From: "rob pike" <rob@plan9.bell-labs.com>
To: 9fans@cse.psu.edu
Subject: Re: [9fans] p9/linux/fbsd compiler shootout
Date: Tue, 26 Feb 2002 09:18:36 -0500 [thread overview]
Message-ID: <c1a1c2a6f971c9fbe256fe84f23cb152@plan9.bell-labs.com> (raw)
Again, and strongly, there was little effort made to make the Plan 9
C compilers generate good floating point code. I predict much less
difference using normal, integer code - such as the kernel - which
did receive some optimization attention.
Also, the kernel spends most of its time in memmove and memset,
both of which are written in assembler and therefore are not affected
by the compiler. I doubt the quality of complation of the kernel has a
minor effect on runtime of the compiler itself.
Russ Cox points out that:
the linux guys
decided that the default floating-point
precision should be 80-bit in-register
precision but with 64-bit in-memory
precision. i realize that this is sometimes
desirable if you know what you're doing,
but they made it the default. so code
ends up behaving differently (usually
incorrectly) based on what gcc registerizes
and what overflows into memory.
#include <stdio.h>
#include <stdlib.h>
#include <math.h>
void
main(void)
{
double x, y;
x = sqrt(3.0);
y = sqrt(3.0) - x;
if(y)
printf("buggered\n");
}
-rob
next reply other threads:[~2002-02-26 14:18 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2002-02-26 14:18 rob pike [this message]
-- strict thread matches above, loose matches on Subject: below --
2002-02-26 15:02 andrey mirtchovski
2002-02-26 16:02 ` Wilhelm B. Kloke
2002-02-26 18:00 ` splite
2002-02-26 16:04 ` Matt H
2002-03-04 10:04 ` Gaute B Strokkenes
2002-02-26 14:20 rob pike
2002-02-26 16:07 ` Sean Quinlan
2002-02-26 11:15 forsyth
2002-02-26 3:10 rob pike
2002-02-26 10:26 ` Thomas Bushnell, BSG
2002-02-26 3:05 andrey mirtchovski
2002-02-26 10:27 ` Thomas Bushnell, BSG
2002-02-26 10:27 ` Thomas Bushnell, BSG
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