Performance

[bearophile via Digitalmars-d]

> double plus(in uint nSteps) pure nothrow @safe /*@nogc*/ {
>     enum double p0 = 0.0045;
>     enum double p1 = 1.00045452-p0;
>
>     double tot = 1.346346;
>     auto b = true;
>
>     foreach (immutable i; 0 .. nSteps) {
>         final switch (b) {
>             case true:
>                 tot += p0;
>                 break;
>             case false:
>                 tot += p1;
>                 break;
>         }
>
>         b = !b;
>     }
>
>     return tot;
> }

And this is the 32 bit X86 asm generated by ldc2 for the plus 
function:

__D4test4plusFNaNbNfxkZd:
	pushl	%ebp
	movl	%esp, %ebp
	pushl	%esi
	andl	$-8, %esp
	subl	$24, %esp
	movsd	LCPI0_0, %xmm0
	testl	%eax, %eax
	je	LBB0_8
	xorl	%ecx, %ecx
	movb	$1, %dl
	movsd	LCPI0_1, %xmm1
	movsd	LCPI0_2, %xmm2
	.align	16, 0x90
LBB0_2:
	testb	$1, %dl
	jne	LBB0_3
	addsd	%xmm1, %xmm0
	jmp	LBB0_7
	.align	16, 0x90
LBB0_3:
	movzbl	%dl, %esi
	andl	$1, %esi
	je	LBB0_5
	addsd	%xmm2, %xmm0
LBB0_7:
	xorb	$1, %dl
	incl	%ecx
	cmpl	%eax, %ecx
	jb	LBB0_2
LBB0_8:
	movsd	%xmm0, 8(%esp)
	fldl	8(%esp)
	leal	-4(%ebp), %esp
	popl	%esi
	popl	%ebp
	ret
LBB0_5:
	movl	$11, 4(%esp)
	movl	$__D4test12__ModuleInfoZ, (%esp)
	calll	__d_switch_error

Bye,
bearophile