Re: [pure-lang-users] math.pure

[Albert G. <Dr....@t-...>]

Eddie Rucker wrote:
>  > pow 0 (-1);
>  <stdin>:2.0-13: unhandled exception 'signal 8' while evaluating 'pow 0
> (-1)'

Yeah, that's just 1 div 0 in disguise there, so it's handled the same 
(see below). Note that GMP's mpz_pow_ui actually raises a SIGFPE in this 
case.

> Did you want to leave this unevaluated or throw an error?
> Also, x div 0 throws and error as well?

Yes, all integer divisions by zero throw a 'signal SIGFPE' exception 
now. In previous releases these would just crap out with an unhandled 
SIGFPE signal generated by the cpu, so this is definitely an improvement. :)

In Q, these return a normal form instead, which gives you the 
opportunity to add your own equations to handle division by zero. But 
this is not possible in Pure (at least not without sacrificing most of 
Pure's arithmetic performance), because integer arithmetic compiles to 
actual machine instructions there.

NB: It would be possible to implement this for the bigint operations as 
these are implemented as calls into the runtime, but I'd rather like 
these to work consistently with the machine int operations. Also, this 
is one of the cases where I think it's not really worth the effort, 
because integer division by 0 almost invariably indicates a serious 
program bug. Finally, note that you can still define x div 0 any way you 
want as long as you're doing symbolic calculations (i.e., x is not an 
integer).

> Should we add the following?
> 
> nan^nan = nan;
> nan^inf = nan;

This already works as of r560.

> pow nan nan = nan;
> pow nan inf = nan;

I'm about to remove the definition of pow on double, it just duplicates 
the functionality of the ^ operator anyway.

Albert

-- 
Dr. Albert Gr"af
Dept. of Music-Informatics, University of Mainz, Germany
Email:  Dr....@t-..., ag...@mu...
WWW:    http://www.musikinformatik.uni-mainz.de/ag