From 39763ef7337bd8b1d118238d2b183afce2acf776 Mon Sep 17 00:00:00 2001
From: Rikard Nordgren <hrn@posteo.net>
Date: Mon, 26 Jan 2026 20:18:48 +0100
Subject: [PATCH] Update mov_MEM_FAC1 and get_FAC1_via_INDEX

---
 STATUS.md                                    | 4 ++--
 src/basic/math_mov/bba2.mov_MEM_FAC1.s       | 6 +++++-
 src/basic/math_mov/bba6.get_FAC1_via_INDEX.s | 5 +++++
 tools/similarity.c                           | 2 +-
 4 files changed, 13 insertions(+), 4 deletions(-)

diff --git a/STATUS.md b/STATUS.md
index 60c932e2..b4995691 100644
--- a/STATUS.md
+++ b/STATUS.md
@@ -221,8 +221,8 @@ Floating point mathematical routines - not official, but well known and broadly
 | `$BAFE`   | `div10_FAC1_p`         | DONE     |                                                    |
 | `$BB0F`   | `div_MEM_FAC1`         | DONE     |                                                    |
 | `$BB12`   | `div_FAC2_FAC1`        | DONE     |                                                    |
-| `$BBA2`   | `mov_MEM_FAC1`         | DONE     |                                                    |
-| `$BBA6`   | `get_FAC1_via_INDEX`   | DONE     |                                                    |
+| `$BBA2`   | `mov_MEM_FAC1`         | DONE     | From the Microsoft BASIC, original name: MOVFM     |
+| `$BBA6`   | `get_FAC1_via_INDEX`   | DONE     | From the Microsoft BASIC, no label                 |
 | `$BBC7`   | `mov_r_FAC1_TMP2`      | DONE     | From the Microsoft BASIC, original name: MOV2F     |
 | `$BBCA`   | `mov_r_FAC1_TMP1`      | DONE     | From the Microsoft BASIC, original name: MOV1F     |
 | `$BBD0`   | `mov_r_FAC1_VAR`       | DONE     | From the Microsoft BASIC, original name: MOVVF     |
diff --git a/src/basic/math_mov/bba2.mov_MEM_FAC1.s b/src/basic/math_mov/bba2.mov_MEM_FAC1.s
index 4843ff8f..0bb1bd29 100644
--- a/src/basic/math_mov/bba2.mov_MEM_FAC1.s
+++ b/src/basic/math_mov/bba2.mov_MEM_FAC1.s
@@ -3,9 +3,13 @@
 ;; #LAYOUT# *   BASIC_0 #TAKE
 ;; #LAYOUT# *   *       #IGNORE
 
+; This file is under the MIT license, it contains code released by Microsoft Corporation.
+; See LICENSE for more information.
 
 ; Math package - fetch FAC1 from RAM location
 ;
+; This is verified to be identical to the original Microsoft implementation where it was named MOVFM.
+;
 ; Input:
 ; - .A - address low byte
 ; - .Y - address high byte
@@ -24,7 +28,7 @@
 
 
 mov_MEM_FAC1:
-	sty INDEX+1
 	sta INDEX+0
+	sty INDEX+1
 
     ; FALLTHROUGH to get_FAC1_via_INDEX
diff --git a/src/basic/math_mov/bba6.get_FAC1_via_INDEX.s b/src/basic/math_mov/bba6.get_FAC1_via_INDEX.s
index cb29efa2..9bdb62b9 100644
--- a/src/basic/math_mov/bba6.get_FAC1_via_INDEX.s
+++ b/src/basic/math_mov/bba6.get_FAC1_via_INDEX.s
@@ -3,6 +3,11 @@
 ;; #LAYOUT# *   BASIC_0 #TAKE
 ;; #LAYOUT# *   *       #IGNORE
 
+; This file is under the MIT license, it contains code released by Microsoft Corporation.
+; See LICENSE for more information.
+;
+; This is verified to be identical to the original Microsoft implementation where it was part of MOVFM.
+;
 ; Math package - Mov MEM to FAC1 with address in INDEX zero page register
 ;
 ; See also:
diff --git a/tools/similarity.c b/tools/similarity.c
index f762950a..b7cc704f 100644
--- a/tools/similarity.c
+++ b/tools/similarity.c
@@ -24,7 +24,7 @@ int phase_mask[MAX_SIZE+MAX_SIZE];
 // Pairs of start, end memory addresses of known exact similarity with the open source Microsoft BASIC
 unsigned short microsoft_basic_chunks[NUM_CHUNKS * 2] = {
     0xB849, 0xB84F,
-    0xBBC7, 0xBC1A
+    0xBBA2, 0xBC1A
 };