Update convert_i16_to_FAC1

STATUS.md

@@ -237,7 +237,7 @@ Floating point mathematical routines - not official, but well known and broadly
 | `$BC2B`   | `sgn_FAC1_A`           | DONE     | From the Microsoft BASIC, original name: SIGN      |
 | `$BC39`   | `sgn_FAC1`             | DONE     | From the Microsoft BASIC, original name: SGN       |
 | `$BC3C`   | `convert_A_to_FAC1`    | DONE     | From the Microsoft BASIC, original name: FLOAT     |
-| `$BC44`   | `convert_i16_to_FAC1`  | DONE     |                                                    |
+| `$BC44`   | `convert_i16_to_FAC1`  | DONE     | From the Microsoft BASIC, original name: FLOATS    |
 | `$BC58`   | `abs_FAC1`             | DONE     | From the Microsoft BASIC, original name: ABS       |
 | `$BC5B`   | `FCOMP`                | DONE     |                                                    |
 | `$BC9B`   | `QINT`                 | DONE     | From the Microsoft BASIC, original name: QINT      |

src/basic/math/bc44.convert_i16_to_FAC1.s

@@ -3,27 +3,34 @@
 ;; #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 - Convert signed 16-bit integer to floating point
 ;
+; This is verified to be identical to the original Microsoft implementation where it was named FLOATS.
+;
 ; - https://codebase64.org/doku.php?id=base:kernal_floating_point_mathematics
 ; - https://www.c64-wiki.com/wiki/GIVAYF (which calls this function)
 ;
 ; Convert the signed 16-bit integer in FAC1 mantissa ($62:$63)
-; into a floating point number in FAC1
-
-; NOTE:
-; According to https://c64os.com/post/floatingpointmath at $BC49
-; Assume FAC1_mantissa+0 and +1. X=exponent and C=0 if negative and C=1 if positive
+; into a floating point number in FAC1. Assume X=exponent
+;
+; Alternative entry points:
+; FLOATC: Assume FAC1_mantissa+0 and +1 loaded. Assume CF=0 if negative and C=1 if positive
+; FLOATB: as for FLOATC and do not clear FAC1_mantissa+2 and +3 and set sign and FACOV to A
 
 convert_i16_to_FAC1:
-    ldx #$90
-    jsr carry
 
-    jmp convert_i16_expsign_to_FAC1   ; This should be at $BC49 (see note above)
-
-
-carry:
-    lda FAC1_mantissa
-    cmp #$80                    ; Copy sign into carry
-    rts
+    lda FAC1_mantissa+0
+    eor #$FF
+    rol                             ; CF = Complement of sign
+FLOATC:
+    lda #0
+    sta FAC1_mantissa+3
+    sta FAC1_mantissa+2
+FLOATB:
+    stx FAC1_exponent
+    sta FACOV
+    sta FAC1_sign
+    jmp abs_and_normal_FAC1

src/basic/math/convert_i16_expsign_to_FAC1.s

@@ -1,24 +0,0 @@
-;; #LAYOUT# STD *       #TAKE
-;; #LAYOUT# *   BASIC_0 #TAKE
-;; #LAYOUT# *   *       #IGNORE
-
-;
-; Math package - convert i16 with exponent in X and sign in C to FAC1
-
-convert_i16_expsign_to_FAC1:
-
-    lda #$00                    
-    sta FAC1_mantissa+2         ; Clear high bytes of mantissa
-    sta FAC1_mantissa+3
-    stx FAC1_exponent
-    sta FAC1_sign
-    bcc @1
-
-    ; Handle signed int
-    lda FAC1_mantissa            ; Clear sign bit of int 16
-    and #$7F
-    sta FAC1_mantissa
-    ldy #>CONST_NEG_32768       ; Subtract with 32768 to invert negative number
-    lda #<CONST_NEG_32768
-    jsr add_MEM_FAC1
-@1: jmp normal_FAC1

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 7
 // Pairs of start, end memory addresses of known exact similarity with the open source Microsoft BASIC
 unsigned short microsoft_basic_chunks[NUM_CHUNKS * 2] = {
     0xB849, 0xB84F,
@@ -28,8 +28,7 @@ unsigned short microsoft_basic_chunks[NUM_CHUNKS * 2] = {
     0xB947, 0xB97D,
     0xB983, 0xB9BB,
     0xBBA2, 0xBC1A,
-    0xBC2B, 0xBC43,
-    0xBC58, 0xBC5A,
+    0xBC2B, 0xBC5A,
     0xBC9B, 0xBCF2,
 };