ParagonIE_Sodium_Core32_Int64::mulIntFast

    public function mulIntFast($int)
    {
        // Handle negative numbers
        $aNeg = ($this->limbs[0] >> 15) & 1;
        $bNeg = ($int >> 31) & 1;
        $a = array_reverse($this->limbs);
        $b = array(
            $int & 0xffff,
            ($int >> 16) & 0xffff,
            -$bNeg & 0xffff,
            -$bNeg & 0xffff
        );
        if ($aNeg) {
            for ($i = 0; $i < 4; ++$i) {
                $a[$i] = ($a[$i] ^ 0xffff) & 0xffff;
            }
            ++$a[0];
        }
        if ($bNeg) {
            for ($i = 0; $i < 4; ++$i) {
                $b[$i] = ($b[$i] ^ 0xffff) & 0xffff;
            }
            ++$b[0];
        }
        // Multiply
        $res = $this->multiplyLong($a, $b);

        // Re-apply negation to results
        if ($aNeg !== $bNeg) {
            for ($i = 0; $i < 4; ++$i) {
                $res[$i] = (0xffff ^ $res[$i]) & 0xffff;
            }
            // Handle integer overflow
            $c = 1;
            for ($i = 0; $i < 4; ++$i) {
                $res[$i] += $c;
                $c = $res[$i] >> 16;
                $res[$i] &= 0xffff;
            }
        }

        // Return our values
        $return = new ParagonIE_Sodium_Core32_Int64();
        $return->limbs = array(
            $res[3] & 0xffff,
            $res[2] & 0xffff,
            $res[1] & 0xffff,
            $res[0] & 0xffff
        );
        if (count($res) > 4) {
            $return->overflow = $res[4] & 0xffff;
        }
        $return->unsignedInt = $this->unsignedInt;
        return $return;
    }