From e16118a331b123baa65e6ad51d256c8bd86724f4 Mon Sep 17 00:00:00 2001
From: FeralChild64 <you@example.com>
Date: Sat, 21 Mar 2020 15:53:40 +0100
Subject: [PATCH] reversed botched attempt to increase FP division precission

---
 c64/basic/math/bb12.div_FAC2_FAC1.s |  5 +----
 c64/basic/math/div_FAC1_denorm.s    | 15 ++++++++-------
 c64/basic/math/div_mantissas.s      | 18 +++++-------------
 3 files changed, 14 insertions(+), 24 deletions(-)

diff --git a/c64/basic/math/bb12.div_FAC2_FAC1.s b/c64/basic/math/bb12.div_FAC2_FAC1.s
index 563422b1..583572dc 100644
--- a/c64/basic/math/bb12.div_FAC2_FAC1.s
+++ b/c64/basic/math/bb12.div_FAC2_FAC1.s
@@ -37,7 +37,7 @@ div_FAC2_FAC1:
 	beq_16 set_FAC1_zero
 
 	// Multiply signs
-	
+
 	lda FAC1_sign
 	eor FAC2_sign
 	sta FAC1_sign
@@ -85,9 +85,6 @@ div_FAC2_FAC1:
 	lda FAC2_mantissa+0
 	sta FAC1_mantissa+0
 
-	lda #$00
-	sta FACOV
-
 	// Normalize and quit
 	
 	jmp normal_FAC1
diff --git a/c64/basic/math/div_FAC1_denorm.s b/c64/basic/math/div_FAC1_denorm.s
index fb1150f9..228eb88f 100644
--- a/c64/basic/math/div_FAC1_denorm.s
+++ b/c64/basic/math/div_FAC1_denorm.s
@@ -3,17 +3,21 @@
 // #LAYOUT# *   *       #IGNORE
 
 //
-// Math package - denormalize FAC1 mantissa and adapt its exponent accordingly,
-// so that division is more precise
+// Math package - denormalize FAC1 mantissa and adapt its exponent accordingly
 //
 
 // XXX test this
 
 div_FAC1_denorm:
 
+	// Set FACOV to 0, no need for increased precision here
+
+	lda #$00
+	sta FACOV
+
 	// Start by moving whole bytes, if possible
 
-	lda FACOV
+	lda FAC1_mantissa+3
 	bne div_FAC1_denorm_by_bit         // branch if last byte of mantissa is non-zero
 
 	lda FAC1_exponent
@@ -27,8 +31,6 @@ div_FAC1_denorm:
 
 	// Move mantissa bytes
 
-	lda FAC1_mantissa+3
-	sta FACOV
 	lda FAC1_mantissa+2
 	sta FAC1_mantissa+3
 	lda FAC1_mantissa+1
@@ -42,7 +44,7 @@ div_FAC1_denorm:
 
 div_FAC1_denorm_by_bit:
 
-	lda FACOV
+	lda FAC1_mantissa+3
 	and #$01
 	bne div_FAC1_denorm_done           // branch if lowest bit of mantissa is already 1
 
@@ -61,7 +63,6 @@ div_FAC1_denorm_by_bit:
 	ror FAC1_mantissa+1
 	ror FAC1_mantissa+2
 	ror FAC1_mantissa+3
-	ror FACOV
 
 	bcc div_FAC1_denorm_by_bit         // branch always
 
diff --git a/c64/basic/math/div_mantissas.s b/c64/basic/math/div_mantissas.s
index d7771710..06c274aa 100644
--- a/c64/basic/math/div_mantissas.s
+++ b/c64/basic/math/div_mantissas.s
@@ -2,10 +2,10 @@
 // #LAYOUT# *   BASIC_0 #TAKE
 // #LAYOUT# *   *       #IGNORE
 
-// Math package - mantissa division, based on code by Verz
+// Math package - 32-bit mantissa division, based on code by Verz
 //
-// divident: FAC2_mantissa, divisor: FAC1_mantissa, result: FAC2_mantissa, remainder: RESHO
-// temporary storage: INDEX+0, INDEX+1, INDEX+2, INDEX+3, .Y
+// divident: FAC2_mantissa, divisor: FAC1_mantissa (without FACOV), result: FAC2_mantissa, remainder: RESHO
+// temporary storage: INDEX+0, INDEX+1, INDEX+2, INDEX+3
 //
 // RESHO (remainder) should be set to 0 before
 //
@@ -15,7 +15,7 @@
 
 div_mantissas:
 
-	ldx #40                            // repeat for each bit
+	ldx #32                            // repeat for each bit
 
 	// FALLTROUGH
 
@@ -24,13 +24,12 @@ div_mantissas_loop:
 	// Multiply divident by 2, msb -> Carry
 
 	asl FAC2_mantissa+3
-	rol FAC2_mantissa+2	
+	rol FAC2_mantissa+2
 	rol FAC2_mantissa+1
 	rol FAC2_mantissa+0
 
 	// Multiply remainder by 2, lsb <- Carry
 
-	rol RESHO+4
 	rol RESHO+3
 	rol RESHO+2
 	rol RESHO+1
@@ -39,10 +38,6 @@ div_mantissas_loop:
 	// Subtract divisor from the remainder, result to INDEX and .Y
 
 	sec
-	lda RESHO+4
-	sbc FACOV
-	tay
-
 	lda RESHO+3
 	sbc FAC1_mantissa+3
 	sta INDEX+3
@@ -63,9 +58,6 @@ div_mantissas_loop:
 
 	// Save subtraction result as new remainder
 
-	tya
-	sta RESHO+4
-
 	lda INDEX+3
 	sta RESHO+3