Re: How to put 200 into an integer sub-type of 16 bits (code included)

[Stephen Leake <stephen_leake@stephe-leake.org>]

ChristopherL <clusardi2k@aol.com> writes:

> On Jan 14, 12:41 pm, Adam Beneschan <a...@irvine.com> wrote:
>> On Jan 14, 12:13 pm, ChristopherL <clusard...@aol.com> wrote:
>>
>> > I want to copy bits from an Ada float to a user defined short integer
>> > maintaining the same
>> > bit representation.
>>
>
> This problem was given to me to try to solve who said it's probably
> impossible!

Ok. This could eventually be used to verify the floating point format
used by your machine, for example.

The right way to proceed is to write a bit-level record clause for the
floating point type on your hardware; something like:

type unsigned_24 is ...;
type usigned_7 is ...;

type IEEE_32_Float_Rep_Type is record
    sign : boolean;
    exponent : unsigned_7;
    mantissa_1 : Interfaces.unsigned_8;
    mantissa_2 : Interfaces.unsigned_8;
    mantissa_3 : Interfaces.unsigned_8;
end record;

for IEEE_32_Float_Rep_Type use record
    sign : at 0 range 0 .. 0;
    exponent : at 0 range 1 .. 8;
    mantissa_1 : at 0 range 9 .. 15;
    mantissa_2 : at 0 range 16 .. 23;
    mantissa_3 : at 0 range 24 .. 31;
end record;

Note that I broke the mantissa down into three parts, each fitting in
8 bits.

I probably have the details wrong for IEEE 32 bit float; look it up
somewhere.

Especially note that the 'range' values need to have the correct
endianness for your machine (sign will be at 31 on some machines, 0 on
others).

Then use unchecked conversion from float to IEEE_32_Float_Rep_type,
then simple assignment (possibly with an integer type conversion) from
any field to an Unsigned_8.

--
-- Stephe