Hi Taylor,
I do agree but it's only *mostly* absurd I would argue. :)
If I know I have a flonum within a known range, and I always want it as
a fixnum, then this does the job, and I imagine skips a bunch of checks
that would be irrelevant in this case (pls correct me if wrong though!)
If you use (##c-code ... ) inline then the C callout is gone... and on
GCC / Intel the conversion will compile to a cvttsd2si instruction.
I am just putting a pragmatic / performance view here, it's definitely
not elegant.
Obviously if inexact->exact has higher performance, eg because it's an
optimizable intrinsic, then this method is categorically rubbish. :) I
haven't checked yet though.
Cheers,
Darren
Taylor R Campbell wrote:
> Date: Thu, 30 Oct 2008 08:37:32 +1000
> From: Darren Baker <darren@wildfire.com.au>
>
> This is no doubt Very Bad Practice but it's useful :)
>
> (define flonum->fixnum
> (c-lambda (double) int "___result = (int)___arg1;"))
>
> That's absurd! Aside from the obvious absurdity of calling out to C
> for this, it leads to nasal demons if the range of the argument's
> integral part exceeds the range of C ints or Gambit fixnums. There is
> a perfectly good standard procedure to obtain the nearest exact number
> to an inexact one, which one may have obtained by rounding another
> inexact number. This procedure is called INEXACT->EXACT.
>
>
>--Ph: +61 7 3844 1000
Darren Baker
CEO, CTO
Wildfire Studios Pty. Ltd.
Fax: +61 7 3844 8970
www.wildfire.com.au
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