ParagonIE_Sodium_Core32_X25519::edwards_to_montgomery

    public static function edwards_to_montgomery(
        ParagonIE_Sodium_Core32_Curve25519_Fe $edwardsY,
        ParagonIE_Sodium_Core32_Curve25519_Fe $edwardsZ
    ) {
        $tempX = self::fe_add($edwardsZ, $edwardsY);
        $tempZ = self::fe_sub($edwardsZ, $edwardsY);
        $tempZ = self::fe_invert($tempZ);
        return self::fe_mul($tempX, $tempZ);
    }