USING x86 ASSEMBLY LANGUAGE: PART 1: Given a byte (x), swap every even bit with

Question

USING x86 ASSEMBLY LANGUAGE:

PART 1: Given a byte (x), swap every even bit with its adjacent odd bit. For example 100 in decima!l is represented as 81108180 in a byte (or 8 bits). If we swap the even bits with their adjacent odd bits, we get 18811000, which is 152 in decimal. Implementation details: The input integer is stored in registers cl. You need to store the answer into register al. unsigned char swapBits(unsigned char x) unsigned char result; asm xor al, al mov cl,x /YOUR CODE STARTS HERE / YOUR CODE ENDS HERE mov result, al return result;

Explanation / Answer

Part 1:

Please find below code, and let me know in case of any error/doubt in the comment.

code:

__asm

{

xor al, al
mov cl, x

and cl, 0x55555555
shl cl, 1
mov al, x
and al, 0xAAAAAAAA
shr al, 1
or al, cl
mov result, al

}

Part 2:

Please check below code and let me know in case of any error or doubt in the comment:

section .text

global _start

section .data:

global result

result:

db 0

_start:

xor eax, eax

mov esi, result

  

mov ebx, a

mov ecx, b

  

test ebx, 3

jnz not_multiple_of_4

and ebx, 0x0F

shl ebx, 4

and a, 0xF0

shr a, 4

or ebx, a

add ebx, b

mov eax, ebx

_not_multiple_of_4:

; ...

and ecx, 0x0F

shl ecx, 4

and b, 0xF0

shr b, 4

or ecx, b

add ecx, a

mov eax, ecx

mov[esi][0], eax

retn

  

section .bss:

mov eax, 1

int 0x80   

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