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Re: Fast operations on floating point numbers?
- From: Peter Barada <peter at the-baradas dot com>
- To: martin at MPA-Garching dot MPG dot DE
- Cc: gcc at gcc dot gnu dot org
- Date: Thu, 4 Dec 2003 08:53:57 -0500 (EST)
- Subject: Re: Fast operations on floating point numbers?
- References: <3FCF05D6.8070301@mpa-garching.mpg.de>
>I'm not completely sure whether this question belongs to a C/C++ newsgroup,
>but it is probably compiler-specific, so I'm trying my luck here.
>
>I'm developing a numerical simulation code which contains operations
>like this one
>
>double a;
>int flipsign;
>
>[...]
>
>if (flipsign)
> a = -a;
>
>in an inner loop which is executed billions of times.
>I suspect that the conditional slows the execution down,
>and the "a=-a" statement might not be optimal as well.
If flipsign is only refered to inside the(hevily executed) loop, you
could try:
double a, flip;
int flipsign;
flip = flipsign ? -1.0 : 1.0;
for (;;) {
...
a *= flip;
...
}
And get rid of the conditional...
--
Peter Barada
peter@the-baradas.com