Re: Reading Float Data from a binary file into ada

[Ali Bendriss <Ali.Bendriss@drc.ion.ucl.ac.uk>]

On Tuesday 30 January 2007 16:55, Jean-Pierre Rosen wrote:
> frikk a écrit :
> > 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).
>
> Hmm... This looks like a fixed point representation, not a floating
> point one.
>
There is the same kind of representation in the tiff format,
The "type RATIONAL" two LONGs : the first represent the numerator of the 
fraction, the second the denominator.

> > 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?
>
> In general, Unchecked_Conversion is your friend when you need two
> different views, at differing levels of abstraction, of the same data.
>
I remember doing some Unchecked_Conversion to read a proprietary tiff file 
some time ago. But only to find the LONGs and then after I was just doing a 
simple division to get the result. 

> > Basically I need to be able to read in the binary data byte by byte
> > but store it into a 32 bit Float.
>
It may be helpfull to know some value in advance like a magic number.

> However, if you do an unchecked_conversion to Float, it will certainly
> not work, because your data don't look at all like floats!

-- 
Ali