From mboxrd@z Thu Jan  1 00:00:00 1970
Message-ID: <c1a1c2a6f971c9fbe256fe84f23cb152@plan9.bell-labs.com>
To: 9fans@cse.psu.edu
Subject: Re: [9fans] p9/linux/fbsd compiler shootout
From: "rob pike" <rob@plan9.bell-labs.com>
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Date: Tue, 26 Feb 2002 09:18:36 -0500
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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