From 908b783319872287a2e90afd0b7d66ec4dd09a6b Mon Sep 17 00:00:00 2001
From: Rikard Nordgren <hrn@posteo.net>
Date: Mon, 30 Mar 2026 21:45:54 +0200
Subject: [PATCH] Update mul_MEM_FAC1

---
 STATUS.md                                                 | 2 +-
 .../math/{ba28.mul_MEM_FAC1.jmp.s => ba28.mul_MEM_FAC1.s} | 8 +++++---
 tools/similarity.c                                        | 3 ++-
 3 files changed, 8 insertions(+), 5 deletions(-)
 rename src/basic/math/{ba28.mul_MEM_FAC1.jmp.s => ba28.mul_MEM_FAC1.s} (69%)

diff --git a/STATUS.md b/STATUS.md
index 1b8b17ef..cdb44a0f 100644
--- a/STATUS.md
+++ b/STATUS.md
@@ -219,7 +219,7 @@ Floating point mathematical routines - not official, but well known and broadly
 | `$B96F`   | `inc_FAC1`             | DONE     | From the Microsoft BASIC, original name: INCFAC    |
 | `$B983`   | `shiftr_FAC1`          | DONE     | From the Microsoft BASIC, original name: SHIFTR    |
 | `$B9EA`   | `log_FAC1`             | PARTIAL  | not fully tested yet                               |
-| `$BA28`   | `mul_MEM_FAC1`         | DONE     |                                                    |
+| `$BA28`   | `mul_MEM_FAC1`         | DONE     | From the Microsoft BASIC, original name: FMULT     |
 | `$BA2B`   | `mul_FAC2_FAC1`        | DONE     |                                                    |
 | `$BA8C`   | `mov_MEM_FAC2`         | DONE     | From the Microsoft BASIC, original name: CONUPK    |
 | `$BA90`   | `get_FAC2_via_INDEX`   | DONE     | From the Microsoft BASIC, no label                 |
diff --git a/src/basic/math/ba28.mul_MEM_FAC1.jmp.s b/src/basic/math/ba28.mul_MEM_FAC1.s
similarity index 69%
rename from src/basic/math/ba28.mul_MEM_FAC1.jmp.s
rename to src/basic/math/ba28.mul_MEM_FAC1.s
index 9c927026..bd99214f 100644
--- a/src/basic/math/ba28.mul_MEM_FAC1.jmp.s
+++ b/src/basic/math/ba28.mul_MEM_FAC1.s
@@ -3,15 +3,17 @@
 ;; #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 - multiplies FAC1 by RAM
 ;
+; This is verified to be identical to the original Microsoft implementation where it was named FMULT
+;
 ; Input:
 ; - .A - address low byte
 ; - .Y - address high byte
 ;
-; Note:
-; - C64 Wiki calls it FMULT, this looks like a mistake
 ;
 ; See also:
 ; - [CM64] Computes Mapping the Commodore 64 - page 113
diff --git a/tools/similarity.c b/tools/similarity.c
index 07bfbee6..c8a98373 100644
--- a/tools/similarity.c
+++ b/tools/similarity.c
@@ -20,13 +20,14 @@ int matches[MAX_SIZE];
 
 int phase_mask[MAX_SIZE+MAX_SIZE];
 
-#define NUM_CHUNKS 6
+#define NUM_CHUNKS 7
 // Pairs of start, end memory addresses of known exact similarity with the open source Microsoft BASIC
 unsigned short microsoft_basic_chunks[NUM_CHUNKS * 2] = {
     0xB391, 0xB39D,
     0xB3A2, 0xB3A5,
     0xB849, 0xB97D,
     0xB983, 0xB9BB,
+    0xBA28, 0xBA2A,
     0xBA8C, 0xBAB6,
     0xBB8F, 0xBCF2,
 };