various multiplication fixes

STATUS.md

@@ -198,11 +198,11 @@ Floating point mathematical routines - not official, but well known and broadly
 | `$B8FE`   | `normal_FAC1`          | DONE     |                                                    |
 | `$B947`   | `inv_FAC1_mantissa`    | NOT DONE |                                                    |
 | `$B9EA`   | `log_FAC1`             | NOT DONE |                                                    |
-| `$BA28`   | `mul_MEM_FAC1`         | PARTIAL  | needs `mul_FAC2_FAC1`                              |
+| `$BA28`   | `mul_MEM_FAC1`         | DONE     |                                                    |
-| `$BA2B`   | `mul_FAC2_FAC1`        | PARTIAL  | not testeed yet                                    |
+| `$BA2B`   | `mul_FAC2_FAC1`        | PARTIAL  | very imprecise; not yet clear, why                 |
 | `$BA8C`   | `mov_MEM_FAC2`         | DONE     |                                                    |
 | `$BA90`   | `get_FAC2_via_INDEX`   | NOT DONE |                                                    |
-| `$BAE2`   | `mul10_FAC1`           | PARTIAL  | not tested yet                                     |
+| `$BAE2`   | `mul10_FAC1`           | DONE     |                                                    |
 | `$BAFE`   | `div10_FAC1_p`         | PARTIAL  | needs `div_FAC2_FAC1`                              |
 | `$BB0F`   | `div_MEM_FAC1`         | PARTIAL  | needs `div_FAC2_FAC1`                              |
 | `$BB12`   | `div_FAC2_FAC1`        | NOT DONE | some work already started                          |

c64/basic/math/bae2.mul10_FAC1.s

@@ -12,8 +12,6 @@
 // - https://codebase64.org/doku.php?id=base:kernal_floating_point_mathematics
 //
 
-// XXX test this
-
 mul10_FAC1:
 
 	// Handle special case of FAC1 equal 0

c64/basic/math/mul10_FAC1_mul2.s

@@ -11,6 +11,6 @@ mul10_FAC1_mul2:
 	// Increment the exponent
 
 	inc FAC1_exponent
-	bcs_16 set_FAC1_max
+	beq_16 set_FAC1_max
 
 	rts

c64/basic/math/mul_FAC2_FAC1.s

@@ -17,7 +17,7 @@
 // - https://codebase64.org/doku.php?id=base:kernal_floating_point_mathematics
 //
 
-// XXX test this code
+// XXX the code here is very imprecise, find out why
 
 mul_FAC2_FAC1_done:
 
@@ -139,7 +139,13 @@ mul_FAC2_FAC1_sub_exp_bias:
 	lda RESHO+0
 	sta FAC1_mantissa+0
 
-	// XXX correction is probably needed
+	// Correct the exponent
+
+	lda FAC1_exponent
+	clc
+	adc #$08
+	bcs_16 set_FAC1_max                // branch if overflow
+	sta FAC1_exponent
 
 	jmp normal_FAC1
 
@@ -153,7 +159,7 @@ mul_by_A: // XXX we should probably move this subroutine to a separate file
 	// Multiply FAC2_mantissa+3
 
 	lda FAC2_mantissa+3
-	jsr mul_8x8
+	jsr mul_FAC2_FAC1_8x8
 
 	adc RESHO+4
 	sta RESHO+4
@@ -170,7 +176,7 @@ mul_by_A: // XXX we should probably move this subroutine to a separate file
 	// Multiply FAC2_mantissa+2
 
 	lda FAC2_mantissa+2
-	jsr mul_8x8
+	jsr mul_FAC2_FAC1_8x8
 
 	adc RESHO+3
 	sta RESHO+3
@@ -185,7 +191,7 @@ mul_by_A: // XXX we should probably move this subroutine to a separate file
 	// Multiply FAC2_mantissa+1
 
 	lda FAC2_mantissa+1
-	jsr mul_8x8
+	jsr mul_FAC2_FAC1_8x8
 
 	adc RESHO+2
 	sta RESHO+2
@@ -198,7 +204,7 @@ mul_by_A: // XXX we should probably move this subroutine to a separate file
 	// Multiply FAC2_mantissa+0
 
 	lda FAC2_mantissa+0
-	jsr mul_8x8
+	jsr mul_FAC2_FAC1_8x8
 	adc RESHO+1
 	sta RESHO+1
 	txa
@@ -225,66 +231,3 @@ mul_shift_RESHO: // XXX we should probably move this subroutine to a separate fi
 	sta RESHO+0
 
 	rts
-
-
-mul_8x8: // XXX we should probably move this subroutine to a separate file
-
-	sta INDEX+2
-
-	// Routine based on code by djmips, taken from:
-	// - https://codebase64.org/doku.php?id=base:8bit_multiplication_16bit_product_fast_no_tables
-	//
-	// input: INDEX+2, INDEX+3
-	// output: .X (high byte), .A and INDEX+2 (low byte), carry always clear
-
-	lda #$00
-
-	dec INDEX+3	// decrement because we will be adding with carry set for speed (an extra one)
-	ror INDEX+2
-	bcc !+
-	adc INDEX+3
-!:
-	ror
-	ror INDEX+2
-	bcc !+
-	adc INDEX+3
-!:
-	ror
-	ror INDEX+2
-	bcc !+
-	adc INDEX+3
-!:
-	ror
-	ror INDEX+2
-	bcc !+
-	adc INDEX+3
-!:
-	ror
-	ror INDEX+2
-	bcc !+
-	adc INDEX+3
-!:
-	ror
-	ror INDEX+2
-	bcc !+
-	adc INDEX+3
-!:
-	ror
-	ror INDEX+2
-	bcc !+
-	adc INDEX+3
-!:
-	ror
-	ror INDEX+2
-	bcc !+
-	adc INDEX+3
-!:
-	ror
-	ror INDEX+2
-	inc INDEX+3
-
-	tax
-	lda INDEX+2
-	clc
-
-	rts

c64/basic/math/mul_FAC2_FAC1_8x8.s

@@ -0,0 +1,67 @@
+// #LAYOUT# STD *       #TAKE
+// #LAYOUT# *   BASIC_0 #TAKE
+// #LAYOUT# *   *       #IGNORE
+
+//
+// Helper routine, based on code by djmips from:
+// - https://codebase64.org/doku.php?id=base:8bit_multiplication_16bit_product_fast_no_tables
+//
+// input: .A, INDEX+3
+// output: .X (high byte), .A and INDEX+2 (low byte), carry always clear
+//
+
+mul_FAC2_FAC1_8x8:
+
+	sta INDEX+2
+
+	lda #$00
+
+	dec INDEX+3	// decrement because we will be adding with carry set for speed (an extra one)
+	ror INDEX+2
+	bcc !+
+	adc INDEX+3
+!:
+	ror
+	ror INDEX+2
+	bcc !+
+	adc INDEX+3
+!:
+	ror
+	ror INDEX+2
+	bcc !+
+	adc INDEX+3
+!:
+	ror
+	ror INDEX+2
+	bcc !+
+	adc INDEX+3
+!:
+	ror
+	ror INDEX+2
+	bcc !+
+	adc INDEX+3
+!:
+	ror
+	ror INDEX+2
+	bcc !+
+	adc INDEX+3
+!:
+	ror
+	ror INDEX+2
+	bcc !+
+	adc INDEX+3
+!:
+	ror
+	ror INDEX+2
+	bcc !+
+	adc INDEX+3
+!:
+	ror
+	ror INDEX+2
+	inc INDEX+3
+
+	tax
+	lda INDEX+2
+	clc
+
+	rts