Re: Fortran's Equivalence

[sampson@nosc.mil (Charles H. Sampson)]

In article <dewar.860159911@merv>, Robert Dewar <dewar@merv.cs.nyu.edu> wrote:

>Note incidentally one HUGE advantage of overlays over the use of
>unchecked conversion, which is that if you use uncheckd conversion,
>you always have to do two of them to make a modification. Consider
>a case where we want an array of 32-bit integers overlaid by an
>array of 32-bit floats.
>
>Now if you do this by declaring an array of 32-bit floats and then
>doing unchecked conversion to 32-bit integer, you will end up doing
>
>    x(J) := To_Float_32 (Fiddle (To_Integer_32 (x(J))));
>
>which is MUCH more more inpenetrable than:
>
>    x_Int (J) := Fiddle (X_Int (J));
>
>Of course it is always a matter of taste whether you want to emphasize
>the nature of what you are doing by writing the explicit stuff each
>time. A legitimate objection to the second form here might be that
>it is TOO easy to write and read!

     I would be one of the objectors, except that I would characterize 
it as not easy to read.  The wordy form above says pretty clearly what's 
going on: Take the bits that make up the value of x(j), treat them as a 
32-bit integer, fiddle with the result, treat those bits as a floating-
point value, and assign them to x(j).  None of that information is imme-
diately available in the shorted version.  It lacks an attribute that I 
call "local understandability".

				Charlie