# 開發紀錄(sandbox)

## Fibonacci 實作

recursive

int fib(int n)
{
    if (n == 0) return 0;
    if (n == 1) return 1;
        
    return fib(n - 1) + fib(n - 2);
}

用 moxie-none-moxiebox-gcc 產生組合語言程式碼

$ moxie-none-moxiebox-gcc -S fib_recursive.c 
$ cat fib_recursive.s
	.file	"fib_recursive.c"
	.text
	.p2align	1
	.global	fib
	.type	fib, @function
fib:
	push	$sp, $r6
	dec	$sp, 24
	sto.l	12($fp), $r0
	ldo.l	$r1, 12($fp)
	xor	$r0, $r0
	cmp	$r1, $r0
	bne	.L2
	xor	$r0, $r0
	jmpa	.L3
.L2:
	ldo.l	$r1, 12($fp)
	ldi.l	$r0, 1
	cmp	$r1, $r0
	bne	.L4
	ldi.l	$r0, 1
	jmpa	.L3
.L4:
	ldo.l	$r0, 12($fp)
	dec	$r0, --1
	jsra	fib
	mov	$r6, $r0
	ldo.l	$r0, 12($fp)
	dec	$r0, --2
	jsra	fib
	mov	$r1, $r6
	add	$r1, $r0
	mov	$r0, $r1
.L3:
	mov	$r12, $fp
	dec	$r12, 4
	pop	$r12, $r6
	ret
	.size	fib, .-fib
	.ident	"GCC: (crosstool-NG crosstool-ng-1.23.0-215-g2196112) 7.2.0"

用 sandbox 執行程式

$ src/sandbox -e tests/fib_recursive
ep 00001000
ro 00000f6c-00001832 elf0
ro 00001834-00001950 elf1
rw 00001a50-0000201c elf2
rw 0000301c-0001301c stack
ro 0001401c-000140dc mapdesc
Sim exception 7 (Bus error)

iterative

int fib(int n)
{
    if (n == 0) return 0;
        
    int prevPrev = 0;
    int prev = 1;
    int result = 0;
 
    while (n > 0)
    {
        n--;
        result = prev + prevPrev;
        prevPrev = prev;
        prev = result;
    }
    return result;
}

用 moxie-none-moxiebox-gcc 產生組合語言程式碼

$ moxie-none-moxiebox-gcc -S fib_iterative.c 
$ cat fib_iterative.s
	.file	"fib_iterative.c"
	.text
	.p2align	1
	.global	fib
	.type	fib, @function
fib:
	dec	$sp, 12
	sto.l	12($fp), $r0
	ldo.l	$r1, 12($fp)
	xor	$r0, $r0
	cmp	$r1, $r0
	bne	.L2
	xor	$r0, $r0
	ret
.L2:
	xor	$r0, $r0
	sto.l	-4($fp), $r0
	ldi.l	$r0, 1
	sto.l	-8($fp), $r0
	xor	$r0, $r0
	sto.l	-12($fp), $r0
	jmpa	.L4
.L5:
	ldo.l	$r0, 12($fp)
	dec	$r0, --1
	sto.l	12($fp), $r0
	ldo.l	$r1, -8($fp)
	ldo.l	$r0, -4($fp)
	mov	$r2, $r1
	add	$r2, $r0
	mov	$r0, $r2
	sto.l	-12($fp), $r0
	ldo.l	$r0, -8($fp)
	sto.l	-4($fp), $r0
	ldo.l	$r0, -12($fp)
	sto.l	-8($fp), $r0
.L4:
	ldo.l	$r1, 12($fp)
	xor	$r0, $r0
	cmp	$r1, $r0
	bgt	.L5
	ldo.l	$r0, -12($fp)
	ret
	.size	fib, .-fib
	.ident	"GCC: (crosstool-NG crosstool-ng-1.23.0-215-g2196112) 7.2.0"