ParagonIE_Sodium_Core32_X25519::crypto_scalarmult_curve25519_ref10

    public static function crypto_scalarmult_curve25519_ref10($n, $p)
    {
        # for (i = 0;i < 32;++i) e[i] = n[i];
        $e = '' . $n;
        # e[0] &= 248;
        $e[0] = self::intToChr(
            self::chrToInt($e[0]) & 248
        );
        # e[31] &= 127;
        # e[31] |= 64;
        $e[31] = self::intToChr(
            (self::chrToInt($e[31]) & 127) | 64
        );
        # fe_frombytes(x1,p);
        $x1 = self::fe_frombytes($p);
        # fe_1(x2);
        $x2 = self::fe_1();
        # fe_0(z2);
        $z2 = self::fe_0();
        # fe_copy(x3,x1);
        $x3 = self::fe_copy($x1);
        # fe_1(z3);
        $z3 = self::fe_1();

        # swap = 0;
        /** @var int $swap */
        $swap = 0;

        # for (pos = 254;pos >= 0;--pos) {
        for ($pos = 254; $pos >= 0; --$pos) {
            # b = e[pos / 8] >> (pos & 7);
            /** @var int $b */
            $b = self::chrToInt(
                    $e[(int) floor($pos / 8)]
                ) >> ($pos & 7);
            # b &= 1;
            $b &= 1;

            # swap ^= b;
            $swap ^= $b;

            # fe_cswap(x2,x3,swap);
            self::fe_cswap($x2, $x3, $swap);

            # fe_cswap(z2,z3,swap);
            self::fe_cswap($z2, $z3, $swap);

            # swap = b;
            /** @var int $swap */
            $swap = $b;

            # fe_sub(tmp0,x3,z3);
            $tmp0 = self::fe_sub($x3, $z3);

            # fe_sub(tmp1,x2,z2);
            $tmp1 = self::fe_sub($x2, $z2);

            # fe_add(x2,x2,z2);
            $x2 = self::fe_add($x2, $z2);

            # fe_add(z2,x3,z3);
            $z2 = self::fe_add($x3, $z3);

            # fe_mul(z3,tmp0,x2);
            $z3 = self::fe_mul($tmp0, $x2);

            # fe_mul(z2,z2,tmp1);
            $z2 = self::fe_mul($z2, $tmp1);

            # fe_sq(tmp0,tmp1);
            $tmp0 = self::fe_sq($tmp1);

            # fe_sq(tmp1,x2);
            $tmp1 = self::fe_sq($x2);

            # fe_add(x3,z3,z2);
            $x3 = self::fe_add($z3, $z2);

            # fe_sub(z2,z3,z2);
            $z2 = self::fe_sub($z3, $z2);

            # fe_mul(x2,tmp1,tmp0);
            $x2 = self::fe_mul($tmp1, $tmp0);

            # fe_sub(tmp1,tmp1,tmp0);
            $tmp1 = self::fe_sub($tmp1, $tmp0);

            # fe_sq(z2,z2);
            $z2 = self::fe_sq($z2);

            # fe_mul121666(z3,tmp1);
            $z3 = self::fe_mul121666($tmp1);

            # fe_sq(x3,x3);
            $x3 = self::fe_sq($x3);

            # fe_add(tmp0,tmp0,z3);
            $tmp0 = self::fe_add($tmp0, $z3);

            # fe_mul(z3,x1,z2);
            $z3 = self::fe_mul($x1, $z2);

            # fe_mul(z2,tmp1,tmp0);
            $z2 = self::fe_mul($tmp1, $tmp0);
        }

        # fe_cswap(x2,x3,swap);
        self::fe_cswap($x2, $x3, $swap);

        # fe_cswap(z2,z3,swap);
        self::fe_cswap($z2, $z3, $swap);

        # fe_invert(z2,z2);
        $z2 = self::fe_invert($z2);

        # fe_mul(x2,x2,z2);
        $x2 = self::fe_mul($x2, $z2);
        # fe_tobytes(q,x2);
        return (string) self::fe_tobytes($x2);
    }