Update mov_FAC2_FAC1 to match the original implementation

STATUS.md

@@ -227,7 +227,7 @@ Floating point mathematical routines - not official, but well known and broadly
 | `$BBCA`   | `mov_r_FAC1_TMP1`      | PARTIAL  | not fully tested yet                               |
 | `$BBD0`   | `mov_r_FAC1_VAR`       | PARTIAL  | not fully tested yet                               |
 | `$BBD4`   | `mov_r_FAC1_MEM`       | PARTIAL  | not fully tested yet                               |
-| `$BBFC`   | `mov_FAC2_FAC1`        | DONE     |                                                    |
+| `$BBFC`   | `mov_FAC2_FAC1`        | DONE     | From the Microsoft BASIC, original name: MOVFA     |
 | `$BC0C`   | `mov_r_FAC1_FAC2`      | DONE     | From the Microsoft BASIC, original name: MOVAF     |
 | `$BC0F`   | `mov_FAC1_FAC2`        | DONE     | From the Microsoft BASIC, original name: MOVEF     |
 | `$BC1B`   | `round_FAC1`           | PARTIAL  | not fully tested yet                               |

src/basic/math_mov/bbfc.mov_FAC2_FAC1.s

@@ -3,6 +3,45 @@
 ;; #LAYOUT# *   BASIC_0 #TAKE
 ;; #LAYOUT# *   *       #IGNORE
 
-; Just a compatibility jump - our routine is longer than original one
+; This file is under the MIT license, it contains code released by Microsoft Corporation.
+; See LICENSE for more information.
 
-	jmp mov_FAC2_FAC1
+; Math package - Copy FAC2 to FAC1
+;
+; This is verified to be identical to the original Microsoft implementation where it was named MOVFA.
+;
+; It has an alternative entry point at mov_FAC2_FAC1_sign (original: MOVFA1) that instead of copying the sign uses A for the copied sign.
+;
+; Output (found by experimentation):
+; - .A - FAC1 exponent
+; - .X - always 0
+;
+; Preserves:
+; - .Y
+;
+; See also:
+; - [CM64] Computes Mapping the Commodore 64 - page 115
+; - https://www.c64-wiki.com/wiki/Floating_point_arithmetic
+; - https://codebase64.org/doku.php?id=base:kernal_floating_point_mathematics
+;
+
+
+mov_FAC2_FAC1:
+    ; Copy the sign
+
+    lda FAC2_sign
+
+mov_FAC2_FAC1_sign:
+    sta FAC2_sign
+
+    ; Copy the mantissa and the exponent
+
+    ldx #5
+
+@1
+    lda FAC2_exponent - 1,X
+    sta FAC1_exponent - 1,X
+    dex
+    bne @1
+    stx FACOV           ; Always 0
+    rts

src/basic/math_mov/mov_FAC2_FAC1.s

@@ -1,49 +0,0 @@
-;; #LAYOUT# STD *       #TAKE
-;; #LAYOUT# *   BASIC_0 #TAKE
-;; #LAYOUT# *   *       #IGNORE
-
-;
-; Math package - copy FAC2 to FAC1
-;
-; Output (found by experimentation):
-; - .A - FAC1 exponent
-; - .X - always 0
-;
-; Preserves:
-; - .Y
-;
-; See also:
-; - [CM64] Computes Mapping the Commodore 64 - page 115
-; - https://www.c64-wiki.com/wiki/Floating_point_arithmetic
-; - https://codebase64.org/doku.php?id=base:kernal_floating_point_mathematics
-;
-
-mov_FAC2_FAC1:
-
-	; Copy the mantissa
-
-	lda FAC2_mantissa+3
-	sta FAC1_mantissa+3
-	lda FAC2_mantissa+2
-	sta FAC1_mantissa+2
-	lda FAC2_mantissa+1
-	sta FAC1_mantissa+1
-	lda FAC2_mantissa+0
-	sta FAC1_mantissa+0
-
-	; Copy the sign
-
-	lda FAC2_sign
-	sta FAC1_sign
-
-	; Copy the exponent
-
-	lda FAC2_exponent
-	sta FAC1_exponent
-
-	; Clear FACOV
-
-	ldx #$00
-	stx FACOV
-
-	rts

tools/similarity.c

@@ -22,7 +22,7 @@ int phase_mask[MAX_SIZE+MAX_SIZE];
 
 #define NUM_CHUNKS 1
 // Pairs of start, end memory addresses of known exact similarity with the open source Microsoft BASIC
-unsigned short microsoft_basic_chunks[NUM_CHUNKS * 2] = {0xBC0C, 0xBC1A};
+unsigned short microsoft_basic_chunks[NUM_CHUNKS * 2] = {0xBBFC, 0xBC1A};
 
 
 int main(int argc,char **argv)