dos33fsprogs/demos/second/hgr_table.s

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2023-10-17 05:19:06 +00:00
;div7_table = $b800
;mod7_table = $b900
;hposn_high = $ba00
;hposn_low = $bb00
hgr_make_tables:
;=====================
; make /7 %7 tables
;=====================
hgr_make_7_tables:
ldy #0
lda #0
ldx #0
div7_loop:
sta div7_table,Y
inx
cpx #7
bne div7_not7
clc
adc #1
ldx #0
div7_not7:
iny
bne div7_loop
ldy #0
lda #0
mod7_loop:
sta mod7_table,Y
clc
adc #1
cmp #7
bne mod7_not7
lda #0
mod7_not7:
iny
bne mod7_loop
; Hposn table
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; hposn_low, hposn_high will each be filled with $C0 bytes
; based on routine by John Brooks
; posted on comp.sys.apple2 on 2018-07-11
; https://groups.google.com/d/msg/comp.sys.apple2/v2HOfHOmeNQ/zD76fJg_BAAJ
; clobbers A,X
; preserves Y
; vmw note: version I was using based on applesoft HPOSN was ~64 bytes
; this one is 37 bytes
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build_hposn_tables:
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ldx #0
btmi:
txa
and #$F8
bpl btpl1
ora #5
btpl1:
asl
bpl btpl2
ora #5
btpl2:
asl
asl
sta hposn_low, X
txa
and #7
rol
asl hposn_low, X
rol
ora #$20
sta hposn_high, X
inx
cpx #$C0
bne btmi
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; go 16 beyond, which allows our text scrolling routine
ldx #16
extra_table_loop:
lda hposn_low,X
sta hposn_low+192,X
lda hposn_high,X
eor #$60
sta hposn_high+192,X
dex
bpl extra_table_loop
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rts