string to char array?

[Kyoji Klyden via Digitalmars-d-learn]

On Friday, 5 June 2015 at 18:30:53 UTC, Kagamin wrote:
> Well, reading assembler is good enough:
>
> void f(int[] a)
> {
>   a[0]=0;
>   a[1]=1;
>   a[2]=2;
> }
>
> Here pointer is passed in rsi register and length - in rdi:
>
> void f(int[]):
> 	push	rax
> 	test	rdi, rdi
> 	je	.LBB0_4
> 	mov	dword ptr [rsi], 0
> 	cmp	rdi, 1
> 	jbe	.LBB0_5
> 	mov	dword ptr [rsi + 4], 1
> 	cmp	rdi, 2
> 	jbe	.LBB0_6
> 	mov	dword ptr [rsi + 8], 2
> 	pop	rax
> 	ret
> .LBB0_4:
> 	mov	edi, 55
> 	mov	esi, .L.str
> 	mov	edx, 5
> 	call	_d_arraybounds
> .LBB0_5:
> 	mov	edi, 55
> 	mov	esi, .L.str
> 	mov	edx, 6
> 	call	_d_arraybounds
> .LBB0_6:
> 	mov	edi, 55
> 	mov	esi, .L.str
> 	mov	edx, 7
> 	call	_d_arraybounds
>
> You play with assembler generated for D code at 
> http://ldc.acomirei.ru/

Never said I was good at asm but I'll give it a shot...

So push rax to the top of the memory stack, test if rdi == rdi 
since yes jump to.LBB0_4, in LBB0_4 move the value 55 into edi, 
then move .L.str (whatever that is) into esi, then 5 into edx, 
then call _d_arraybounds (something from Druntime maybe?) then 
LBB0_4 has nothing left so go back, move the value 0 into a 
32-bit pointer(to rsi register), if rdi == 1 jump to LBB0_5 
(pretty much the same as LBB0_4), then move 1 into the pointer 
(which points to rsi[+ 4 bytes cuz it's an int]), so on and so 
forth until we pop rax from the memory stack and return.

How did I do? :P (hopefully at least B grade)

I'm not really sure what .L.str or _d_arraybounds is, but I'm 
guessing it's the D runtime?

Also in the mov parts, is that moving 1 into the pointer or into 
the rsi register? And is rsi + 4, still in rsi, or does it move 
to a different register?