Re: Reading Float Data from a binary file into ada

On Jan 30, 3:02 pm, Martin Dowie <martin.do...@xxxxxxxxxxxxxxxxxxxxxx>
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

.

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