libx64asm-atoi-itoa

An x86-64 assembly library for converting integers to ASCII (itoa64) and ASCII to integers (atoi64). Supports signed 64-bit integers (positive and negative). Can be used in Linux programs, bootloaders, or kernels.

Features

• Convert signed 64-bit integers → ASCII (itoa64)
• Convert ASCII → signed 64-bit integers (atoi64)
• Null-terminated strings
• Minimal and fast
• Works on major Linux distributions

Files

• src/atoi64.asm — ASCII → integer
• src/itoa64.asm — integer → ASCII
• setup.sh — installs NASM if missing and builds .o files
• build/ — folder for assembled object files

Architecture:

• amd64 (x86_64, 64-bit)

Platform:

• Linux only

Clone the Repository

Clone the repository first:

git clone https://github.com/s-r-e-e-r-a-j/libx64asm-atoi-itoa.git

Navigate to the project directory:

cd libx64asm-atoi-itoa

After cloning and navigating to the project directory, follow the Build Instructions section.

Build Instructions

Make setup.sh executable and run it:

chmod +x setup.sh
./setup.sh

• Installs NASM if missing (supports Debian, RHEL, Arch)
• Assembles atoi64.asm and itoa64.asm into .o files in build/
• After running setup.sh, the object files for the library will be in the build/ folder.
• You will need to link the .o files in the build/ folder when compiling your own programs.

Functions

atoi64

• Input:
  • RDI → pointer to null-terminated ASCII string
• Output:
  • RAX → signed 64-bit integer

itoa64

• Input:
  • RDI → signed 64-bit integer
  • RSI → pointer to output buffer
• Output:
  • RAX → string length (without null byte)
  • Output buffer is null-terminated

Linking with the Library

After running setup.sh, the library object files are created in the build/ folder:

build/atoi64.o
build/itoa64.o

When you build your own program, you must link these object files.

Example

nasm -f elf64 main.asm -o main.o
ld -o main main.o build/atoi64.o build/itoa64.o -e _start

If your program is in another directory Use the path to the build/ folder:

nasm -f elf64 main.asm -o main.o
ld -o main main.o \
../libx64asm-atoi-itoa/build/atoi64.o \
../libx64asm-atoi-itoa/build/itoa64.o \
-e _start

Important

• The library is not installed system-wide
• Only the .o files in build/ are needed
• Always include them when linking

Linking Only What You Use

You only need to link the object file for the function you use.

• If you use atoi64 only, link atoi64.o
• If you use itoa64 only, link itoa64.o
• If you use both, link both files

Examples

Using only atoi64:

ld -o program program.o build/atoi64.o -e _start

Using only itoa64:

ld -o program program.o build/itoa64.o -e _start

Using both:

ld -o program program.o build/atoi64.o build/itoa64.o -e _start

From another directory

ld -o program program.o \
../libx64asm-atoi-itoa/build/atoi64.o \
-e _start

or

ld -o program program.o \
../libx64asm-atoi-itoa/build/itoa64.o \
-e _start

Example: atoi64

global _start
extern atoi64

section .data
    input db "-12345", 0 ; input string

section .text
_start:
    mov rdi, input ; string address
    call atoi64 ; convert to number

    ; rax now holds the result

    mov rax, 60 ; exit syscall
    xor rdi, rdi ; exit code 0
    syscall

Build:

nasm -f elf64 example_atoi.asm -o example_atoi.o
ld -o example_atoi example_atoi.o build/atoi64.o -e _start

Example: itoa64

global _start
extern itoa64

section .bss
    buffer resb 32  ; output buffer

section .text
_start:
    mov rdi, -9876  ; number to convert
    mov rsi, buffer ; buffer address
    call itoa64 ; convert to string

; RAX = length of string (excluding null byte)

; buffer now has the text

    mov rax, 60 ; exit syscall
    xor rdi, rdi ; exit code 0
    syscall

Build:

nasm -f elf64 example_itoa.asm -o example_itoa.o
ld -o example_itoa example_itoa.o build/itoa64.o -e _start

License

This project is licensed under the MIT License