From 7746f34350e46f6d508aac3f99d47d8f232c42f2 Mon Sep 17 00:00:00 2001
From: "B. Watson" <urchlay@slackware.uk>
Date: Sat, 5 Nov 2022 01:43:36 -0400
Subject: Save ~15 cycles in drunkwalk.

---
 dla.s | 29 +++++++++++++----------------
 1 file changed, 13 insertions(+), 16 deletions(-)

diff --git a/dla.s b/dla.s
index fc5bdea..4a30921 100644
--- a/dla.s
+++ b/dla.s
@@ -511,41 +511,38 @@ drunkwalk:
  ldx part_x ;3
  ; using bit/bmi/bvc saves 5.25 cycles on average, compared to
  ; immediate cmp and bne.
- ; 4 code paths: up=16, down=17, left=15, right=13, avg=15.25.
+ ; 4 code paths: up=15, down=18, left=19, right=17, avg=17.25.
  ; note that part_x and part_y are *never* zero; all the bne's here
  ; are "branch always".
+ ; all the "cmp #0" here get their operands modified by set_limits.
 dwloop:
  ldy part_y
  bit RANDOM ;4 ; use top 2 bits (probably more random, definitely faster)
  bmi lr     ;2/3
  bvc down   ;2/3
  dey        ;2 ; N=1 V=1 up
- bne checkbounds ;3
+selfmod_ymin = * + 1
+ cpy #0               ; 2
+ beq oob              ; 2
+ bne checkneigh ;3
 down:
  iny        ;2 ; N=1 V=0 down
- bne checkbounds ;3
+selfmod_ymax = * + 1
+ cpy #0               ; 2
+ beq oob              ; 2
+ bne checkneigh ;3
 lr:
  bvc right  ;2/3
  dex        ;3 ; N=0 V=1 left
- bne checkbounds ;3
-right:
- inx        ;3 ; N=0 V=0 right
-
-checkbounds:
- ; all the "cmp #0" here get their operands modified by set_limits.
 selfmod_xmin = * + 1
  cpx #0               ; 2
  beq oob              ; 2
+ bne checkneigh ;3
+right:
+ inx        ;3 ; N=0 V=0 right
 selfmod_xmax = * + 1
  cpx #0               ; 2
  beq oob              ; 2
-selfmod_ymin = * + 1
- cpy #0               ; 2
- beq oob              ; 2
-selfmod_ymax = * + 1
- cpy #0               ; 2
- beq oob              ; 2
- ; checkbounds is 16 cycles when the pixel is in bounds.
 
 checkneigh:
  ; check neighbors. used to be a subroutine, inlined it.
-- 
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