汇编程序(TASM)计算提高m到n的幂(m ^ n) [英] assembler program (TASM) calculate raise m to the power of n (m^n)

问题描述

我已经编码了程序的一半.问题是我不知道如何编码数学运算部分是将m提高到n (m^n)的功效.那么，对于我的初学者有什么建议吗?

I have already coded half of the program. The problem is I don't know how to code math operation part is raise m to the power of n (m^n). So, any advise for me as a beginner?

.MODEL SMALL

.DATA

greet   db 13,10, "Welcome to Simple Calculator: Raise m to the power n. $"
msg1    db 13,10, 0AH,0DH,"Please enter integer (m:-99 to 99): $"
m       db 3,4 dup(?)
msg2    db 10,13, 0AH,0DH,"Please enter power (n:1 to 9): $"
n       db 3,4 dup(?)
total   db 10,13, "Answer: $"


.CODE

START:

mov ax, seg greet
mov ds, ax
mov dx, offset greet
mov ah, 09h     ;Display message
int 21h 

mov ax, seg msg1
mov ds, ax
mov dx, offset msg1
mov ah, 09h
int 21h         ;Print a message

mov ah, 0ah
mov dx, offset m
int 21h         ;Get 'm' value


n_POWER:

mov ax, seg msg2
mov ds, ax
mov dx, offset msg2
mov ah, 09h
int 21h         ;Print a message

mov ah, 0ah
mov dx, offset n    ;Get 'n' value
int 21h

mov ax, m
mov n, ax
mul ax, n
mov total, n

finish:
mov ah, 09h ;Display message
int 21h

mov ax,4c00h    ;Return control to DOS
int 21h         
end start

此外，我如何从用户那里获得否定输入(例如-99)?

Also, how can I get the negative input from the user (eg. -99) ?

推荐答案

您可以按照以下方式重复乘法:

You can either repeat the multiplication as in:

int result = 1;  while (exp-->0) { result *= base; } return result;

或者，您可以/应该以二进制表示形式处理指数:

or, you can / should treat the exponent in it's binary representation:

5^13 = 5^(0b1101) = 1*(5^1)*(5^4)*(5^8)

因此，一个人可以重复对基数5:5-> 25-> 625-> 390625进行平方的副本，并将那些在指数的二进制表示形式中具有相应位的项相乘.

One can thus repeatedly square a copy of the base 5: 5 -> 25 -> 625 -> 390625 and multiply those terms that have a corresponding bit set in the binary representation of the exponent.

这对于16位算术来说可能是过高的，但是如果您的教授要求您改为执行模块化指数(如非对称密码术中所用)，这将很方便.

This may be overkill for 16-bit arithmetic, but it'll be handy if your professor asks you to perform a modular exponentation instead (as used in asymmetric cryptography).

这两种方法都需要使用有条件的跳转:

Both methods require using conditional jumps:

要有条件地重复cx个操作，只需简单地执行一次操作即可:

to conditionally repeat cx number of operations one simply does:

         mov cx, 13
label:   nop  // put your block of code here
         nop
         loop label;  // The instruction at label will be executed 13 times
         // and cx will end up being zero

要测试是否已设置，可以做

To test a bit being set, one can do

         mov dx, 13      ;; let's have the exponent here
label:   test dx, 1      ;; check if the first bit is zero
                         ;; test performs bitwise _and_ between the operand
                         ;; and sets ZERO flag (among other things)
         jz   notset     
         nop             ;; insert here the statements to be executed
                         ;; when the bit in the exponent is set
notset:  shr dx, 1       ;; shift out the least significant bit -- this also
                         ;; sets the ZERO_FLAG if dx goes to zero
                         ;; (and it eventually does)
         jne label;      ;;

顺便说一句. JNE ==如果不等于也测试零标志，则跳转. 如果不为零，则表示跳转.

btw. JNE == Jump if Not Equal also tests for zero flag. It's synonymous to Jump if Not Zero.

这篇关于汇编程序(TASM)计算提高m到n的幂(m ^ n)的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！