Add NORM2

src/basic/math/b91d.NORM2.s

@@ -0,0 +1,35 @@
+;; #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 - continuation of normalize FAC1 function
+;
+; This is verified to be identical to the original Microsoft implementation where it was named NORM2.
+;
+; 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
+;
+
+NORM2:
+    adc #1              ; Decrement shift count
+    asl FACOV           ; Shift all left one bit
+    rol FAC1_mantissa+3
+    rol FAC1_mantissa+2
+    rol FAC1_mantissa+1
+    rol FAC1_mantissa+0
+NORM1:
+    bpl NORM2           ; If MSB=0 shift again
+    sec
+    sbc FAC1_exponent
+    bcs zero_FAC1
+    eor #$FF
+    adc #1              ; Complement
+    sta FAC1_exponent
+    
+    ; Fallthrough to shift_carry_into_FAC1