From 25a8d7b49734fb8dbcd559cb6ab39ad0b99e3a57 Mon Sep 17 00:00:00 2001
From: Vince Weaver <vincent.weaver@maine.edu>
Date: Thu, 31 May 2018 12:47:28 -0400
Subject: [PATCH] entropy: shave another byte off thanks to Nick Westgate

---
 two-liners/README.entropy |   2 +-
 two-liners/entropy.dsk    | Bin 143360 -> 143360 bytes
 two-liners/entropy.s      |  22 ++++++++++++++--------
 3 files changed, 15 insertions(+), 9 deletions(-)

diff --git a/two-liners/README.entropy b/two-liners/README.entropy
index aa03cdb1..726c5554 100644
--- a/two-liners/README.entropy
+++ b/two-liners/README.entropy
@@ -52,7 +52,7 @@ This sound simple, but it leads to some neat patterns.
 =======================
 
 I thought it would be neat to see how small I could make this in assembly
-language. Currently I have it down to 119 bytes (the executable is 123
+language. Currently I have it down to 118 bytes (the executable is 122
 bytes because DOS33 includes size/address filesystem metadata in the file
 itself).
 
diff --git a/two-liners/entropy.dsk b/two-liners/entropy.dsk
index ec237394a8703bd65f5ae4cebe5b4a42ee866aa8..dfb654a028677e8b4daceca4258497a27c178e9d 100644
GIT binary patch
delta 90
zcmV-g0Hyzc;0S==2!ON!9xeegw;wJ6;{p|W03g`&q6miksRT%=1cm*g0EYhPml!bt
wHUV&#PcZ=%8nS3<1<AdTqNe=l;17_Ou#gfzBqS{@Ha0(#0Sb?|3^D=q{ZafQ=l}o!

delta 107
zcmV-x0F?iL;0S==2!ON!9xeeew;wJ6;{q0Z03g`&sR)JqsRT%=1cm*n0EPad0hbps
z0X8vmpbV)1AYJyQ{TOKmh5gV1=KjeT(6MM~1<AdTq2~Oh{K*fHm#~f!KO`hAEjBhk
NlK~2iw+u1?^!;<ZE>Hjf

diff --git a/two-liners/entropy.s b/two-liners/entropy.s
index ecffaa09..a33fdbef 100644
--- a/two-liners/entropy.s
+++ b/two-liners/entropy.s
@@ -2,7 +2,7 @@
 ; by Dave McKellar of Toronto
 ; Two-line BASIC program
 ; Found on Beagle Brother's Apple Mechanic Disk
-; Converted to 6502 Assembly by Vince Weaver
+; Converted to 6502 Assembly by Deater (Vince Weaver) vince@deater.net
 
 ; 24001	ROT=0:FOR I=1 TO 15: READ A,B: POKE A,B: NEXT: DATA
 ;	232,252,233,29,7676,1,7678,4,7679,0,7680,18,7681,63,
@@ -26,9 +26,12 @@
 ;	126 bytes:	nextx: simplify by using knowledge of possible x/y vals
 ;	124 bytes:	qkumba noticed we can bump yloop up to include the
 ;			pha, letting us remove two now unneeded stack ops
-;	123 byts:	qkumba noticed XDRAW0 always exits with X==0 so
+;	123 bytes:	qkumba noticed XDRAW0 always exits with X==0 so
 ;			we can move some things to use X instead and
 ;			can get a "1" value simply by using INX
+;	122 bytes:	Nick Westgate noticed that we could save a byte
+;			in eloop by pushing the stx ELOOP to the beginning
+;			rather than the end.
 
 ;BLT=BCC, BGE=BCS
 
@@ -69,11 +72,14 @@ XDRAW0		=	$F65D
 entropy:
 
 	jsr	HGR2		; Hi-res graphics, no text at bottom
+				; Y=0, A=$60 after this call
 
-	lda	#8		; Unlike the BASIC, our loop is *100
-	sta	EPOS		; 8 to 15 rather than .08 to .15
-
+	ldx	#8		; Unlike the BASIC, our loop is *100
+				; 8 to 15 rather than .08 to .15
 eloop:
+	stx	EPOS		; EPOS was temporarily in X
+
+
 	lda	#4		; FOR Y=4 to 189 STEP 6
 yloop:
 	pha			; YPOS stored on stack
@@ -196,9 +202,9 @@ nexty:				; NEXT Y
 	bcc	yloop		; if so, loop
 
 nexte:				; NEXT E
-	inc	EPOS
-	lda	EPOS
-	cmp	#15
+	ldx	EPOS
+	inx			; EPOS saved at beginning og eloop
+	cpx	#15
 	bcc	eloop		; branch if <15
 
 	bcs	entropy