Regular Expressions in Assembly Language

Assembly language doesn’t have built-in support for regular expressions like high-level languages do. However, we can demonstrate some basic string manipulation and comparison operations that are somewhat analogous to simple pattern matching.

section .data
    str db 'peach', 0
    pattern db 'p', 'e', 'a', 'c', 'h', 0
    match_msg db 'Match found', 0
    no_match_msg db 'No match found', 0

section .text
    global _start

_start:
    ; Compare string with pattern
    mov esi, str
    mov edi, pattern
    mov ecx, 5  ; Length of string/pattern
    repe cmpsb
    
    ; Check if match was found
    jne no_match
    
    ; Print match found message
    mov eax, 4
    mov ebx, 1
    mov ecx, match_msg
    mov edx, 11
    int 0x80
    jmp exit
    
no_match:
    ; Print no match found message
    mov eax, 4
    mov ebx, 1
    mov ecx, no_match_msg
    mov edx, 14
    int 0x80
    
exit:
    ; Exit program
    mov eax, 1
    xor ebx, ebx
    int 0x80

This Assembly code demonstrates a simple string comparison, which is a basic form of pattern matching. Here’s what the code does:

1. We define a string ‘peach’ and a pattern to match against it.
2. The cmpsb instruction is used to compare the string with the pattern byte by byte.
3. If a match is found, we print “Match found”, otherwise “No match found”.

This is a very basic example and doesn’t support complex regular expression features like wildcards, character classes, or quantifiers. In practice, implementing full regular expression support in Assembly would be a complex task, typically handled by specialized libraries in higher-level languages.

To run this program, you would need to assemble it into an object file, link it, and then execute the resulting binary. The exact commands may vary depending on your system and assembler, but it might look something like this:

$ nasm -f elf64 regex.asm
$ ld -o regex regex.o
$ ./regex
Match found

Remember that Assembly language is low-level and platform-specific. This example is written for x86 assembly and may need adjustments for different architectures or operating systems.

Assembly language doesn’t have built-in regular expression libraries or high-level string manipulation functions. For complex pattern matching tasks, it’s typically more practical to use a higher-level language with built-in regex support or to interface with a regex library written in a higher-level language.