Re: Unsigned Integer Restraint Errors

["Adam Beneschan" <adam@irvine.com>]

On Mar 13, 7:58 am, "frikk" <frik...@gmail.com> wrote:
> I have a bit of an unrelated (but kind of related) question:
>
> Are there any builtin square root functions? I thought this was
> working, but I don't think it is anymore:
> m := Integer(100**(0.5)+1);

This couldn't have worked as written, since there is no predefined
"**" that accepts a floating-point number on the right side.

> This always coming out to 2. I;m using this to computer a maximum loop
> value for finding primes. I'd like to loop from 2 to sqrt(n)/2 + 1.
>
> Any suggestions?

See Section A.5.1.  Ada.Numerics.Elementary_Functions (A.5.1(9))
defines Sqrt as well as a "**" that accepts floating-point exponents.

By the way, if I were going to write a loop that goes from 2 to
sqrt(n)/2 + 1, I wouldn't use Sqrt like this:

    for I in 2 .. Integer(Float'Floor(Sqrt(Float(N))/2.0)) + 1 loop...

but rather, I'd just write it something like this:

    I := 2;
    while (2 * I - 1) * (2 * I - 1) <= N loop -- I think I got this
right
        ...
        I := I + 1;
    end loop;

on the theory that using Sqrt is just a waste of cycles when you can
just use integer arithmetic.  But I've been programming for way too
long---long enough that I remember what a Hollerith card is---and I'm
sure that doing a square-root doesn't take nearly as long as it used
to, so there are probably some reasonable values of N for which
computing the square-root first makes things more efficient than the
repeated integer multiplications.  I don't know.  Use Sqrt if you want
to.

                                 -- Adam