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xor not right
author
John Tsiombikas
<nuclear@member.fsf.org>
Wed, 14 Sep 2022 21:48:46 +0000
(
00:48
+0300)
committer
John Tsiombikas
<nuclear@member.fsf.org>
Wed, 14 Sep 2022 21:48:46 +0000
(
00:48
+0300)
xortest.s
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diff --git
a/xortest.s
b/xortest.s
index
b876059
..
ce89274
100644
(file)
--- a/
xortest.s
+++ b/
xortest.s
@@
-16,7
+16,7
@@
fillrest
stal $e19d00,x
inx
inx
stal $e19d00,x
inx
inx
- cpx #$300
+ cpx #$100
bne fillrest
lda #$0000
bne fillrest
lda #$0000
@@
-38,23
+38,29
@@
cmap pha
bne cmap
YVAL = 0
bne cmap
YVAL = 0
-COLIDX = 1
+TMPVAL = 1
sep #$20 ; accum 8bit
ldx #0 ; fb index
stz YVAL
sep #$20 ; accum 8bit
ldx #0 ; fb index
stz YVAL
-yloop lda YVAL
- and #$f
- sta COLIDX
+yloop ldy #0000 ; column/2 on Y reg
+xloop tya
asl
asl
+ and #$0f
+ sta TMPVAL ; save first pixel X coordinate
+ inc ; increment by 1 for the next pixel
+ eor YVAL
+ asl ; move next pixel value to high nibble
asl
asl
asl
asl
asl
asl
- ora COLIDX
- ldy #160 ; 160 bytes across
-xloop stal FB_BASE,x
+ ora TMPVAL ; first pixel X -> low nibble
+ eor YVAL
+
+ stal FB_BASE, x ; write the pixel pair
inx
inx
- dey
+ iny
+ cpy #160
bne xloop
inc YVAL
lda YVAL
bne xloop
inc YVAL
lda YVAL