The subroutine that implements hexadecimal string conversion in assembly language usually needs to process each character of the string and convert it into the corresponding numerical value. The following is a simple x86 assembly language subroutine example for converting a hexadecimal string to an integer:
section .data
hex_string db "1A2F", 0 ; The hexadecimal string is null-terminated
result dd 0 ; After storage conversion integer result
section .text
global _start
_start:
; Pass the address of the hexadecimal string to the subroutine
mov esi, hex_string
call hex_to_int
; The result is stored in result, you can use it here
; ...
; Exit the program
mov eax, 1 ; System call number 1 indicates exit
xor ebx, ebx ; Return code is 0
int 0x80 ; Call the kernel
hex_to_int:
; Input: esi points to hexadecimal string
xor eax, eax ; Clear the eax register, used to store the result
xor ecx, ecx ; Clear the ecx register, used for loop counting
convert_loop:
movzx edx, byte [esi] ; Read a character in the string and extend it to 32 bits with 0
cmp dl , 0 ; If the character is null, exit the loop
je convert_done
sub dl, '0' ; Convert characters to numbers
cmp dl, 9 ; Check if it is a number between 0-9
jbe numeric_digit
sub dl, 'A' - 10 ; If it is not a number, check if it is a letter between A-F
cmp dl, 5 ; ' The ASCII code difference of characters between A' and 'F' is 5
jbe alpha_digit
sub dl, 'a' - 10 ; If it is not a capital letter, check whether it is a lowercase letter between a-f
cmp dl, 5
jbe alpha_digit
; If it is not a valid hexadecimal character, you can handle the error here or exit directly
numeric_digit:
imul eax, 16 ; Multiply the current result by 16
add eax, edx ; Add the current number to the result
jmp next_character
alpha_digit:
imul eax, 16 ; Multiply the current result by 16
add eax, edx ; Add the current number to the result
add eax, 10 ; Since it is a letter, you need to add 10
next_character:
inc esi ; Move to the next character in the string
inc ecx ; Increment the loop count
cmp ecx, 8 ; Assume the maximum length of the string is 8
jne convert_loop ; Continue loop
convert_done:
ret
Please note that this is just a simple example and may need to be adjusted based on actual needs. This code assumes that the length of the input hexadecimal string does not exceed 8 characters and is within a reasonable range. You may need to modify it to meet your needs.
