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cc65/libsrc/common/tolower.s

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;
; Ullrich von Bassewitz, 02.06.1998
;
; int tolower (int c);
;
.export _tolower
.import __ctype, __cdiff
_tolower:
tay ; Get C into Y
lda __ctype,y ; Get character classification
and #$02 ; Is this an upper case char?
beq L1 ; Jump if no
tya ; Get char back into A
sec
sbc __cdiff ; make lower case char
rts ; CC are set
L1: tya ; Get char back into A
rts ; CC are set