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cc65/libsrc/common/zerobss.s

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;
; Ullrich von Bassewitz, 1998-09-17, 2005-02-26.
;
; Zero the bss segment.
;
.export zerobss
.import __BSS_RUN__, __BSS_SIZE__
.importzp ptr1
.segment "INIT"
zerobss:
lda #<__BSS_RUN__
sta ptr1
lda #>__BSS_RUN__
sta ptr1+1
lda #0
tay
; Clear full pages
L1: ldx #>__BSS_SIZE__
beq L3
L2: sta (ptr1),y
iny
bne L2
inc ptr1+1
dex
bne L2
; Clear remaining page (y is zero on entry)
L3: cpy #<__BSS_SIZE__
beq L4
sta (ptr1),y
iny
bne L3
; Done
L4: rts