fox32rom/string.asm

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NASM
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2022-04-24 07:31:44 +02:00
; string copy/compare routines
2022-04-24 01:47:17 +02:00
; copy string from source pointer to destination pointer
; if the source and destination overlap, the behavior is undefined
; inputs:
; r0: pointer to source
; r1: pointer to destinaton
; outputs:
; none
copy_string:
push r0
push r1
push r2
copy_string_loop:
mov.8 r2, [r0]
mov.8 [r1], r2
inc r0
inc r1
cmp.8 r2, 0
ifnz jmp copy_string_loop
pop r2
pop r1
pop r0
ret
2022-04-24 07:31:44 +02:00
; compare string from source pointer with destination pointer
; inputs:
; r0: pointer to source
; r1: pointer to destinaton
; outputs:
; Z flag
compare_string:
push r0
push r1
compare_string_loop:
; check if the strings match
cmp.8 [r0], [r1]
ifnz jmp compare_string_not_equal
; if this is the end of string 1, then this must also be the end of string 2
; the cmp above alredy ensured that both strings have a null-terminator here
cmp.8 [r0], 0
ifz jmp compare_string_equal
inc r0
inc r1
jmp compare_string_loop
compare_string_not_equal:
; Z flag is already cleared at this point
pop r1
pop r0
ret
compare_string_equal:
; set Z flag
mov r0, 0
cmp r0, 0
pop r1
pop r0
ret
2022-05-02 02:59:54 +02:00
; get the length of a string
; inputs:
; r0: pointer to null-terminated string
; outputs:
; r0: length of the string, not including the null-terminator
string_length:
push r1
mov r1, 0
string_length_loop:
; check if this is the end of the string
cmp.8 [r0], 0
ifz jmp string_length_end
inc r0
inc r1
jmp string_length_loop
string_length_end:
mov r0, r1
pop r1
ret