Add get_FAC1_via_INDEX

Also change to only use bit 7 as sign in FAC1 and FAC2 (as the original BASIC does) to simplify
implementations.

src/basic/math_mov/ba90.get_FAC2_via_INDEX.s

@@ -33,20 +33,10 @@ get_FAC2_via_INDEX:
 
 	dey
 	lda (INDEX), y
+	sta FAC2_sign
 	ora #$80                           ; clear the sign bit
 	sta FAC2_mantissa+0
 
-	; Copy the sign
-
-	lda (INDEX), y
-	bpl @1                             ; assumption: non-negative numbers are more frequent
-	lda #$FF
-	+skip_2_bytes_trash_nvz
-@1:
-	lda #$00
-
-	sta FAC2_sign
-
 	; Copy the exponent
 
 	dey

src/basic/math_mov/bba2.mov_MEM_FAC1.jmp.s

@@ -1,8 +0,0 @@
-;; #LAYOUT# STD *       #TAKE
-;; #LAYOUT# X16 BASIC_0 #TAKE-OFFSET 2000
-;; #LAYOUT# *   BASIC_0 #TAKE
-;; #LAYOUT# *   *       #IGNORE
-
-; Just a compatibility jump - our routine is longer than original one
-
-	jmp mov_MEM_FAC1

src/basic/math_mov/bba2.mov_MEM_FAC1.s

@@ -0,0 +1,30 @@
+;; #LAYOUT# STD *       #TAKE
+;; #LAYOUT# X16 BASIC_0 #TAKE-OFFSET 2000
+;; #LAYOUT# *   BASIC_0 #TAKE
+;; #LAYOUT# *   *       #IGNORE
+
+
+; Math package - fetch FAC1 from RAM location
+;
+; Input:
+; - .A - address low byte
+; - .Y - address high byte
+;
+; Output:
+; - .A - FAC1 exponent, affects status flags
+; - .Y - always 0
+;
+; Preserves:
+; - .X - (experimentation with original ROM)
+;
+; See also:
+; - https://www.c64-wiki.com/wiki/Floating_point_arithmetic
+; - https://codebase64.org/doku.php?id=base:kernal_floating_point_mathematics
+
+
+
+mov_MEM_FAC1:
+	sty INDEX+1
+	sta INDEX+0
+
+    ; FALLTHROUGH to get_FAC1_via_INDEX

src/basic/math_mov/bba6.get_FAC1_via_INDEX.s

@@ -0,0 +1,45 @@
+;; #LAYOUT# STD *       #TAKE
+;; #LAYOUT# X16 BASIC_0 #TAKE-OFFSET 2000
+;; #LAYOUT# *   BASIC_0 #TAKE
+;; #LAYOUT# *   *       #IGNORE
+
+; Math package - Mov MEM to FAC1 with address in INDEX zero page register
+;
+; See also:
+; - https://sourceforge.net/p/acme-crossass/code-0/38/tree/trunk/ACME_Lib/cbm/c64/float.a?force=True
+;
+
+get_FAC1_via_INDEX:
+
+	; Copy the mantissa
+
+	ldy #$04
+	lda (INDEX), y
+	sta FAC1_mantissa+3
+
+	dey
+	lda (INDEX), y
+	sta FAC1_mantissa+2
+
+	dey
+	lda (INDEX), y
+	sta FAC1_mantissa+1
+
+	dey
+	lda (INDEX), y
+	sta FAC1_sign
+	ora #$80                           ; clear the sign bit
+	sta FAC1_mantissa+0
+
+	; Copy the exponent
+
+	dey
+	lda (INDEX), y
+	sta FAC1_exponent
+
+	; Set low order mantissa to 0 - this should give the
+	; most precision while operating on integers
+
+	sty FACOV
+
+	rts

src/basic/math_mov/bba6.interop

@@ -0,0 +1,4 @@
+This is an important floating point math routine, documented in many places.
+
+It's a part oof the ACME assembler SDK, see:
+- https://sourceforge.net/p/acme-crossass/code-0/38/tree/trunk/ACME_Lib/cbm/c64/float.a?force=True

src/basic/math_mov/mov_MEM_FAC1.s

@@ -1,79 +0,0 @@
-;; #LAYOUT# STD *       #TAKE
-;; #LAYOUT# *   BASIC_0 #TAKE
-;; #LAYOUT# *   *       #IGNORE
-
-; Math package - fetch FAC1 from RAM location
-;
-; Input:
-; - .A - address low byte
-; - .Y - address high byte
-;
-; Output:
-; - .A - FAC1 exponent, affects status flags
-; - .Y - always 0
-;
-; Preserves:
-; - .X - (experimentation with original ROM)
-;
-; See also:
-; - https://www.c64-wiki.com/wiki/Floating_point_arithmetic
-; - https://codebase64.org/doku.php?id=base:kernal_floating_point_mathematics
-
-; XXX test this
-
-mov_MEM_FAC1:
-
-	; Original routines use $22/$23 location for a vector too, see here:
-	; - https://codebase64.org/doku.php?id=base:kernal_floating_point_mathematics
-
-	sty INDEX+1
-	sta INDEX+0
-
-	; Now copy the data from RAM to FAC2, for the format description see:
-	; - https://www.c64-wiki.com/wiki/Floating_point_arithmetic#Representation_in_the_C-64
-
-	; Copy the mantissa
-
-	ldy #$04
-	lda (INDEX), y
-	sta FAC1_mantissa+3
-
-	dey
-	lda (INDEX), y
-	sta FAC1_mantissa+2
-
-	dey
-	lda (INDEX), y
-	sta FAC1_mantissa+1
-
-	dey
-	lda (INDEX), y
-	ora #$80                           ; clear the sign bit
-	sta FAC1_mantissa+0
-
-	; Copy the sign
-
-	lda (INDEX), y
-	bpl @1                             ; assumption: non-negative numbers are more frequent
-	lda #$FF
-	+skip_2_bytes_trash_nvz
-@1:
-	lda #$00
-
-	sta FAC1_sign
-
-	; Copy the exponent
-
-	dey
-	lda (INDEX), y
-	sta FAC1_exponent
-
-	; Set low order mantissa to 0 - this should give the
-	; most precision while operating on integers
-
-	sty FACOV
-
-	; Return the FAC1 exponent
-
-	lda FAC1_exponent
-	rts