Re: Reading Float Data from a binary file into ada

["Steve" <nospam_steved94@comcast.net>]

"frikk" <frikker@gmail.com> wrote in message 
news:1170172307.292500.256090@m58g2000cwm.googlegroups.com...
> Hello everyone! I am having a problem that I would love some help
> with.
>
> Essentially I was given a Visual Basic program that dumps a binary
> configuration file with all of the variables in a set.  The variables
> are each 32 bit floats, with the first 16 bits being the integer part
> and the second 16 bits being a representation of the fraction (I'm not
> sure if this is stanard - but its just how VB dumps the data). The
> binary dump is basically a copy of the way VB stores the data in
> memory.  I need to be able to use this data in ada.  There is a C
> counterpart to this that makes use of a 'union' to grab the data 1
> byte (8 bits) at a time, put them into a char array of size 4, then
> use a 32 bit float to reference the data.  Is there somehow I can do
> this in ada as well?

Your description of how the C counterpart works is inconsistant with the way 
you have described the data format in the file.

If the C program is using a union to view the data as either a float or a 4 
character array then it is very likely that the data is in fact stored in 
IEEE 754 floating point format.  If you are using Microsoft's C compiler 
this is certainly the case.

The following snippet contains the pieces you need to do the conversion.

      TYPE aByte IS MOD 256;

      FOR aByte'SIZE USE 8;

      TYPE aByteArray IS ARRAY( Positive RANGE <> ) OF aByte;

      PRAGMA PACK( aByteArray );

      TYPE aFourBytes IS NEW aByteArray(1..4);

      FUNCTION Conv IS NEW Ada.Unchecked_Conversion( aFourBytes, float );

      ...

      a : float;
      b : aFourBytes;

      ...

      a := Conv( b )

Use unchecked conversion to convert from a type that contains 4 bytes to the 
float value you're looking for.

Regards,
Steve
(The Duck)

>
> Basically I need to be able to read in the binary data byte by byte
> but store it into a 32 bit Float.  The C union example above uses the
> same memory address for the Float as it does for the size 4 char
> array. I don't even know if the VB dump will correspond with the way
> ada handles floats or not, but I'll worry about that later.
>
> I am also using Matlab/Simulink if that provides any additional tools
> to use for debugging.
>
> Thank you for any help,
> Blaine
>