Add compute_ST

src/basic/math/af9a.compute_ST.s

@@ -0,0 +1,16 @@
+;; #LAYOUT# STD *       #TAKE
+;; #LAYOUT# X16 BASIC_0 #TAKE-OFFSET 2000
+;; #LAYOUT# *   BASIC_0 #TAKE
+;; #LAYOUT# *   *       #IGNORE
+
+;
+; Math package - compute ST value
+;
+; See also:
+; - https://www.c64-wiki.com/wiki/BASIC-ROM
+;
+
+compute_ST:
+
+	lda IOSTATUS
+	jmp convert_A_to_FAC1

src/basic/math/af9a.interop

@@ -0,0 +1,3 @@
+This is an important floating point math routine, documented in many places.
+
+XXX - try to find real-life example