From a485abfc773b249f8181cf5b5410ab3cb8b10197 Mon Sep 17 00:00:00 2001
From: Bobbi Webber-Manners <bobbi.manners@gmail.com>
Date: Tue, 21 Sep 2021 17:02:20 -0400
Subject: [PATCH] Faster and smaller coordinate conversion (thx @xot)

---
 applecorn.po | Bin 819200 -> 819200 bytes
 auxmem.gfx.s | 127 +++++++++++++++++++--------------------------------
 2 files changed, 47 insertions(+), 80 deletions(-)

diff --git a/applecorn.po b/applecorn.po
index 974163d2227d0bec928a5730c969d1bb95da4ea0..cad9bc6423bfc3342d862dec17e8012815261d46 100644
GIT binary patch
delta 2600
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diff --git a/auxmem.gfx.s b/auxmem.gfx.s
index d129dc5..62e0726 100644
--- a/auxmem.gfx.s
+++ b/auxmem.gfx.s
@@ -6,94 +6,61 @@
 * Convert high-resolution screen coordinates
 * from 1280x1024 to 280x192
 CVTCOORD
-* X-coordinate in VDUQ+5,+6   1280/4*7/8=280
-            LDA   VDUQ+5         ; X-coord -> ZP1 and ZP2
-            STA   ZP1+0
-            STA   ZP2+0
-            LDA   VDUQ+6
+* X-coordinate in VDUQ+5,+6   1280*7/32=280
+            LDA   VDUQ+6        ; X-coord -> ZP1 and ZP2
             STA   ZP1+1
             STA   ZP2+1
-            CLC                  ; ZP1 divide by 2 (0-639 now)
-            ROR   ZP1+1
-            ROR   ZP1+0
-            CLC                  ; ZP1 divide by 2 (0-319 now)
-            ROR   ZP1+1
-            ROR   ZP1+0
-            CLC                  ; ZP1+ZP2->ZP2
-            LDA   ZP1+0
-            ADC   ZP2+0
+            LDA   VDUQ+5
+            STA   ZP1+0
+            ASL   A             ; ZP2 *= 8
+            ROL   ZP2+1
+            ASL   A
+            ROL   ZP2+1
+            ASL   A
+            ROL   ZP2+1
+            SEC                 ; ZP2-ZP1->ZP2
+            SBC   ZP1+0
             STA   ZP2+0
-            LDA   ZP1+1
-            ADC   ZP2+1
-            STA   ZP2+1
-            CLC                  ; ZP1+ZP2->ZP2
-            LDA   ZP1+0
-            ADC   ZP2+0
-            STA   ZP2+0
-            LDA   ZP1+1
-            ADC   ZP2+1
-            STA   ZP2+1
-            CLC                  ; ZP1+ZP2->ZP2
-            LDA   ZP1+0
-            ADC   ZP2+0
-            STA   ZP2+0
-            LDA   ZP1+1
-            ADC   ZP2+1
-            STA   ZP2+1
-            CLC                  ; ZP2 divide by 2
-            ROR   ZP2+1
-            ROR   ZP2+0
-            CLC                  ; ZP2 divide by 2
-            ROR   ZP2+1
-            ROR   ZP2+0
-            CLC                  ; ZP2 divide by 2
-            ROR   ZP2+1
-            ROR   ZP2+0
-            LDA   ZP2+0
-            STA   VDUQ+5
             LDA   ZP2+1
-            STA   VDUQ+6
-
-* Y-coordinate in VDUQ+7,+8   1024/4*3/4=192
-            LDA   VDUQ+7         ; Y-coord -> ZP1
-            STA   ZP1+0
-            LDA   VDUQ+8
-            STA   ZP1+1
-            CLC                  ; ZP1 divide by 2 (0-512 now)
-            ROR   ZP1+1
-            ROR   ZP1+0
-            CLC                  ; ZP1 divide by 2 (0-256 now)
-            ROR   ZP1+1
-            ROR   ZP1+0
-            LDA   ZP1+0          ; Copy ZP1->ZP2
-            STA   ZP2+0
-            LDA   ZP1+1
-            STA   ZP2+1
-            CLC                  ; ZP1+ZP2->ZP2
-            LDA   ZP1+0
-            ADC   ZP2+0
-            STA   ZP2+0
-            LDA   ZP1+1
-            ADC   ZP2+1
-            STA   ZP2+1
-            CLC                  ; ZP1+ZP2->ZP2
-            LDA   ZP1+0
-            ADC   ZP2+0
-            STA   ZP2+0
-            LDA   ZP1+1
-            ADC   ZP2+1
-            STA   ZP2+1
-            CLC                  ; ZP2 divide by 2
-            ROR   ZP2+1
+            SBC   ZP1+1
+            LSR   A             ; ZP2 /= 32
             ROR   ZP2+0
-            CLC                  ; ZP2 divide by 2
-            ROR   ZP2+1
+            LSR   A
             ROR   ZP2+0
+            LSR   A
+            ROR   ZP2+0
+            LSR   A
+            ROR   ZP2+0
+            LSR   A
+            ROR   ZP2+0
+            STA   VDUQ+6        ; ZP2 -> X-coord
             LDA   ZP2+0
+            STA   VDUQ+5    
+
+* Y-coordinate in VDUQ+7,+8   1024*3/16=192
+            LDA   VDUQ+8         ; Y-coord -> ZP1
+            STA   ZP1+1
+            STA   ZP2+1
+            LDA   VDUQ+7
+            STA   ZP1+0
+            ASL   A              ; ZP2 *= 2
+            ROL   ZP2+1
+            CLC                  ; ZP2+ZP1->ZP2
+            ADC   ZP1+0
+            STA   ZP2+0
+            LDA   ZP2+1
+            ADC   ZP1+1
+            LSR   A             ; ZP2 /= 16
+            ROR   ZP2+0
+            LSR   A
+            ROR   ZP2+0
+            LSR   A
+            ROR   ZP2+0
+            LSR   A
+            STA   VDUQ+8        ; ZP2 -> Y-coord
+            LDA   ZP2+0
+            ROR
             STA   VDUQ+7
-            LDA   ZP2+1
-            STA   VDUQ+8
-
             RTS
 
 * Add coordinates to XPIXEL, YPIXEL