101 lines
5.7 KiB
NASM
101 lines
5.7 KiB
NASM
bits 32 ; assembling for the 32 bits architecture
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; declare the EntryPoint (a label defining the very first instruction of the program)
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global start
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; declare external functions needed by our program
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extern exit,fopen,fprintf,fscanf,fread,fwrite,remove,rename,fclose
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import exit msvcrt.dll ; exit is a function that terminates the program. It is defined in msvcrt.dll
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import fopen msvcrt.dll ; fopen is a function that opens a file. It is defined in msvcrt.dll
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import fprintf msvcrt.dll ; fprintf is a function that prints a formatted string to a file. It is defined in msvcrt.dll
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import fscanf msvcrt.dll ; fscanf is a function that reads a formatted string from a file. It is defined in msvcrt.dll
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import fread msvcrt.dll ; fread is a function that reads a block of data from a file. It is defined in msvcrt.dll
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import fwrite msvcrt.dll ; fwrite is a function that writes a block of data to a file. It is defined in msvcrt.dll
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import remove msvcrt.dll ; remove is a function that deletes a file. It is defined in msvcrt.dll
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import rename msvcrt.dll ; rename is a function that renames a file. It is defined in msvcrt.dll
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import fclose msvcrt.dll ; fclose is a function that closes a file. It is defined in msvcrt.dll
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; our data is declared here (the variables needed by our program)
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segment data use32 class=data
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; ...
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file_path_read db "a.txt", 0 ; the path to the file we want to open
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file_path_write db "b.txt", 0 ; the path to the file we want to open
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access_mode_read db "r", 0 ; the access mode we want to use when opening the file
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access_mode_write db "w", 0 ; the access mode we want to use when opening the file
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file_read dd 0 ; the file pointer returned by fopen
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file_write dd 0 ; the file pointer returned by fopen
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read_value dd 0 ; the value read from the file
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; our code starts here
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segment code use32 class=code
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start:
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; ...
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; open the file
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push dword access_mode_read ; push the parameter for fopen onto the stack
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push dword file_path_read ; push the parameter for fopen onto the stack
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call [fopen] ; call fopen to open the file
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add esp, 4*2 ; remove the parameters from the stack
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cmp eax, 0 ; compare the return value of fopen with 0
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jz exit_label ; if fopen returned 0, then the file could not be opened, so we exit_label the program
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mov [file_read], eax ; save the file pointer returned by fopen in the variable file
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push dword access_mode_write ; push the parameter for fopen onto the stack
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push dword file_path_write ; push the parameter for fopen onto the stack
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call [fopen] ; call fopen to open the file
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add esp, 4*2 ; remove the parameters from the stack
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cmp eax, 0 ; compare the return value of fopen with 0
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jz exit_label ; if fopen returned 0, then the file could not be opened, so we exit_label the program
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mov [file_write], eax ; save the file pointer returned by fopen in the variable file
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; read the file
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loop_label:
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push dword [file_read] ; push the parameter for fread onto the stack
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push dword 1 ; push the parameter for fread onto the stack
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push dword 1 ; push the parameter for fread onto the stack
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push dword read_value ; push the parameter for fread onto the stack
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call [fread] ; call fread to read the file
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add esp, 4*4 ; remove the parameters from the stack
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cmp eax, 0 ; compare the return value of fread with 0
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jz end ; if fread returned 0, then the file could not be read, so we exit_label the program
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inc byte [read_value] ; increment the value read from the file
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push dword [file_write] ; push the parameter for fwrite onto the stack
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push dword 1 ; push the parameter for fwrite onto the stack
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push dword 1 ; push the parameter for fwrite onto the stack
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push dword read_value ; push the parameter for fwrite onto the stack
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call [fwrite] ; call fwrite to write the file
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add esp, 4*4 ; remove the parameters from the stack
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cmp eax, 0 ; compare the return value of fwrite with 0
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jz exit_label ; if fwrite returned 0, then the file could not be written, so we exit_label the program
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jmp loop_label
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end:
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; close the file
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push dword [file_read] ; push the parameter for fclose onto the stack
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call [fclose] ; call fclose to close the file
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add esp, 4 ; remove the parameter from the stack
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push dword [file_write] ; push the parameter for fclose onto the stack
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call [fclose] ; call fclose to close the file
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add esp, 4 ; remove the parameter from the stack
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;remove a.txt file
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push dword file_path_read ; push the parameter for remove onto the stack
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call [remove] ; call remove to remove the file
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add esp, 4 ; remove the parameter from the stack
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;rename b.txt to a.txt
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push dword file_path_read ; push the parameter for rename onto the stack
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push dword file_path_write ; push the parameter for rename onto the stack
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call [rename] ; call rename to rename the file
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add esp, 4*2 ; remove the parameters from the stack
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exit_label:
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push dword 0 ; push the parameter for exit_label onto the stack
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call [exit] ; call exit_label to terminate the program
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