clipka <ano### [at] anonymousorg> wrote:
> I would think that a good optimizing compiler would translate something 
> like "x = -x;" to equally efficient code...?

  Out of curiosity, I tested how gcc compiles this function with maximum
optimizations (-O3 -ffast-math -march=native):

void negate(double* values, unsigned amount)
{
    for(unsigned i = 0; i < amount; ++i)
        values[i] = -values[i];
}

  The relevant part of the asm output was:

	xorl	%eax, %eax
.L7:
	fldl	(%edi,%eax,8)
	fchs
	fstpl	(%edi,%eax,8)
	addl	$1, %eax
	cmpl	%eax, %esi
	ja	.L7

  So it is loading the values into the FPU one by one, negating them there
and then storing them back into RAM.

-- 
                                                          - Warp

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