multiplication cleanup

STATUS.md

@@ -199,7 +199,7 @@ Floating point mathematical routines - not official, but well known and broadly
 | `$B947`   | `inv_FAC1_mantissa`    | NOT DONE |                                                    |
 | `$B9EA`   | `log_FAC1`             | NOT DONE |                                                    |
 | `$BA28`   | `mul_MEM_FAC1`         | DONE     |                                                    |
-| `$BA2B`   | `mul_FAC2_FAC1`        | PARTIAL  | sometime imprecise - like PI*PI                    |
+| `$BA2B`   | `mul_FAC2_FAC1`        | DONE     |                                                    |
 | `$BA8C`   | `mov_MEM_FAC2`         | DONE     |                                                    |
 | `$BA90`   | `get_FAC2_via_INDEX`   | NOT DONE |                                                    |
 | `$BAE2`   | `mul10_FAC1`           | DONE     |                                                    |

c64/basic/math/mul_FAC2_FAC1.s

@@ -17,8 +17,6 @@
 // - https://codebase64.org/doku.php?id=base:kernal_floating_point_mathematics
 //
 
-// XXX the code here is very imprecise, find out why
-
 mul_FAC2_FAC1_done:
 
 	rts
@@ -98,31 +96,31 @@ mul_FAC2_FAC1_sub_exp_bias:
 
 	lda FACOV
 	jsr mul_FAC2_FAC1_by_A
-	jsr mul_FAC2_FAC1_shift_RESHO
+	jsr mul_FAC2_FAC1_shift
 	bcc !+
 	inc RESHO+0
 !:
 	lda FAC1_mantissa+3
 	jsr mul_FAC2_FAC1_by_A
-	jsr mul_FAC2_FAC1_shift_RESHO
+	jsr mul_FAC2_FAC1_shift
 	bcc !+
 	inc RESHO+0
 !:
 	lda FAC1_mantissa+2
 	jsr mul_FAC2_FAC1_by_A
-	jsr mul_FAC2_FAC1_shift_RESHO
+	jsr mul_FAC2_FAC1_shift
 	bcc !+
 	inc RESHO+0
 !:
 	lda FAC1_mantissa+1
 	jsr mul_FAC2_FAC1_by_A
-	jsr mul_FAC2_FAC1_shift_RESHO
+	jsr mul_FAC2_FAC1_shift
 	bcc !+
 	inc RESHO+0
 !:
 	lda FAC1_mantissa+0
 	jsr mul_FAC2_FAC1_by_A
-	jsr mul_FAC2_FAC1_shift_RESHO
+	jsr mul_FAC2_FAC1_shift
 	bcc !+
 	inc RESHO+0
 !:
@@ -214,23 +212,3 @@ mul_FAC2_FAC1_by_A:
 mul_FAC2_FAC1_by_A_done:
 
 	rts
-
-
-
-
-mul_FAC2_FAC1_shift_RESHO: // XXX we should probably move this subroutine to a separate file
-
-	// Shift RESHO by one byte
-
-	lda RESHO+3
-	sta RESHO+4
-	lda RESHO+2
-	sta RESHO+3
-	lda RESHO+1
-	sta RESHO+2
-	lda RESHO+0
-	sta RESHO+1
-	lda #$00
-	sta RESHO+0
-
-	rts

c64/basic/math/mul_FAC2_FAC1_shift.s

@@ -0,0 +1,22 @@
+// #LAYOUT# STD *       #TAKE
+// #LAYOUT# *   BASIC_0 #TAKE
+// #LAYOUT# *   *       #IGNORE
+
+//
+// Shift RESHO by one byte - for multiplication
+//
+
+mul_FAC2_FAC1_shift:
+
+	lda RESHO+3
+	sta RESHO+4
+	lda RESHO+2
+	sta RESHO+3
+	lda RESHO+1
+	sta RESHO+2
+	lda RESHO+0
+	sta RESHO+1
+	lda #$00
+	sta RESHO+0
+
+	rts