fixes for floating point subtraction

c64/basic/math/add_FAC2_FAC1_sub.s

@@ -0,0 +1,107 @@
+// #LAYOUT# STD *       #TAKE
+// #LAYOUT# X16 BASIC_0 #TAKE-OFFSET 2000
+// #LAYOUT# *   BASIC_0 #TAKE
+// #LAYOUT# *   *       #IGNORE
+
+//
+// Math package - add FAC2 to FAC1, subtraction part
+//
+
+// XXX test this
+
+add_FAC2_FAC1_sub:
+
+	// First verify that |FAC1| > |FAC2|, branch to proper variant if it is not
+	// Note, that exponents are laready equalized
+
+	lda FAC1_mantissa+0
+	cmp FAC2_mantissa+0
+	bcc add_FAC2_FAC1_sub_rev          // if FAC1 < FAC2, branch
+	bne !+                             // if FAC1 > FAC2, branch
+
+	lda FAC1_mantissa+1
+	cmp FAC2_mantissa+1
+	bcc add_FAC2_FAC1_sub_rev          // if FAC1 < FAC2, branch
+	bne !+                             // if FAC1 > FAC2, branch
+
+	lda FAC1_mantissa+2
+	cmp FAC2_mantissa+2
+	bcc add_FAC2_FAC1_sub_rev          // if FAC1 < FAC2, branch
+	bne !+                             // if FAC1 > FAC2, branch
+
+	lda FAC1_mantissa+3
+	cmp FAC2_mantissa+3
+	bcc add_FAC2_FAC1_sub_rev          // if FAC1 < FAC2, branch
+	bne !+                             // if FAC1 > FAC2, branch
+
+	// If we are here, than FAC1 is equal to FAC2 - so just set FAC1 to 0
+	
+	lda #$00
+	sta FAC1_exponent
+	rts
+!:
+	// Perform the subtration, FAC1 = FAC1 - FAC2
+
+	sec
+	lda FAC1_mantissa+3
+	sbc FAC2_mantissa+3
+	sta FAC1_mantissa+3
+
+	lda FAC1_mantissa+2
+	sbc FAC2_mantissa+2
+	sta FAC1_mantissa+2
+	
+	lda FAC1_mantissa+1
+	sbc FAC2_mantissa+1
+	sta FAC1_mantissa+1	
+
+	lda FAC1_mantissa+0
+	sbc FAC2_mantissa+0
+	sta FAC1_mantissa+0	
+	
+	bcs add_FAC2_FAC1_sub_normalize    // end if no need to adapt the exponent
+
+	dec FAC1_exponent
+	
+	jmp normal_FAC1
+
+add_FAC2_FAC1_sub_rev:
+
+	// Since |FAC1| < |FAC2|, toggle FAC1 sign before subtraction
+
+	jsr toggle_sign_FAC1_skipcheck
+
+	// Perform the subtration, FAC1 = FAC2 - FAC1
+	
+	sec
+	lda #$00
+	sbc FACOV
+	sta FACOV
+	
+	lda FAC2_mantissa+3
+	sbc FAC1_mantissa+3
+	sta FAC1_mantissa+3
+
+	lda FAC2_mantissa+2
+	sbc FAC1_mantissa+2
+	sta FAC1_mantissa+2
+	
+	lda FAC2_mantissa+1
+	sbc FAC1_mantissa+1
+	sta FAC1_mantissa+1	
+
+	lda FAC2_mantissa+0
+	sbc FAC1_mantissa+0
+	sta FAC1_mantissa+0
+	
+	bcs add_FAC2_FAC1_sub_normalize    // end if no need to adapt the exponent
+	
+	lda FAC2_exponent
+	sta FAC1_exponent
+	dec FAC1_exponent
+	
+	// FALLTROUGH
+
+add_FAC2_FAC1_sub_normalize:
+
+	jmp normal_FAC1

c64/basic/math/b86a.add_FAC2_FAC1.s

@@ -41,7 +41,7 @@ add_FAC2_FAC1:
 	lda FAC1_sign
 	eor FAC2_sign
 
-	bmi add_FAC2_FAC1_sub              // branch if signs are opposite
+	bmi_16 add_FAC2_FAC1_sub           // branch if signs are opposite
 
 	// Perform the addition
 	
@@ -66,8 +66,6 @@ add_FAC2_FAC1:
 
 	inc FAC1_exponent
 	bne add_FAC2_FAC1_normalize        // end if no overflow
-
-	// Overflow - XXX shouldnt we mark it somewhere in memory?
 	
 	lda #$FF
 	sta FAC1_exponent
@@ -82,33 +80,6 @@ add_FAC2_FAC1_done:
 
 	rts
 
-add_FAC2_FAC1_sub:
-
-	// Perform the subtration
-
-	sec
-	lda FAC1_mantissa+3
-	sbc FAC2_mantissa+3
-	sta FAC1_mantissa+3
-
-	lda FAC1_mantissa+2
-	sbc FAC2_mantissa+2
-	sta FAC1_mantissa+2
-	
-	lda FAC1_mantissa+1
-	sbc FAC2_mantissa+1
-	sta FAC1_mantissa+1	
-
-	lda FAC1_mantissa+0
-	sbc FAC2_mantissa+0
-	sta FAC1_mantissa+0	
-	
-	bcs add_FAC2_FAC1_normalize          // end if no need to adapt the exponent
-
-	dec FAC1_exponent
-	
-	// FALLTROUGH
-	
 add_FAC2_FAC1_normalize:
 	
 	jmp normal_FAC1

c64/basic/math/bfb4.toggle_sign_FAC1.s

@@ -16,6 +16,10 @@ toggle_sign_FAC1:
 	lda FAC1_exponent
 	beq !+                             // do not toggle the sign if value is 0
 
+	// FALLTROUGH
+
+toggle_sign_FAC1_skipcheck:            // entry for other routines
+
 	lda FAC1_sign
 	eor #$FF
 	sta FAC1_sign