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Date: Tue, 11 Mar 2003 15:09:13 -0800
From: Andrew Morton <akpm@digeo.com>
To: Linus Torvalds <torvalds@transmeta.com>
Cc: george@mvista.com, felipe_alfaro@linuxmail.org, cobra@compuserve.com,
       linux-kernel@vger.kernel.org
Subject: Re: Runaway cron task on 2.5.63/4 bk?
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Linus Torvalds <torvalds@transmeta.com> wrote:
>
> 
> On Tue, 11 Mar 2003, Andrew Morton wrote:
> > 
> > gcc will generate 64bit * 64bit multiplies without resorting to
> > any library code
> 
> However, gcc is unable to do-the-right-thing and generate 32x32->64 
> multiplies, or 32x64->64 multiplies, even though those are both a _lot_ 
> faster than the full 64x64->64 case.

2.95.3 and 3.2.1 seem to do it right?



long a;
long b;
long long c;

void foo(void)
{
	c = a * b;
}



	.file	"t.c"
	.version	"01.01"
gcc2_compiled.:
.text
	.align 4
.globl foo
	.type	 foo,@function
foo:
	pushl %ebp
	movl %esp,%ebp
	movl a,%eax
	imull b,%eax
	movl %eax,c
	cltd
	movl %edx,c+4
.L2:
	movl %ebp,%esp
	popl %ebp
	ret
.Lfe1:
	.size	 foo,.Lfe1-foo
	.comm	a,4,4
	.comm	b,4,4
	.comm	c,8,4
	.ident	"GCC: (GNU) 2.95.3 20010315 (release)"