Update sub_MEM_FAC1

STATUS.md

@@ -205,7 +205,7 @@ Floating point mathematical routines - not official, but well known and broadly
 | `$B7B5`   | `STRVAL`               | PARTIAL  | Only for 38k memory model                          |
 | `$B7F7`   | `convert_FAC1_to_ADDR` | NOT DONE |                                                    |
 | `$B849`   | `add_HALF_FAC1`        | DONE     | From the Microsoft BASIC, original name: FADDH     |
-| `$B850`   | `sub_MEM_FAC1`         | DONE     |                                                    |
+| `$B850`   | `sub_MEM_FAC1`         | DONE     | From the Microsoft BASIC, original name: FSUB      |
 | `$B853`   | `sub_FAC2_FAC1`        | DONE     |                                                    |
 | `$B862`   | `add_align_exponents`  | DONE     |                                                    |
 | `$B867`   | `add_MEM_FAC1`         | DONE     |                                                    |

src/basic/math/b850.sub_MEM_FAC1.s

@@ -3,13 +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 - subtract FAC1 from memory variable
 ;
 ; Input:
 ; - .A - address low byte
 ; - .Y - address high byte
 ;
+; This is verified to be identical to the original Microsoft implementation where it was named FSUB.
+;
 ; See also:
 ; - [CM64] Computes Mapping the Commodore 64 - page 112
 ; - https://www.c64-wiki.com/wiki/Floating_point_arithmetic

tools/similarity.c

@@ -25,7 +25,7 @@ int phase_mask[MAX_SIZE+MAX_SIZE];
 unsigned short microsoft_basic_chunks[NUM_CHUNKS * 2] = {
     0xB391, 0xB39D,
     0xB3A2, 0xB3A5,
-    0xB849, 0xB84F,
+    0xB849, 0xB853,
     0xB8D2, 0xB8D5,
     0xB947, 0xB97D,
     0xB983, 0xB9BB,