Update mov_MEM_FAC2 and get_FAC2_via_INDEX

STATUS.md

@@ -218,8 +218,8 @@ Floating point mathematical routines - not official, but well known and broadly
 | `$B9EA`   | `log_FAC1`             | PARTIAL  | not fully tested yet                               |
 | `$BA28`   | `mul_MEM_FAC1`         | DONE     |                                                    |
 | `$BA2B`   | `mul_FAC2_FAC1`        | DONE     |                                                    |
-| `$BA8C`   | `mov_MEM_FAC2`         | DONE     |                                                    |
-| `$BA90`   | `get_FAC2_via_INDEX`   | DONE     |                                                    |
+| `$BA8C`   | `mov_MEM_FAC2`         | DONE     | From the Microsoft BASIC, original name: CONUPK    |
+| `$BA90`   | `get_FAC2_via_INDEX`   | DONE     | From the Microsoft BASIC, no label                 |
 | `$BAE2`   | `mul10_FAC1`           | DONE     |                                                    |
 | `$BAFE`   | `div10_FAC1_p`         | DONE     |                                                    |
 | `$BB0F`   | `div_MEM_FAC1`         | DONE     |                                                    |

src/basic/math_mov/ba8c.mov_MEM_FAC2.s

@@ -2,7 +2,10 @@
 ;; #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 - fetch FAC2 from memory location
 ;
 ; Input:
@@ -16,6 +19,8 @@
 ; Preserves:
 ; - .X - (experimentation with original ROM)
 ;
+; This is verified to be identical to the original Microsoft implementation where it was named CONUPK.
+;
 ; See also:
 ; - [CM64] Computes Mapping the Commodore 64 - page 114
 ; - https://www.c64-wiki.com/wiki/Floating_point_arithmetic
@@ -24,7 +29,7 @@
 
 
 mov_MEM_FAC2:
-	sty INDEX+1
-	sta INDEX+0
+    sta INDEX+0
+    sty INDEX+1
 
     ; FALLTHROUGH to get_FAC2_via_INDEX

src/basic/math_mov/ba90.get_FAC2_via_INDEX.s

@@ -3,9 +3,13 @@
 ;; #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 - Mov MEM to FAC2 with address in INDEX zero page register
 ;
+; This is verified to be identical to the original Microsoft implementation where it was named CONUPK (partial).
+;
 ; See also:
 ; - https://sourceforge.net/p/acme-crossass/code-0/38/tree/trunk/ACME_Lib/cbm/c64/float.a?force=True
 ;
@@ -14,36 +18,25 @@
 
 get_FAC2_via_INDEX:
 
-	; 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 FAC2_mantissa+3
-
-	dey
-	lda (INDEX), y
-	sta FAC2_mantissa+2
-
-	dey
-	lda (INDEX), y
-	sta FAC2_mantissa+1
-
-	dey
-	lda (INDEX), y
-	sta FAC2_sign
-	ora #$80                           ; clear the sign bit
-	sta FAC2_mantissa+0
-
-	; Copy the exponent
-
-	dey
-	lda (INDEX), y
-	sta FAC2_exponent
-
-	; Return the FAC1 exponent
-
-	lda FAC1_exponent
-	rts
+    ldy #4
+    lda (INDEX),Y
+    sta FAC2_mantissa+3
+    dey
+    lda (INDEX),Y
+    sta FAC2_mantissa+2
+    dey
+    lda (INDEX),Y
+    sta FAC2_mantissa+1
+    dey
+    lda (INDEX),Y
+    sta FAC2_sign
+    eor FAC1_sign           ; Set sign for multiplication/division
+    sta ARISGN
+    lda FAC2_sign
+    ora #$80                ; Set mantissa high bit
+    sta FAC2_mantissa+0
+    dey
+    lda (INDEX),Y
+    sta FAC2_exponent
+    lda FAC1_exponent       ; Set flags from FAC1_exponent
+    rts

tools/similarity.c

@@ -20,7 +20,7 @@ int matches[MAX_SIZE];
 
 int phase_mask[MAX_SIZE+MAX_SIZE];
 
-#define NUM_CHUNKS 8
+#define NUM_CHUNKS 9
 // Pairs of start, end memory addresses of known exact similarity with the open source Microsoft BASIC
 unsigned short microsoft_basic_chunks[NUM_CHUNKS * 2] = {
     0xB391, 0xB39D,
@@ -29,6 +29,7 @@ unsigned short microsoft_basic_chunks[NUM_CHUNKS * 2] = {
     0xB8D2, 0xB8D5,
     0xB947, 0xB97D,
     0xB983, 0xB9BB,
+    0xBA8C, 0xBAB6,
     0xBBA2, 0xBC1A,
     0xBC2B, 0xBCF2,
 };