Re: Reading Float Data from a binary file into ada

[Martin Dowie <martin.dowie@btopenworld.com.delete>]

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