MASM (Assembly programming) This question is not from a textbook, but the textbo

Question

MASM (Assembly programming)

This question is not from a textbook, but the textbook used during course:

Assembly Language for x86 Processors, 6th Edition, by Irvine

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Question:

Using bit-wise Boolean operations (AND, OR, XOR, NOT, TEST), and NO arithmetic operations (ADD, SUB, MUL, NEG, CMP, ...), write a program that receives a signed number in the AX register, and alters this (returning answer in AX) as follows using ONLY four bit-wise Boolean operations:

1. If the number is negative, say -n, then replace it with the non-negative number n-1, and then

2. If the number is divisible by 8, then add 6 to it, and then

3. If it is even, add one to it, but if it is odd, subtract one from it.

Explanation / Answer

leaq -4(%rbp), %rax movq %rax, %rsi movl $_ZSt3cin, %edi .LEHB0: call _ZNSirsERi .LEHE0: movl -4(%rbp), %eax testl %eax, %eax jns .L2 movl -4(%rbp), %eax subl $1, %eax movl %eax, -4(%rbp) .L2: movl -4(%rbp), %eax andl $7, %eax testl %eax, %eax jne .L3 movl -4(%rbp), %eax addl $6, %eax movl %eax, -4(%rbp) .L3: movl -4(%rbp), %eax andl $1, %eax testl %eax, %eax jne .L4 movl -4(%rbp), %eax addl $1, %eax movl %eax, -4(%rbp) jmp .L5 .L4: 0051 8B45FC movl -4(%rbp), %eax 0054 83E801 subl $1, %eax 0057 8945FC movl %eax, -4(%rbp)

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