Question

Using a loop and indexed addressing, write assembly language code that rotates the members of a 32-bit integer array forward one position. The value at the end of the array must wrap to the first position. For example, the array [10, 20, 30, 40] would be transformed into [40, 10, 20, 30]

Answer 1

Answer:

Here is the code which will rotate the array.

*************************************************************************

.386

.model flat,stdcall

.stack 4096

ExitProcess PROTO, dwExitCode:DWORD

section .data

array DWORD 10,20,30,40 ; Initialising the array  

arrayType DWORD TYPE array

newArray DWORD LENGTHOF array DUP(?)

lastElement DWORD ?

.code

main PROC

 

   ;First Element will be moved to register ESI

   mov ESI, OFFSET array

   ;Next Array Element in EDI

   mov EDI, OFFSET newArray  

   ADD EDI, TYPE newArray

   ;Loop Counter set into register ECX

   mov ECX, LENGTHOF array

L2:

   mov EAX, [ESI]

   mov [EDI], EAX

   ADD ESI, TYPE array

   ADD EDI, TYPE array

   LOOP L2

   ; following will set the last element of array into first position of newArray

   mov EDI,OFFSET newArray

   mov EAX, [ESI]

   mov [EDI], EAX

INVOKE ExitProcess,0

main ENDP

END main

Explanation:

.386 - It will enable assembly of non privileged instruction for 80386 processor.

.model flat, stdcall - It will explain about which memory to use.  

.stack 4096 - It is used to inform assembler to reserver 4096 bytes of uninitialised memory.

.code is a code section.

section .data is used to declare initialized data.

DWORD is a type specified with 4 bytes address.

EAX, EDI, ESI, ECX are Registers

mov- It will move data from one register to another.

ADD- Add two values.