Questions tagged [assembly]

An assembly language is a low-level programming language for a computer, or other programmable device, in which there is a very strong (generally one-to-one) correspondence between the language and the architecture's machine code instructions.

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Assembler for Brookshear Machine

As a small exercise in Python, I created an Assembler for the rather simple Brookshear Machine (see f.e. Brookshear Machine, please note, however, that the instruction set differs from mine). The ...
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Instant to-and-from Roman Numeral Conversion

Ⅰ Roman numerals are composed of digits taken from a small set of uppercase characters. Lowercase characters were first used in the Middle Ages. $$I,V,X,L,C,D,M$$ With these digits we can ...
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A progression of quines - follow up

This is a follow up on A progression of quines. Based on the reviews I got, I have reworked my first and fifth programs. The nice quine The answer I received from ecm made me realize that my nice ...
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Key-scanning macro in NASM Win16 against DOSBOX (Intel 8086)

Supports backspacing, but not wrapped backspacing. ...
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Multitasking in NASM Win16 Assembly

Requirements (Installed using Scoop) scoop install nasm dosbox Build (Using NASM) nasm -g tasks.asm -o tasks.com ...
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fasm convert hex byte to binary string

This fasm x64 (Linux) code seems very crude and repetitive, but it gets the job done. How could I perform this task in a more idiomatic manner? ...
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A progression of quines

A quine is a program whose only job it is to reproduce the source file that was used to create the executable in the first place. This stackoverflow post provides some reasoning about its usefulness. ...
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x64 fasm strlen

This is a simple strlen function with registers documented: ...
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Shifting bits in assembly (nasm)

I wrote a function which takes a byte and shifts the bits around. That is, there shall be the same number of 1 bits and 0 bits in the output but the bits will be shifted in position: ...
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Printing a string in NASM Win16 Assembly

A small script that simply prints a given string. It's an improved snippet that combines some recommendations given in my post on string helper functions. ...
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String helper functions in NASM Win16 Assembly

Environment NASM is required to build this program, and DosBox is required to run it. I'd recommend installing these using the Scoop Package Manager. Feel free to ignore install statements for any ...
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Ubuntu 18.04.3 ASCII strings length with embedded VT100 control codes

As my applications rely on VT-100 emulation, I found that I had to do quite a few workarounds to determine the number of visible characters in a string with embedded VT-100 control codes. So that led ...
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Cat program in x64 FASM

I wrote cat program in x64 FASM and I would like to know if there is anything that can be improved. This implementation of cat supports: Reading from stdin. Multiple arguments. I checked few cases ...
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Cat program in x86 NASM

I wrote cat program in x86 NASM and I would like to know if there is anything that can be improved. This implementation of cat ...
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Ubuntu 18.04.3 LTS get terminal columns and rows NASM

As part of the prologue of all my console applications, I need to determine the extents of the current terminal so if there are less than 132 columns or 43 lines the user can be warned output may not ...
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Display hexadecimal value stored at a register

I read a book about OS development and faced with a simple exercise: write a function that prints a hexadecimal value stored at a register. The program runs as a boot sector. I would really ...
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200 views

String routines

These are a few string routines (just the mem* ones). I've tried to optimize them the best I can without having them be too big, but I'm unsure if I've done a good ...
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Loading a file from a FAT32 filesystem in 16 bit real mode on x86 (Intel syntax assembly)

I am writing a bootloader that needs to load a file from a FAT32 filesytem. Since I need to load both the root directory first to find the start of the file, and then the actual file, I wrote a ...
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Find the maximum number in an array of numbers

The task is to find the maximum number in an array of numbers. I have taken every number in the array to be byte-sized. I have written the code such that the result is stored in ...
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Multiplying a Matrix with its Transpose

Currently, I am in the process of optimizing a MIPS assembly program that takes a n x n matrix and multiplies it with its transpose. I am trying to optimize my matrix calculation algorithm so that it ...
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Transposing a square matrix (n x n)

I wish to transpose a square matrix, permanently overwriting it. This is not the same as creating a 2nd matrix with the transposed contents of the 1st matrix. I call the procedure with 3 parameters: ...
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Brainfreeze: A Brainfuck compiler in C

BrainFreeze This is my implementation of a brainfuck compiler in C. The instruction to build/run the project (GitHub repo) can be found here. I am first converting the brainfuck source to x86 ...
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Decoding assembly instructions in a Game Boy disassembler

I am coding a game boy disassembler in C++. The program (simplified here) converts a vector of byte into an assembly instruction and print it. To do so, it iterates through the vector of bytes (char)...
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Multi-line text reader (x64 ASM)

Building upon my previous question, I have come up with a method that'll search through a buffer and return a pointer to the end of the line. The primary purpose of the function to extract rows from a ...
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Reading all file contents via x64 assembly

I have come up with the following snippet by building upon the answers given to my StackOverflow question. Just trying to get some other eyeballs to review things so that they can point out any ...
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Brainfuck to NASM compiler in Haskell

After reading this article on writing a Brainfuck interpreter in Haskell and achieving awful performance with it (for example, mandelbrot generating 37.5 minutes on an old Intel Atom powered laptop) I'...
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A simple shellcode that will kill all your processes GNU/Linux x86_64

So I made a simple shellcode that will kill all your process. Now I would like to know, can it be done in some better way? It contains 13 bytes. Thanks for all your feedback Assembly: ...
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strlen and strcmp implementation in x86 FASM assembly

I wrote my own implementation of strlen and strcmp from C in x86 FASM and I would like to know is there anything that should be changed or improved. strlen needs string in eax and is returning length ...
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Collatz Conjecture Disprover Unit - Googol Edition

The Wikipedia article about the Collatz Conjecture has these quotes: If the conjecture is false, it can only be because there is some starting number which gives rise to a sequence that does not ...
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Find some X^2 - Y^2 equal to a given Z

Request input (Z) from user, \$-65535 \leq Z \leq 65535\$. Check if \$(X^2)-(Y^2)=Z\$ (while \$0 \leq X,Y \leq 1000\$). I wrote a code which will receive Z from user, if it's negative, store the ...
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Test whether a number is a Harshad Number

A little code I wrote that will check if the entered 4-digit number is Harshad or not (Harshad number is one which divided by the sum of its digits will leave no remainder, special Harshad is the same ...
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108 views

Expand every bit into a byte

I have the following code: ...
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X86 Feature detection in preparation for Long Mode

These are the three steps that need to be taken in order to successfully activate Long Mode. Error reporting is sparse as most real hardware for developing an OS is 64 bit but probably still a good ...
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Compare two strings in extended memory - classic 8052

I'm looking for a simpler code that isn't resource hungry that can compare two strings stored in different locations in the extended memory of a classic 8052 (namely the AT89S52 microcontroller) to ...
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Swapping variable length strings asynchronously with connected microcontroller (Byte-banging)

I have an AT89S52 and an AT89C4051 microcontroller (both in the 8052 family) in which the bit lines of the data bus, one control pin and one status pin are connected together. In code, the data bus is ...
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Simple puts() function in x64 assembly

I'm trying to write as simple I/O library in x64 using linux syscalls ...
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Variadic Functions in NASM Win64 Assembly

Simple variadic function implementation in NASM Assembly. When implemented like I have below: sum.asm ...
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Tower of Hanoi in NASM Win64 Assembly

This program is an implementation of the classic puzzle Tower of Hanoi! This is my first mostly recursive Assembly program. Any advice and all topical comments on code optimization and conventions is ...
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x64 Windows Assembly - Structs in Assembly

I'm trying to code a simple person database using structs and arrays in assembly. Each person has a firstName, lastName, ...
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Guessing game in NASM Win64 Assembly

Still learning Assembly. This program is a simple guessing game to test most of the new things I've learned! Any advice and all topical comments on code optimization and conventions is appreciated! ...
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Checking if a number is prime in NASM Win64 Assembly

I'm just learning Assembly. This program is a simple attempt to determine if a given number is prime or not. Compiled as follows using VS2019 x64 Native Tools Command Prompt: ...
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gcc constant time implemenation [closed]

I need to make the following function time constant - I have already removed if statements and have written it down to one line in the loop. ...
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Main loop in assembly for a Brainfuck interpreter

I have written 2 Brainfuck interpreters, one in C++, then another in C++ with Assembly inner loop. My interpreter code can be found here (C++/ASM, requires MSVC and MASM) and here (C++). Both are ...
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Hex Dump Utility in x86-64 Assembly: Version 1.1

I recently posted a code review and received some very useful feedback. I have spent some time implementing the suggested improvements/fixes, and wish to post a follow up review, with the new and ...
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Hex Dump Utility in x86-64 Assembly, under Linux

As a relative newbie to Assembly programming, although I can get my programs to work, I have no idea if they are disastrously constructed or not. I have created a simple Hex Dump Utility, using x86-...
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Disassembler for intel 8080 v2

As many suggestions were given for the code I posted here, I decided to show you the new version for review. I Removed the OpenCatalog class, ...
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Disassembler for intel 8080

I have written a disassembler for Intel 8080, able to translate binaries into opcodes and parameters. Sorry for posting so much code, but everything posted here is useful for the understanding of the ...
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string length in x64 assembly (fasm)

Please critique this very, very basic routine which returns the length of a given char buffer or "string." ...
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MIPS Assembly Program to access elements in the 4x4 matrix, row or column-major oder

This MIPS Assembly program will make you access the elements in the 4x4 matrix in either row or column-major order i.e. accessing all elements row by row or column by column. Output is posted below ...
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Console TicTacToe implementation

I am new to assembly and I want to know how I can improve this implementation both by speed and/or binary size optimization and making code to read and support easily. Platform: Linux, x64 Assembler:...