Update inv_FAC1

src/basic/math/b947.inv_FAC1.s

@@ -0,0 +1,44 @@
+;; #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 - neg (2s complement) FAC1
+;
+; This is verified to be identical to the original Microsoft implementation where it was named NEGFAC.
+;
+; The alternative entry point neg_FAC1_mantissa (NEGFCH) will negate only the mantissa
+;
+; See also:
+; - https://www.c64-wiki.com/wiki/BASIC-ROM
+; - https://sta.c64.org/cbm64basconv.html
+;
+
+neg_FAC1:
+	lda FAC1_sign
+	eor #$FF
+	sta FAC1_sign
+
+neg_FAC1_mantissa:
+
+    lda FAC1_mantissa+0
+    eor #$FF
+    sta FAC1_mantissa+0
+    lda FAC1_mantissa+1
+    eor #$FF
+    sta FAC1_mantissa+1
+    lda FAC1_mantissa+2
+    eor #$FF
+    sta FAC1_mantissa+2
+    lda FAC1_mantissa+3
+    eor #$FF
+    sta FAC1_mantissa+3
+    lda FACOV
+    eor #$FF
+    sta FACOV
+    bne inc_FAC1_ret
+    
+    ; Fallthrough to inc_FAC1

src/basic/math/b947.inv_FAC1_mantissa.s

@@ -1,36 +0,0 @@
-;; #LAYOUT# STD *       #TAKE
-;; #LAYOUT# X16 BASIC_0 #TAKE-OFFSET 2000
-;; #LAYOUT# *   BASIC_0 #TAKE
-;; #LAYOUT# *   *       #IGNORE
-
-;
-; Math package - invert FAC1 mantissa
-;
-; See also:
-; - [CM64] Computes Mapping the Commodore 64 - page 113
-; - https://www.c64-wiki.com/wiki/BASIC-ROM
-; - https://sta.c64.org/cbm64basconv.html
-;
-
-; 2-complement the FAC1 mantissa
-; The 4 byte mantissa is treated as an integer in big endian form
-
-
-inv_FAC1_mantissa:
-
-    ldx #3
-@1: lda FAC1_mantissa,X
-    eor #$FF
-    sta FAC1_mantissa,X
-    dex
-    bpl @1
-
-    inc FAC1_mantissa+3
-    bne @2
-    inc FAC1_mantissa+2
-    bne @2
-    inc FAC1_mantissa+1
-    bne @2
-    inc FAC1_mantissa
-    
-@2: rts