Update GIVAYF

src/basic/math/b391.GIVAYF.s

@@ -3,7 +3,9 @@
 ;; #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 - 16-bit signed integer to FAC1
 ;
 ; Output:
@@ -13,6 +15,8 @@
 ; Sets the data type flag at $0D to "numeric", stores the number in the FAC1 mantissa
 ; then calls convert_i16_to_FAC1
 ;
+; This is verified to be identical to the original Microsoft implementation where it was named GIVAYF.
+;
 ; See also:
 ; - [CM64] Computes Mapping the Commodore 64 - page 107
 ; - https://www.c64-wiki.com/wiki/GIVAYF
@@ -20,8 +24,9 @@
 
 
 GIVAYF:
-    ldx #$00
-    stx $0D
-    sty FAC1_mantissa
-    sta FAC1_mantissa+1
+    ldx #0
+    stx VALTYP
+    sta FAC1_mantissa+0
+	sty FAC1_mantissa+1
+    ldx #$90
     jmp convert_i16_to_FAC1