Re: Float conversion

["Jeffrey R. Carter" <spam.jrcarter.not@spam.acm.org>]

On 07/29/2010 11:21 AM, Henrique wrote:
>
> As I declared the type with 6 digits, I expected that it would make
> the comparison only for these digits (this would gave var4 = var1).

"digits N" means the compiler will use at least Ceiling (N * log2 (10) ) bits 
for the mantissa, 'Image will produce a string with N digits, and an 
instantiation of Ada.Text_IO.Float_IO will output N digits by default. There was 
an effect on the minimum size of the exponent in Ada 83, but I don't think that 
applies any more. (There are probably other cases as well where the "digits" 
value has an effect that I can't think of at the moment.) But all operations, 
including comparisons, take place in the underlying implementation or with 
greater precision.

Most x86-type processors have HW floating-point types that correspond to digits 
7, 15, and 18 (IIRC), so on such a machine you should expect your compiler to 
choose one of those. All computations are done using the digits-18 
representation, so there doesn't seem to be much reason to choose another 
representation.

-- 
Jeff Carter
"Well, a gala day is enough for me. I don't think
I can handle any more."
Duck Soup
93