Re: Reading Float Data from a binary file into ada

["frikk" <frikker@gmail.com>]

On Jan 30, 3:02 pm, Martin Dowie <martin.do...@btopenworld.com.delete> 
wrote:
> frikk wrote:
> > 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?
>
> > 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.
>
> Here's a small example that I think shows what you need (doesn't deal
> with any endian issues!) and goes the other way to what you need
> (fixed-point -> unsigned 32-bit) but you'll get the idea.
>
> The one line I'm not sure about is if both 'Small and 'Size are needed -
> I always use both but I think 'Size may not strictly be needed.
>
> Hope this helps!
> Cheers
> -- Martin
>
> -- File: fp_example.adb
> with Ada.Text_IO; use Ada.Text_IO;
> with Ada.Unchecked_Conversion;
>
> with Interfaces; use Interfaces;
>
> procedure FP_Example is
>
>     -- Defines the LSB
>     FP_Delta : constant := 2.0**(-16);
>
>     type FP is delta FP_Delta range -2.0**15 .. 2.0**15-FP_Delta;
>     for FP'Small use FP_Delta;
>     for FP'Size  use 32;
>
>     F1 : FP := FP'First;
>     F2 : FP := FP'Last;
>
>     package FP_IO is
>        new Ada.Text_IO.Fixed_IO (FP);
>     use FP_IO;
>
>     package Unsigned_32_IO is
>        new Ada.Text_IO.Modular_IO (Unsigned_32);
>     use Unsigned_32_IO;
>
>     function To_Unsigned_32 is
>        new Ada.Unchecked_Conversion (Source => FP,
>                                      Target => Unsigned_32);
> begin
>     Put (F1, Aft => 16); New_Line;
>     Put (F2, Aft => 16); New_Line;
>     Put (To_Unsigned_32 (F1), Base => 16); New_Line;
>     Put (To_Unsigned_32 (F2), Base => 16); New_Line;
> end FP_Example;
>
> c:\ada\fp_example\fp_example.exe
> -32768.0000000000000000
>   32767.9999847412109375
> 16#80000000#
> 16#7FFFFFFF#
> process terminated successfully- Hide quoted text -
>
> - Show quoted text -

Niklas - I think this is exactly what I need to do.

Martin - Thank you for the example. I will go through that and see 
what I can use - it looks very useful though.  May I get some 
clarification on exactly what this line does:
    type FP is delta FP_Delta range -2.0**15 .. 2.0**15-FP_Delta;
    for FP'Small use FP_Delta;
    for FP'Size  use 32;

What is the delta used for?

Thanks!
Blaine