Add zero_FAC1

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