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22 lines
538 B
ArmAsm

;
; Ullrich von Bassewitz, 02.06.1998
;
; int tolower (int c);
;
.export _tolower
.import __ctype
_tolower:
cpx #$00 ; Outside valid range?
bne L9 ; If so, return the argument unchanged
tay ; Get C into Y
lda __ctype,y ; Get character classification
lsr a
lsr a ; Get bit 1 (upper case char) into carry
tya ; Get char back into A
bcc L9 ; Jump if no upper case char
sbc #<('A'-'a') ; Make lower case char (carry already set)
L9: rts