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cc65/libsrc/atari/clrscr.s

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;
; Christian Groessler, Apr-2000
;
; void clrscr (void);
;
.export _clrscr
.include "atari.inc"
.ifdef DIRECT_SCREEN
.importzp ptr1
_clrscr:lda SAVMSC ; screen memory
sta ptr1
lda SAVMSC+1
clc
adc #>(40*24)
sta ptr1+1
lda #0 ; screen code of space char
ldy #<(40*24) ; 40x24: size of default atari screen
ldx #>(40*24)
_clr1: sta (ptr1),y
dey
bne _clr1
sta (ptr1),y
dex
bmi done
ldy ptr1+1
dey
sty ptr1+1
ldy #255
jmp _clr1
done: sta COLCRS
sta ROWCRS
rts
.else
.import putchar
_clrscr:
lda #ATCLR
jmp putchar
.endif