Questions tagged [x86]

Code which runs on any of the x86 family of instruction set architectures. Questions should also be tagged for the source language (typically [assembly], though others are possible).

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5
votes
2answers
111 views

Sobel Operator - SIMD x86 Intrinsics Implementation

I'm learning C# .NET 5 Intrinsics and interested in best practices. It's really hard now to find enough information about how SIMD instructions (logically/internally) work in .NET. In addition i'm not ...
6
votes
0answers
137 views

Optimizing bit-matching performance using AVX compiler intrinsic

We are working on a complicated math problem, very detailed question with description of the problem is here: C++ multi-threaded determination of curling numbers in vectors. That code is now converted ...
24
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4answers
2k views

x86-64 Assembly - Sum of multiples of 3 or 5

I'm trying to learn some basic x86 assembly and so I've begun solving Project Euler problems. I was hoping for some critique of my code that, hopefully, includes either the efficiency of the ...
3
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2answers
129 views

Very simple OS in Assembly

I made a very simple OS in Assembly. But my code is too long. I want to make my code shorter. Here is my code: ...
5
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1answer
72 views

Find all the digits in a string

S is a given character string, then I have to find all the digits characters of S. Did I make it unnecessarily complicated? <...
6
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1answer
76 views

Given a byte string S of length l, obtain the string D of length l-1 as D(i) = S(i) * S(i+1)

Given a byte string S of length l, obtain the string D of length l-1 as D(i) = S(i) * S(i+1) (each element of D is the product of two consecutive elements of S). ...
4
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2answers
97 views

x86_64 nasm criticism on malloc and free implementation

I have made my own malloc implementation using this resource as a guide https://danluu.com/malloc-tutorial/ I was hoping to receive some feed back on how I can improve upon it, and If I did any major ...
7
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1answer
82 views

x / 2 + 100 * (a + b) - 3 / (c + d) + e * e in assembly

write an algorithm for: x / 2 + 100 * (a + b) - 3 / (c + d) + e * e knowing that: a, c - word, b, d - byte, e - doubleword, x - qword ...
1
vote
1answer
52 views

Criticism on x86_64 nasm printBigInt and bigPow implementation

The first "method" I have coded is _bigPow which can pow(x, y) on any number which is really big. And the _printBigInt prints a very big integer. Plus I have tried to comment most parts of ...
3
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0answers
51 views

Printing a decimal number as a string

I've written a short script to print a number to a string. This actually was very difficult for me to do -- I'm not sure if this is actually a tricky task or just because I'm so new to asm I was ...
4
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1answer
62 views

Print a list of strings in assembly

How does the following program look to print a list of strings? What places can I improve? Are there easier ways to print something like a linebreak after each string rather than hardcoding the ...
2
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1answer
61 views

Program to find the maximum number/factor in a list

I have written the following basic assembly program to find the maximum number in a list divisible by a number. Here is what I have thus far: ...
2
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1answer
62 views

x86 program to do an exponent

For continuity, my last question was with adding numbers together with a function call: Example x86-64 program. In this one I've tried to apply the lessons pointed out in the previous answer (stack ...
4
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2answers
83 views

Criticism on x86_64 nasm assembly strToInt and printInt implementation

I am pretty new to assembly I would like criticism on two "methods" I have written. One converts string to int and the other prints an int to stdout. Any advise helps out. ...
3
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1answer
79 views

Example x86-64 program

I wrote the following x86 program to make sure I'm following the correct practices in calling a function and then exiting to the OS: ...
3
votes
1answer
134 views

Simple input and output in assembly x86_64

I am new assembly programming in Linux (x86_64) and I want to make sure that I am programing in a correct way. I wrote a program that just takes an input from the user and then writes his input to ...
7
votes
1answer
87 views

Project Euler #1 AT&T Assembly

To practice learning x64 AT&T Assembly (GAS), I implemented three solutions for Project Euler Problem 1 (find the sum of all the multiples of 3 or 5 below 1000). The codes and a rough pseudocode ...
4
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1answer
99 views

Selection sort algorithm in x86_64 Yasm assembler

I returned to study assembly language. And this is actually my first function written in Yasm. Implementing this function is a suggested project from this book. I slightly modified the pseudo code ...
3
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1answer
57 views

A very fast Game of Life

The rules of John Conway's Game of Life are simple: An OFF pixel that has 3 live neighbours is turned ON. An ON pixel that has anything other than 2 or 3 live neighbours is turned OFF. Many people ...
5
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2answers
130 views

x86 Single Stage Bootloader

I'm learning OS development and have written a single stage bootloader that loads the kernel, enters to protected mode and finally jumps to the kernel. I'll very appreciate any feedback and ...
4
votes
1answer
47 views

A fast generator of palindrome dates in chronological order

02/02/2020 is a palindrome day because reading the date left-to-right or right-to-left still refers to the same calendar date. And because it doesn't matter whether you use the DD/MM/YYYY format or ...
5
votes
1answer
127 views

Program for string length in x86

It takes in a string from the command line. prints out the length of the string. I'm mostly looking for tips and general convention suggestions But I'm open to any other criticism also. Roast it ...
3
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0answers
44 views

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 represent ...
5
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2answers
37 views

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 ...
9
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2answers
115 views

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. ...
3
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1answer
45 views

x64 fasm strlen

This is a simple strlen function with registers documented: ...
1
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1answer
283 views

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: ...
6
votes
1answer
164 views

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 ...
7
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4answers
93 views

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 ...
5
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2answers
144 views

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 ...
7
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3answers
212 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 ...
13
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1answer
315 views

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 ...
5
votes
2answers
109 views

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 ...
3
votes
1answer
66 views

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: ...
-3
votes
2answers
458 views

Converting Array of `Float32` (`float`) to Array of `UINT8` (`unsigned char`) Using AVX2 [closed]

Given input array of Float32 (float) with numElements how could one efficiently convert it ...
0
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1answer
216 views

Converting Array of `UINT8` (`unsigned char`) to Array of `Float32` (`float`) Using AVX2

Given input array of UINT8 (unsigned char) with numElements how could one efficiently ...
1
vote
0answers
80 views

No performance gain with SIMD 3D vector for ray tracer

I wrote two versions of vector class for my ray tracer. Non-SIMD version and SIMD version. You can find the code below. I want to ask what things should I keep in mind to get max performance with SIMD....
3
votes
1answer
91 views

Generating random number from a binomial distribution

In my application of Monte Carlo simulation, the crucial part is to generate a random number from a binomial distribution with parameters n = size and p = 0.5. Here is my current implementation ...
3
votes
1answer
898 views

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 ...
4
votes
3answers
223 views

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: ...
6
votes
3answers
5k views

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 ...
5
votes
1answer
102 views

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 ...
6
votes
4answers
387 views

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 ...
4
votes
2answers
179 views

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 ...
4
votes
1answer
124 views

Expand every bit into a byte

I have the following code: ...
7
votes
1answer
58 views

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 ...
3
votes
3answers
2k views

Simple puts() function in x64 assembly

I'm trying to write as simple I/O library in x64 using linux syscalls ...
4
votes
1answer
231 views

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 ...
4
votes
1answer
525 views

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 ...
7
votes
2answers
605 views

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-...