Type casting question

[Raju Vemulamanda <raju@tridsys.com>]

Question: Could someone please provide some solution
  to the below?

I have this question in the conversion of values
between the string and the my own type shown below.

type Bit_5 is range 2#0# .. 2#11111#;
    for Bit_5'Size use 5;
subtype Size_Type is Bit_5;

The above is how Size_Type has been declared.

val1 : Jvmfr3_Field_Types.Size_Type := 10;

Suppose I have a string xxx which has the some value in it,
How can I convert that xxx into the above declared val1?
I have to copy xxx into val1. I need to somehow do the
type casting for the above.