ARM中的遞歸斐波那契

Question

我試圖將這個遞歸斐波那契碼轉換爲ARM彙編語言。我是新手，並不確定如何去做。我有一些我已經在下面玩過的代碼片段。

Fib (n) { 
    if (n == 0 || n == 1) return 1; 
    else return Fib(n-2) + Fib(n-1); 
    } 

這是迄今爲止我嘗試：

RO = 1 
    CMP RO #1 
    BGT P2 
    MOV R7 #1 
    B END 
P2: 
    END LDR LR [SO,#0] 
    ADD SP SP, #8 
    MOV PC, LR 

幫助，將不勝感激

Answer 1

爲了避免填鴨式的緣故，我寫道，發現使用遞歸斐波那契序列的LEGv8程序。 LEGv8是略微不同於ARMv8，但算法仍然存在。

請檢查代碼，並將命令/寄存器更改爲其在ARMv8中的相應值。

我假設n（Fibonacci序列的範圍）存儲在寄存器X19中。

我還假設我們應該將Fibonacci序列存儲在一個數組中，該數組的基地址存儲在X20中。

MOV X17, XZR // keep (previous) 0 in X17 for further use 
    ADDI X18, XZR, #1 // keep (Current) 1 in X18 for further use 
    ADDI X9, XZR, #0 // Assuming i = 0 is in register X9 
fibo: 
    SUBI SP, SP, #24 // Adjust stack pointer for 3 items 
    STUR LR, [SP, #16] // save the return address 
    STUR X17, [SP, #8] //save content of X17 on the stack 
    STUR X18, [SP, #0] //save content of X18 on the stack 
    SUBS X10, X9, X19 // test for i==n 
    CBNZ X10, L1 // If i not equal to n, go to L1 
    MOV X6, XZR // keep 0 on X6  
    ADDI X5, XZR, #1 // keep 1 on X5 
    ADDI X2, X9, #1 //X9 increased by 1 for further use 
    STUR X6, [X20,#0] //store 0 in the array 
    STUR X5, [X20, #8] //store 1 in the array 
    ADDI SP, SP, #24 // pop 3 items from the stack 
    BR LR // return to the caller 
L1: 
    ADD X16, X17, X18 // Next_Num = previous + Current 
    MOV X17, X18 // Previous = Current 
    MOV X18, X16 // Current= Next_Num 
    ADDI X9, X9, #1 // i++ 
    BL fibo // call fibo 
    LDUR X18, [SP, #0] // return from BL; restore previous 
    LDUR X17, [SP, #8] // restore current 
    LDUR LR, [SP, #16] // restore the return address 
    ADDI SP, SP, #24 // adjust stack pointer to pop 3 items 
    ADD X7, X18, X17 // keep (previous + current) value on register X7 
    LSL X2, X2, #3 // Multiplying by 8 for offset  
    ADD X12, X20, X2 // address of the array increase by 8 
    STUR X7, [X12, #0] // store (previous + current) value on the array 
    SUBI X2, X2, #1 // X9 decreased by 1 
    BR LR // return