floating point division written, not tested yet

CREDITS.md

@@ -7,6 +7,7 @@
 * Graham - for his PAL/NTSC detection routine
 * enthusi/Onslaught - for his example Turbo Tape 64 compatible loader
 * djmips - for fast 8x8 multiplication routine
+* Verz - for the integer division routine
 
 ## for documentation
 

STATUS.md

@@ -205,7 +205,7 @@ Floating point mathematical routines - not official, but well known and broadly
 | `$BAE2`   | `mul10_FAC1`           | DONE     |                                                    |
 | `$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                          |
+| `$BB12`   | `div_FAC2_FAC1`        | PARTIAL  | not tested yet                                     |
 | `$BBA2`   | `mov_MEM_FAC1`         | DONE     |                                                    |
 | `$BBA6`   | `get_FAC2_via_INDEX`   | NOT DONE |                                                    |
 | `$BBC7`   | `mov_r_FAC1_TMP2`      | PARTIAL  | not fully tested yet                               |

c64/basic/math/bb12.div_FAC2_FAC1.s

@@ -22,7 +22,7 @@
 // - https://codebase64.org/doku.php?id=base:kernal_floating_point_mathematics
 //
 
-// XXX finish the implementation
+// XXX test this code
 
 div_FAC2_FAC1:
 
@@ -68,10 +68,22 @@ div_FAC2_FAC1:
 
 	jsr div_FAC1_denorm
 	jsr muldiv_RESHO_set_0
+	jsr div_mantissas
 
-	// XXX
+	// Copy the result to FAC1 - XXX we probably already have similar code somewhere...
 
+	lda FAC2_mantissa+3
+	sta FAC1_mantissa+3
+	lda FAC2_mantissa+2
+	sta FAC1_mantissa+2
+	lda FAC2_mantissa+1
+	sta FAC1_mantissa+1
+	lda FAC2_mantissa+0
+	sta FAC1_mantissa+0
 
+	lda #$00
+	sta FACOV
 
+	// Normalize and quit
 	
-	STUB_IMPLEMENTATION()
+	jmp normal_FAC1

c64/basic/math/div_mantissas.s

@@ -0,0 +1,79 @@
+// #LAYOUT# STD *       #TAKE
+// #LAYOUT# *   BASIC_0 #TAKE
+// #LAYOUT# *   *       #IGNORE
+
+// Math package - 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
+//
+// RESHO (remainder) should be set to 0 before
+//
+// see https://codebase64.org/doku.php?id=base:24bit_division_24-bit_result
+
+// XXX test this
+
+div_mantissas:
+
+	ldx #40                            // repeat for each bit
+
+	// FALLTROUGH
+
+div_mantissas_loop:
+
+	// Multiply divident by 2, msb -> Carry
+
+	asl FAC2_mantissa+3
+	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
+	rol RESHO+0
+
+	// Subtract divisor to see if it fits in
+
+	lda RESHO+4
+	sec
+	sbc FAC1_mantissa+3
+	sta INDEX+3
+
+	lda RESHO+3
+	sbc FAC1_mantissa+2
+	sta INDEX+2
+
+	lda RESHO+2
+	sbc FAC1_mantissa+1
+	sta INDEX+1
+
+	lda RESHO+1
+	sbc FAC1_mantissa+0
+	sta INDEX+0
+
+	lda RESHO+0
+	sbc #$00
+	bcc div_mantissas_skip             // if Carry is not set then divisor did not fit in yet
+
+	sta RESHO+0                        // else save substraction result as new remainder,
+	lda INDEX+0
+	sta RESHO+1
+	lda INDEX+1
+	sta RESHO+2
+	lda INDEX+3
+	sta RESHO+4
+
+	inc FAC2_mantissa+3                // and INCrement result cause divisor fit in 1 times
+
+	// FALLTROUGH
+
+div_mantissas_skip:
+
+	dex
+	bne div_mantissas_loop
+
+	rts