more multiplication/division work

CREDITS.md

@@ -7,7 +7,6 @@
 * 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 integer division routine
 
 ## for documentation
 

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`        | DONE     |                                                    |
+| `$BA2B`   | `mul_FAC2_FAC1`        | PARTIAL  | needs retest after rework                          |
 | `$BA8C`   | `mov_MEM_FAC2`         | DONE     |                                                    |
 | `$BA90`   | `get_FAC2_via_INDEX`   | NOT DONE |                                                    |
 | `$BAE2`   | `mul10_FAC1`           | DONE     |                                                    |

c64/basic/math/bb12.div_FAC2_FAC1.s

@@ -34,7 +34,7 @@ div_FAC2_FAC1:
 	// Handle special case - dividing 0 by non-zero value
 
 	lda FAC2_exponent
-	beq div_FAC2_FAC1_setexp_quit
+	beq_16 set_FAC1_zero
 
 	// Multiply signs
 	
@@ -42,29 +42,32 @@ div_FAC2_FAC1:
 	eor FAC2_sign
 	sta FAC1_sign
 
-	// Subtract the exponents    XXX what about bias?
+	// Subtract the exponents
+
+	lda #($80 + $08)                   // correction for bias and shifted mantissa
+	sta RESHO+0
+	lda #$00
+	sta RESHO+1
 
 	lda FAC2_exponent
+	jsr muldiv_RESHO_01_add_A
+
+	lda RESHO+0
 	sec
 	sbc FAC1_exponent
 	bcs !+
 
-	// Result too low, set 0 and quit
+	lda RESHO+1
-
+	sbc #$00
-	lda #$00
+	bcc_16 set_FAC1_zero               // result too low, set 0 and quit
-
-div_FAC2_FAC1_setexp_quit:
-
-	sta FAC1_exponent
-	rts
-
 !:
-	adc #$07                           // add 8, as the carry is set here
+	lda RESHO+1
-	bcs_16 set_FAC1_max                // overflow
+	bcc_16 set_FAC1_max                // overflow
-	sta FAC1_exponent
 
 	// Divide the mantissas
 
+	jsr muldiv_RESHO_set_0
+
 	// XXX
 
 
@@ -74,87 +77,5 @@ div_FAC2_FAC1_setexp_quit:
 
 
 
-// XXX adapt, move this to a separate file
-
-// Unsigned integer 32-bit division, based on code by Verz
-// divident: FAC2_mantissa, divisor: FAC1_mantissa, result: FAC2_mantissa, remainder: RESHO
-// temporary storage: INDEX+1, INDEX+2, INDEX+3
-//
-// https://codebase64.org/doku.php?id=base:24bit_division_24-bit_result
-
-// XXX test this, optimize (for temporary storage use .Y, .Z and RESHO+4)
-
-div_mantissas:
-
-	// Preset remainder to 0
-	// XXX should be common with multiplication
-
-	lda #$00
-	sta RESHO+0
-	sta RESHO+1
-	sta RESHO+2
-	sta RESHO+3
-
-	ldx #$32                           // 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+3
-	rol RESHO+2
-	rol RESHO+1
-	rol RESHO+0
-
-	// Subtract divisor to see if it fits in
-
-	lda RESHO+3
-	sec
-	sbc FAC1_mantissa+2
-	sta INDEX+3
-	
-	lda RESHO+2
-	sbc FAC1_mantissa+2
-	sta INDEX+2
-
-	lda RESHO+1
-	sbc FAC1_mantissa+1
-	sta INDEX+1
-
-	lda RESHO+0
-	sbc FAC1_mantissa+0
-	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+1
-	sta RESHO+1
-	lda INDEX+2
-	sta RESHO+2
-	lda INDEX+3
-	sta RESHO+3
-
-	inc FAC2_mantissa+3                // and INCrement result cause divisor fit in 1 times
-
-	// FALLTROUGH
-
-div_mantissas_skip:
-
-	dex
-	bne div_mantissas_loop
-
-	rts
-
-
-
-
-
 
+// XXX use 8-bit divide from here: https://codebase64.org/doku.php?id=base:8bit_divide_8bit_product

c64/basic/math/mul_FAC2_FAC1.s

@@ -17,6 +17,11 @@
 // - https://codebase64.org/doku.php?id=base:kernal_floating_point_mathematics
 //
 
+set_FAC1_zero:
+
+	lda #$00
+	sta FAC1_exponent
+
 mul_FAC2_FAC1_done:
 
 	rts
@@ -39,59 +44,35 @@ mul_FAC2_FAC1:
 	eor FAC2_sign
 	sta FAC1_sign
 	
-	// Check if exponents can be added without overflow/underflow
+	// Add the exponents (subtract the bias)  XXX subroutines should be common with DIV
+
+	jsr muldiv_RESHO_set_0
 
 	lda FAC1_exponent
-	and #$80
+	jsr muldiv_RESHO_01_add_A
-	eor FAC2_exponent
 
-	bmi mul_FAC2_FAC1_add_exponents    // exponent signs are opposite, we can add them safely
+	lda FAC2_exponent
+	jsr muldiv_RESHO_01_add_A
 
-	// Both exponents are either negative (below $80), or both are non-negative ($80 or above),
+	lda RESHO+0
-	// try to add them
+	sbc #($80 - $08)                   // we need to correct double BIAS and shifted mantissa
-	
-	lda FAC1_exponent
-	clc
-	adc FAC2_exponent
-	bpl mul_FAC2_FAC1_sub_exp_bias     // branch if we can add values
-	
-	// We cannot add them, result would over/underflow; set result as
-	// either 0 or maximum possible float
-	
-	lda FAC1_exponent
-	bmi_16 set_FAC1_max
-
-	lda #$00
-	sta FAC1_exponent
-	rts
-	
-mul_FAC2_FAC1_add_exponents:
-	
-	// Add the exponents
-	
-	lda FAC1_exponent
-	clc
-	adc FAC2_exponent
-	
-	// FALLTROUGH
-	
-mul_FAC2_FAC1_sub_exp_bias:
-	
-	sec
-	sbc #$80                           // bias
-	sta FAC1_exponent
-	
-	// Multiply the mantissas - first clear the RESHO temporary area
-
-	lda #$00
 	sta RESHO+0
+	bcs !+
+	lda RESHO+1
+	sbc #$00
+	bcs set_FAC1_zero
 	sta RESHO+1
-	sta RESHO+2
+!:
-	sta RESHO+3
+	lda RESHO+1
-	sta RESHO+4
+	bne_16 set_FAC1_max                // overflow
+
+	lda RESHO+0
+	sta FAC1_exponent
 
 	// Multiply the mantissas
 
+	jsr muldiv_RESHO_set_0
+
 	// XXX maybe we should preserve .X on stack? this will not cost us too much
 
 	lda FACOV

c64/basic/math/muldiv_RESHO_helpers.s

@@ -0,0 +1,29 @@
+// #LAYOUT# STD *       #TAKE
+// #LAYOUT# *   BASIC_0 #TAKE
+// #LAYOUT# *   *       #IGNORE
+
+//
+// Math package - helper routines for RESHO manipulation
+//
+
+
+muldiv_RESHO_set_0:
+
+	lda #$00
+	sta RESHO+0
+	sta RESHO+1
+	sta RESHO+2
+	sta RESHO+3
+	sta RESHO+4
+
+	rts
+
+muldiv_RESHO_01_add_A:
+
+	clc
+	adc RESHO+0
+	sta RESHO+0
+	bcc !+
+	inc RESHO+1
+!:
+	rts