Question

Assembly Program/Language

Textbook: Introduction to 64 Bit Assembly Programming for Linux and OS X, 3rd Edition, Ray Seyfarth

Chapter 7 - Exercise 1 & 2:

1. Write an assembly program to count all the 1 bits in a byte stored in memory. Use repeated code rather than a loop.
2. Write an assembly program to swap 2 quad-words in memory using xor. Use the following algorithm:

     a = a ^ b      b = a ^ b      a = a ^ b

Answer 1

Ans:-

Program to swap 2 quads-words in a memory using XOR:-

push rbp

mov rbp, rsp

mov DWORD PTR [rbp-20], edi

mov DWORD PTR [rbp-24], esi

mov DWORD PTR [rbp-28], edx

mov DWORD PTR [rbp-32], ecx

mov eax, DWORD PTR [rbp-24]

mov edx, DWORD PTR [rbp-20]

mov ecx, eax

shr edx, cl

mov eax, DWORD PTR [rbp-32]

mov esi, -1

mov ecx, eax

sal esi, cl

mov eax, esi

not eax

and eax, edx

mov DWORD PTR [rbp-4], eax

mov eax, DWORD PTR [rbp-28]

mov edx, DWORD PTR [rbp-20]

mov ecx, eax

shr edx, cl

mov eax, DWORD PTR [rbp-32]

mov esi, -1

mov ecx, eax

sal esi, cl

mov eax, esi

not eax

and eax, edx

mov DWORD PTR [rbp-8], eax

mov eax, DWORD PTR [rbp-4]

xor eax, DWORD PTR [rbp-8]

mov DWORD PTR [rbp-12], eax

mov eax, DWORD PTR [rbp-24]

mov edx, DWORD PTR [rbp-12]

mov ecx, eax

sal edx, cl

mov esi, edx

mov eax, DWORD PTR [rbp-28]

mov edx, DWORD PTR [rbp-12]

mov ecx, eax

sal edx, cl

mov eax, edx

or eax, esi

mov DWORD PTR [rbp-12], eax

mov eax, DWORD PTR [rbp-20]

xor eax, DWORD PTR [rbp-12]

mov DWORD PTR [rbp-16], eax

mov eax, DWORD PTR [rbp-16]

pop rbp

ret

.LC0:

.string "Result = "

main:

push rbp

mov rbp, rsp

sub rsp, 16

mov ecx, 2

mov edx, 3

mov esi, 0

mov edi, 28

call swapBits(unsigned int, unsigned int, unsigned int, unsigned int)

mov DWORD PTR [rbp-4], eax

mov esi, OFFSET FLAT:.LC0

mov edi, OFFSET FLAT:_ZSt4cout

call std::basic_ostream<char, std::char_traits<char> >& std::operator<< <std::char_traits<char> >(std::basic_ostream<char, std::char_traits<char> >&, char const*)

mov rdx, rax

mov eax, DWORD PTR [rbp-4]

mov esi, eax

mov rdi, rdx

call std::basic_ostream<char, std::char_traits<char> >::operator<<(int)

mov eax, 0

leave

ret

__static_initialization_and_destruction_0(int, int):

push rbp

mov rbp, rsp

sub rsp, 16

mov DWORD PTR [rbp-4], edi

mov DWORD PTR [rbp-8], esi

cmp DWORD PTR [rbp-4], 1

jne .L7

cmp DWORD PTR [rbp-8], 65535

jne .L7

mov edi, OFFSET FLAT:_ZStL8__ioinit

call std::ios_base::Init::Init() [complete object constructor]

mov edx, OFFSET FLAT:__dso_handle

mov esi, OFFSET FLAT:_ZStL8__ioinit

mov edi, OFFSET FLAT:_ZNSt8ios_base4InitD1Ev

call __cxa_atexit

.L7:

nop

leave

ret

_GLOBAL__sub_I_swapBits(unsigned int, unsigned int, unsigned int, unsigned int):

push rbp

mov rbp, rsp

mov esi, 65535

mov edi, 1

call __static_initialization_and_destruction_0(int, int)

pop rbp

ret

**program to count all 1 bits in a byte stored in memory is as follows:- Label Instruction Comments LXI H 2000H; HL points at location 2000H MOV A, M; Loads A with the content of M MVI C, 08H; Sets up counter for number of bits Sets counter to count number of ones MVI B, 00H; Rotates accumulator left through carry jump2: RAL; JNC jump1; On no carry jumps to jumpl: INR B; Increases counter B by one Decreases counter C by one DCR C; jump1: JNZ jump2; When C is not zero jumps to jump2: Terminates the program HLT; **Program to swap 2 quads-words in a memory using XOR:- push rbp mov rbp, rsp

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