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; Version : 1.00
; Updated : 20/8/2021
; Licence : GPLv3
; Set the case of ASCII text to upper or lower case.
default rel ; we always want this.
extern printf
%define argv0 r12
%define upper r13 ;make r13 the boolean
%define scratch r14
%define file r15
section .rodata
Usage db `%s OPTION [filename]\n Option Description\n-u Make characters uppercase.\n-l Make characters lowercase.\n`,0
OpenError: db `Could not open: %s\n`,0
section .text
global main
usage:
push rbx ;align the stack if not already done
mov rsi, [argv0] ;get argv[0]
lea rdi, [rel Usage] ;copy the usage to rdi
xor eax,eax ;al == 0 means no FP args in XMM registers
call printf wrt ..plt ;call printf with `wrt ..plt` so dynamic linking works
pop rbx ;pop rbx off the stack
mov eax, 1 ;exit with value 1
ret
stdin:
xor edi, edi ; file descriptor = stdin = 0
lea rsi, [scratch] ; buffer = address to store the bytes read
mov edx, 1 ; number of bytes to read
xor eax, eax ; syscall for read == 0
syscall
test eax, eax ; If syscall returns 0 in rax, the character is EOF
je exit ; if char is EOF: exit
call process_char
jmp stdin
process_char:
test upper,upper
jz lower ;jump to lower if upper is false
;fall through if uppercase
cmp byte[scratch],'a' ;check if read char is below 'a'
jl skip_modification ;if below 'a', it's not a lowercase char
cmp byte[scratch],'z' ;check if read char is equal to or below z
ja skip_modification ;if not equal or above, it's not a lowercase char
sub byte[scratch], 32 ;subtract 32 from ASCII char to capitalise it
jmp skip_modification ;skip lowercase
lower:
cmp byte[scratch],'A' ;check if read char is below 'A'
jl skip_modification ;if below 'A', it's not a uppercase char
cmp byte[scratch],'Z' ;check if read char is equal to or below 'Z'
ja skip_modification ;if not equal or above, it's not a lowercase char
add byte[scratch], 32 ;add 32 to ASCII char to make it lowercase
skip_modification:
mov edi, 1 ; file descriptor = stdout
lea rsi, [scratch] ; buffer = address to write to console
mov edx, 1 ; number of bytes to write
mov eax, 1 ; SYSCALL number for writing to STDOUT
syscall ; make the syscall
ret ; read the next char
file_error:
push rbx ;align the stack if not already done
mov rsi, scratch ;get argv[2]
lea rdi, [rel OpenError];copy the filename to rdi
xor eax,eax ;al == 0 means no FP args in XMM registers
call printf wrt ..plt ;call printf with `wrt ..plt` so dynamic linking works
pop rbx ;pop rbx off the stack
mov eax, 1 ;exit with value 1
ret
open_file:
add rsi, 8 ;get pointer-to-pointer to argv[2]
mov scratch,[rsi] ;get pointer to argv[2] and copy it to scratch
mov eax, 2 ;syscall sys_open
mov rdi, scratch ;place pointer to filename string in rdi
xor esi, esi ;O_RDONLY
xor edx, edx ;don't need a mode
syscall
test eax, eax
js file_error ;if nonzero, sys_open failed
mov file, rax ;store fp in file
read_file:
mov rdi, file ;file descriptor = rax from sys_open above
lea rsi, [scratch] ;read into scratch
mov edx, 1 ;number of bytes to read
xor eax, eax ;syscall for read == 0
syscall
test eax, eax ;If syscall returns 0 in rax, the character is EOF
je close_file ;if char is EOF, close the file and exit
call process_char
jmp read_file
main:
mov argv0, rsi ;save argv[0] for later
cmp edi, 2
jl usage ;show usage if not enough args are provided
check_args:
add rsi, 8 ;get pointer-to-pointer to argv[1]
mov scratch, [rsi] ;get pointer to argv[1] and copy it to scratch
cmp byte[scratch], '-'
jne usage ;show usage if there is no argument (missing -)
xor upper, upper ;assume lowercase by default
cmp byte[scratch+1], 'u'
jne false ;fall through if argv[1][1] == 'u' and thus set upper boolean to true
mov upper,1
false:
cmp edi, 3
jl stdin ;go to stdin mode if no filename is provided
jg usage ;go to usage if more that 3 args are provided
jmp open_file ;jump to file opening
close_file:
mov rdi, file ;fp to close
mov eax, 3 ;sys_close
syscall
exit:
xor eax, eax
ret
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