问题
In some homework, I have to create a Fibonacci Sequence program in Assembly. I created this code, but it doesn't seem to be working correctly and I am not sure as to why. I believe that I am doing this correctly, but EAX remains "2" every loop.
INCLUDE Irvine32.inc
.data
prev DWORD ?
next DWORD ?
val DWORD ?
count DWORD ?
total DWORD ?
myMsg BYTE "Fibonacci Sequence ",0dh,0ah,0
.code
main PROC
mov ecx,15
mov val,1
mov prev,-1
mov eax,1
mov edx,OFFSET myMsg
call WriteString
L1:
mov count,ecx
mov ebx,val
add ebx,prev
mov total,ebx
mov ebx,val
mov prev,ebx
mov eax,total
mov val, ebx
call WriteInt
call Crlf
loop L1
exit
main ENDP
END main
回答1:
Could look like this (untested):
mov ecx, 15
mov eax, 0 ;a = 0
mov ebx, 1 ;b = 1
_fib:
mov edx, eax
add edx, ebx ;sum = a + b
mov eax, ebx ;a = b
mov ebx, edx ;b = sum
loop _fib
回答2:
Your loop simplifies to this in pseudocode:
L1:
count = ecx; // count === 15
eax = total = val + prev; // prev = -1 => eax = 0. prev = 1 => eax = 2
prev = val; // sets prev = 1, val doesn't change so prev = 1 after the first iteration
As you can see, eax = val + prev will evaluate to 2 once prev gets set to 1.
You should elaborate on the specification of your problem. How many integers do you want to print out? Is this what count = 15 is for? In that case you need to be decreasing count with every iteration and checking to see that it is non-zero.
As for the Fibonacci sequence, you should be doing something like this in your loop:
// lets say that eax is the current integer in the sequence and prev is the previous integer
// then the next integer = eax + prev
ebx = eax + prev
prev = eax
eax = ebx
来源：https://stackoverflow.com/questions/9607217/non-recursive-fibonacci-sequence-in-assembly