Add zero_FAC1

STATUS.md

@@ -211,6 +211,7 @@ Floating point mathematical routines - not official, but well known and broadly
 | `$B867`   | `add_MEM_FAC1`         | DONE     | From the Microsoft BASIC, original name: FADD      |
 | `$B86A`   | `add_FAC2_FAC1`        | DONE     |                                                    |
 | `$B8D2`   | `abs_and_normal_FAC`   | DONE     | From the Microsoft BASIC, original name: FADFLT    |
+| `$B8F7`   | `zero_FAC1`            | DONE     | From the Microsoft BASIC, original name: ZEROFC    |
 | `$B8FE`   | `normal_FAC1`          | DONE     |                                                    |
 | `$B947`   | `inv_FAC1_mantissa`    | DONE     | From the Microsoft BASIC, original name: NEGFAC    |
 | `$B96F`   | `inc_FAC1`             | DONE     | From the Microsoft BASIC, original name: INCFAC    |

src/basic/math/b8f7.zero_FAC1.s

@@ -0,0 +1,28 @@
+;; #LAYOUT# STD *       #TAKE
+;; #LAYOUT# X16 BASIC_0 #TAKE-OFFSET 2000
+;; #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 - zero FAC1 exponent and sign
+;
+; This is verified to be identical to the original Microsoft implementation where it was named ZEROFC.
+;
+; Alternative entry points ZEROF1 if A alread is 0 and ZEROML to store A to sign only.
+;
+; See also:
+; - [CM64] Computes Mapping the Commodore 64 - page 113
+; - https://www.c64-wiki.com/wiki/Floating_point_arithmetic
+; - https://codebase64.org/doku.php?id=base:kernal_floating_point_mathematics
+;
+
+
+zero_FAC1:
+    lda #0
+ZEROF1:
+    sta FAC1_exponent
+ZEROML:
+    sta FAC1_sign
+    rts

tools/similarity.c

@@ -20,13 +20,14 @@ int matches[MAX_SIZE];
 
 int phase_mask[MAX_SIZE+MAX_SIZE];
 
-#define NUM_CHUNKS 9
+#define NUM_CHUNKS 10
 // 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, 0xB869,
     0xB8D2, 0xB8D5,
+    0xB8F7, 0xB8FD,
     0xB947, 0xB97D,
     0xB983, 0xB9BB,
     0xBA8C, 0xBAB6,