ridiculously fast DHGR fizzle fade

src/fx/fx.dhgr.fizzle.a

@@ -1,84 +1,58 @@
 ;license:MIT
-;(c) 2017-2020 by qkumba/4am
+;(c) 2017-2020 by qkumba/4am/John Brooks
 ;
 !cpu 6502
 !to "build/FX/DHGR.FIZZLE",plain
 *=$6000
 
-rnd1=$fe
+         ldx   #(end-start)          ; copy LFSR code to zero page
-rnd2=$ff
+-        lda   start-1, x
+         sta   $0, x
+         dex
+         bne   -
+         txa
+         tay
+         pha
+         pha
+         rts
 
-; performance notes:
+start
-; old:                    10657266..12247971 = 1590705
+!pseudopc 1 {
-; new:                    10196445..11493278 = 1296833
+; in: X,Y=0
-
+loop     txa
-         jsr   CopySelfToAuxmem
+loop1    eor   #$35                  ; LFSR form 0x3500 with period 16383
-
+         tax
-         ;init RNG
+loop2    lda   addrs, x
-
+         bpl   +
-         ldy   #1
+         and   #$7F
-         sty   rnd1
+         sta   $C003
-         dey
+         sta   $C005
-         sty   rnd2
++        sta   <dst+2
-
-         ;iterate
-
-         ldx   rnd2
-@loop
-         lda   rnd1
-@loop2
-         eor   #$ff
-         sta   $26
-         sta   $3c
-         lsr   rnd2
-         ror   rnd1
-         bcc   +
-
-         ;feedback polynomial forms #$2015 for period of 16383
-
-         lda   rnd1
-         eor   #$15
-         sta   rnd1
-         lda   rnd2
-         eor   #$20
-         sta   rnd2
-
-         ;little hack to avoid missing offset zero
-         ;screen hole at $xxFF is missed instead
-
-+        txa
-         and   #$1f
-
-         ;target page 1
-
-         ora   #$20
-         sta   $27
          eor   #$60
-         sta   $3d
+         sta   <src+2
-
+src      lda   $FD00, y
-         ;copy pixel from other page to this page
+dst      sta   $FD00, y
-
+         sta   $C002
-         cpx   #$20
+         sta   $C004
-         bcc   +
+         txa
-         sta   $c003
+         lsr
-         sta   $c005
+         tax
-+        lda   ($3c),y
+         tya
-         sta   ($26),y
+         ror
-         sta   $c002
+         tay
-         sta   $c004
+         bcc   loop2
-
+         bne   loop
-        ;exit conditions
+         bit   $C000
-
+         bmi   exit
-         ldx   rnd2
+         txa
-         bne   @loop
+         bne   loop1
-
+exit     lda   $4000                 ; last lousy byte (because LFSR never hits 0)
-         lda   $c000
+         sta   $2000
-         bmi   @exit
+         rts
-
+}
-         lda   rnd1
+end
-         cmp   #1
+addrs
-         bne   @loop2
+         !byte $20,$21,$22,$23,$24,$25,$26,$27,$28,$29,$2A,$2B,$2C,$2D,$2E,$2F
-
+         !byte $30,$31,$32,$33,$34,$35,$36,$37,$38,$39,$3A,$3B,$3C,$3D,$3E,$3F
-@exit    rts
+         !byte $A0,$A1,$A2,$A3,$A4,$A5,$A6,$A7,$A8,$A9,$AA,$AB,$AC,$AD,$AE,$AF
-
+         !byte $B0,$B1,$B2,$B3,$B4,$B5,$B6,$B7,$B8,$B9,$BA,$BB,$BC,$BD,$BE,$BF
-         !source "src/fx/fx.dhgr.common.a"