+		return (bool)preg_match('#^['.self::CHAR_MAP.']+$#', $string);
 	}
 
 	public function write(BitBuffer $bitBuffer, int $versionNumber):static{
@@ -82,14 +50,14 @@ public function write(BitBuffer $bitBuffer, int $versionNumber):static{
 		// encode 2 characters in 11 bits
 		for($i = 0; ($i + 1) < $len; $i += 2){
 			$bitBuffer->put(
-				(self::CHAR_TO_ORD[$this->data[$i]] * 45 + self::CHAR_TO_ORD[$this->data[($i + 1)]]),
+				($this->ord($this->data[$i]) * 45 + $this->ord($this->data[($i + 1)])),
 				11,
 			);
 		}
 
 		// encode a remaining character in 6 bits
 		if($i < $len){
-			$bitBuffer->put(self::CHAR_TO_ORD[$this->data[$i]], 6);
+			$bitBuffer->put($this->ord($this->data[$i]), 6);
 		}
 
 		return $this;
@@ -111,8 +79,8 @@ public static function decodeSegment(BitBuffer $bitBuffer, int $versionNumber):s
 			}
 
 			$nextTwoCharsBits  = $bitBuffer->read(11);
-			$result           .= self::ORD_TO_CHAR[intdiv($nextTwoCharsBits, 45)];
-			$result           .= self::ORD_TO_CHAR[($nextTwoCharsBits % 45)];
+			$result           .= self::chr(intdiv($nextTwoCharsBits, 45));
+			$result           .= self::chr($nextTwoCharsBits % 45);
 			$length           -= 2;
 		}
 
@@ -122,10 +90,35 @@ public static function decodeSegment(BitBuffer $bitBuffer, int $versionNumber):s
 				throw new QRCodeDataException('not enough bits available'); // @codeCoverageIgnore
 			}
 
-			$result .= self::ORD_TO_CHAR[$bitBuffer->read(6)];
+			$result .= self::chr($bitBuffer->read(6));
 		}
 
 		return $result;
 	}
 
+	/**
+	 * @throws \chillerlan\QRCode\Data\QRCodeDataException
+	 */
+	private function ord(string $chr):int{
+		$ord = strpos(self::CHAR_MAP, $chr);
+
+		if($ord === false){
+			throw new QRCodeDataException('invalid character'); // @codeCoverageIgnore
+		}
+
+		return $ord;
+	}
+
+	/**
+	 * @throws \chillerlan\QRCode\Data\QRCodeDataException
+	 */
+	private static function chr(int $ord):string{
+
+		if($ord < 0 || $ord > 44){
+			throw new QRCodeDataException('invalid character code'); // @codeCoverageIgnore
+		}
+
+		return self::CHAR_MAP[$ord];
+	}
+
 }
diff --git a/src/Data/Number.php b/src/Data/Number.php
index a776bbd73..2830fc2e7 100644
--- a/src/Data/Number.php
+++ b/src/Data/Number.php
@@ -12,7 +12,7 @@
 namespace chillerlan\QRCode\Data;
 
 use chillerlan\QRCode\Common\{BitBuffer, Mode};
-use function ceil, intdiv, str_split, substr, unpack;
+use function ceil, intdiv, preg_match, substr, unpack;
 
 /**
  * Numeric mode: decimal digits 0 to 9
@@ -22,20 +22,6 @@
  */
 final class Number extends QRDataModeAbstract{
 
-	/**
-	 * @var int[]
-	 */
-	private const NUMBER_TO_ORD = [
-		'0' => 0, '1' => 1, '2' => 2, '3' => 3, '4' => 4, '5' => 5, '6' => 6, '7' => 7, '8' => 8, '9' => 9,
-	];
-
-	/**
-	 * @var string[]
-	 */
-	private const ORD_TO_NUMBER = [
-		'0', '1', '2', '3', '4', '5', '6', '7', '8', '9',
-	];
-
 	public const DATAMODE = Mode::NUMBER;
 
 	public function getLengthInBits():int{
@@ -43,18 +29,7 @@ public function getLengthInBits():int{
 	}
 
 	public static function validateString(string $string):bool{
-
-		if($string === ''){
-			return false;
-		}
-
-		foreach(str_split($string) as $chr){
-			if(!isset(self::NUMBER_TO_ORD[$chr])){
-				return false;
-			}
-		}
-
-		return true;
+		return (bool)preg_match('/^\d+$/', $string);
 	}
 
 	public function write(BitBuffer $bitBuffer, int $versionNumber):static{
@@ -131,9 +106,9 @@ public static function decodeSegment(BitBuffer $bitBuffer, int $versionNumber):s
 				throw new QRCodeDataException('error decoding numeric value');
 			}
 
-			$result .= self::ORD_TO_NUMBER[intdiv($threeDigitsBits, 100)];
-			$result .= self::ORD_TO_NUMBER[(intdiv($threeDigitsBits, 10) % 10)];
-			$result .= self::ORD_TO_NUMBER[($threeDigitsBits % 10)];
+			$result .= intdiv($threeDigitsBits, 100);
+			$result .= (($threeDigitsBits / 10) % 10);
+			$result .= ($threeDigitsBits % 10);
 
 			$length -= 3;
 		}
@@ -150,8 +125,8 @@ public static function decodeSegment(BitBuffer $bitBuffer, int $versionNumber):s
 				throw new QRCodeDataException('error decoding numeric value');
 			}
 
-			$result .= self::ORD_TO_NUMBER[intdiv($twoDigitsBits, 10)];
-			$result .= self::ORD_TO_NUMBER[($twoDigitsBits % 10)];
+			$result .= intdiv($twoDigitsBits, 10);
+			$result .= ($twoDigitsBits % 10);
 		}
 		elseif($length === 1){
 			// One digit left over to read
@@ -165,7 +140,7 @@ public static function decodeSegment(BitBuffer $bitBuffer, int $versionNumber):s
 				throw new QRCodeDataException('error decoding numeric value');
 			}
 
-			$result .= self::ORD_TO_NUMBER[$digitBits];
+			$result .= $digitBits;
 		}
 
 		return $result;