ParagonIE_Sodium_Core32_Int64::mulInt64

    public function mulInt64(ParagonIE_Sodium_Core32_Int64 $int, $size = 0)
    {
        if (ParagonIE_Sodium_Compat::$fastMult) {
            return $this->mulInt64Fast($int);
        }
        ParagonIE_Sodium_Core32_Util::declareScalarType($size, 'int', 2);
        if (!$size) {
            $size = 63;
        }
        list($a, $b) = self::ctSelect($this, $int);

        $return = new ParagonIE_Sodium_Core32_Int64();
        $return->unsignedInt = $this->unsignedInt;

        // Initialize:
        $ret0 = 0;
        $ret1 = 0;
        $ret2 = 0;
        $ret3 = 0;
        $a0 = $a->limbs[0];
        $a1 = $a->limbs[1];
        $a2 = $a->limbs[2];
        $a3 = $a->limbs[3];
        $b0 = $b->limbs[0];
        $b1 = $b->limbs[1];
        $b2 = $b->limbs[2];
        $b3 = $b->limbs[3];

        /** @var int $size */
        /** @var int $i */
        for ($i = (int) $size; $i >= 0; --$i) {
            $mask = -($b3 & 1);
            $x0 = $a0 & $mask;
            $x1 = $a1 & $mask;
            $x2 = $a2 & $mask;
            $x3 = $a3 & $mask;

            $ret3 += $x3;
            $c = $ret3 >> 16;

            $ret2 += $x2 + $c;
            $c = $ret2 >> 16;

            $ret1 += $x1 + $c;
            $c = $ret1 >> 16;

            $ret0 += $x0 + $c;

            $ret0 &= 0xffff;
            $ret1 &= 0xffff;
            $ret2 &= 0xffff;
            $ret3 &= 0xffff;

            $a3 = $a3 << 1;
            $x3 = $a3 >> 16;
            $a2 = ($a2 << 1) | $x3;
            $x2 = $a2 >> 16;
            $a1 = ($a1 << 1) | $x2;
            $x1 = $a1 >> 16;
            $a0 = ($a0 << 1) | $x1;
            $a0 &= 0xffff;
            $a1 &= 0xffff;
            $a2 &= 0xffff;
            $a3 &= 0xffff;

            $x0 = ($b0 & 1) << 16;
            $x1 = ($b1 & 1) << 16;
            $x2 = ($b2 & 1) << 16;

            $b0 = ($b0 >> 1);
            $b1 = (($b1 | $x0) >> 1);
            $b2 = (($b2 | $x1) >> 1);
            $b3 = (($b3 | $x2) >> 1);

            $b0 &= 0xffff;
            $b1 &= 0xffff;
            $b2 &= 0xffff;
            $b3 &= 0xffff;

        }
        $return->limbs[0] = $ret0;
        $return->limbs[1] = $ret1;
        $return->limbs[2] = $ret2;
        $return->limbs[3] = $ret3;

        return $return;
    }