Re: fixed point vs floating point

[dewar@merv.cs.nyu.edu (Robert Dewar)]

Seymour says

<<I'd have to double check whether it's been fixed in Ada 95, but it used
to be that you had to define fixed point types with a range slightly
larger than the intended range in order to ensure that the arithmetic
model mapped properly into the problem domain.
>>

Semour is referring to the permission, present in Ada 83 and Ada 95 to
shrink end-points by delta, This allows the convenience of such
declarations as

   type x is delta 2 ** -31 range -1.0 .. +1.0;

whereas if this freedom did not exist, one would have to say

   type x is delta 2 ** -31 range -1.0 .. +1.0 - 2 ** 31;

(assuming a 2's complement machine ...)

Of course in practice if you write a declaration like

   type x is delta 0.25 range -10.0 .. +10.0;

the endpoints *will* be included.

This was simply a choice of which case to require the explicit fudging
in, and does indeed cause a fair amount of confusion.