ParagonIE_Sodium_Core32_Int32::mulInt32

    public function mulInt32(ParagonIE_Sodium_Core32_Int32 $int, $size = 0)
    {
        ParagonIE_Sodium_Core32_Util::declareScalarType($size, 'int', 2);
        if (ParagonIE_Sodium_Compat::$fastMult) {
            return $this->mulInt32Fast($int);
        }
        if (!$size) {
            $size = 31;
        }
        /** @var int $size */

        $a = clone $this;
        $b = clone $int;
        $return = new ParagonIE_Sodium_Core32_Int32();
        $return->unsignedInt = $this->unsignedInt;

        // Initialize:
        $ret0 = 0;
        $ret1 = 0;
        $a0 = $a->limbs[0];
        $a1 = $a->limbs[1];
        $b0 = $b->limbs[0];
        $b1 = $b->limbs[1];

        /** @var int $size */
        /** @var int $i */
        for ($i = $size; $i >= 0; --$i) {
            $m = (int) (-($b1 & 1));
            $x0 = $a0 & $m;
            $x1 = $a1 & $m;

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

            $ret0 += $x0 + $c;

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

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

            $x0 = ($b0 & 1) << 16;
            $b0 = ($b0 >> 1);
            $b1 = (($b1 | $x0) >> 1);

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

        }
        $return->limbs[0] = $ret0;
        $return->limbs[1] = $ret1;

        return $return;
    }