ParagonIE_Sodium_Core_Ristretto255::ristretto255_point_is_canonical( string $s ): int

123    public static function ristretto255_point_is_canonical($s)124    {125        $c = (self::chrToInt($s[31]) & 0x7f) ^ 0x7f;126        for ($i = 30; $i > 0; --$i) {127            $c |= self::chrToInt($s[$i]) ^ 0xff;128        }129        $c = ($c - 1) >> 8;130        $d = (0xed - 1 - self::chrToInt($s[0])) >> 8;131        $e = self::chrToInt($s[31]) >> 7;132 133        return 1 - ((($c & $d) | $e | self::chrToInt($s[0])) & 1);134    }