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cc65/libsrc/common/toupper.s

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;
; Ullrich von Bassewitz, 02.06.1998
;
; int toupper (int c);
;
.export _toupper
.import __ctype, __cdiff
_toupper:
tay ; Get c into Y
lda __ctype,y ; Get character classification
and #$01 ; Mask lower char bit
beq L1 ; Jump if not lower char
tya ; Get C back into A
clc
adc __cdiff ; make upper case char
rts ; CC are set
L1: tya ; Get C back
rts ; CC are set