some work towards division

c64/basic/math/bb12.div_FAC2_FAC1.s

@@ -4,13 +4,17 @@
 // #LAYOUT# *   *       #IGNORE
 
 //
-// Math package - divide FAC2 (dividend) by FAC1 (divisor), ignores sign
+// Math package - divide FAC2 (dividend) by FAC1 (divisor)
 //
 // Input:
-// - .A - must load FAC1 exponent ($61) beforehand to set the zero flag
+// - .A - must load FAC1 exponent ($61) beforehand to set the zero flag (but our routine does not need this)
 //
 // Output:
-// - leaves the quotient FAC1 and the remainder in FAC2
+// - FAC1
+//
+// Note:
+// - some documentation suggest this is a division leaving quotient and remainder (left in FAC2),
+//   but it seems (experimentation) that this is not true
 //
 // See also:
 // - [CM64] Computes Mapping the Commodore 64 - page 114
@@ -18,19 +22,61 @@
 // - https://codebase64.org/doku.php?id=base:kernal_floating_point_mathematics
 //
 
-// XXX provide implementation
+// XXX finish the implementation
 
 div_FAC2_FAC1:
+
+	// 'Pamiętaj, cholero - nie dziel przez zero!' - ancient polish proverb
+
+	lda FAC1_exponent
+	beq_16 do_DIVISION_BY_ZERO_error
+
+	// Handle special case - dividing 0 by non-zero value
+
+	lda FAC2_exponent
+	beq div_FAC2_FAC1_setexp_quit
+
+	// Multiply signs
+	
+	lda FAC1_sign
+	eor FAC2_sign
+	sta FAC1_sign
+
+	// Subtract the exponents    XXX what about bias?
+
+	lda FAC2_exponent
+	sec
+	sbc FAC1_exponent
+	bcs !+
+
+	// Result too low, set 0 and quit
+
+	lda #$00
+
+div_FAC2_FAC1_setexp_quit:
+
+	sta FAC1_exponent
+	rts
+
+!:
+	adc #$07                           // add 8, as the carry is set here
+	bcs_16 set_FAC1_max                // overflow
+	sta FAC1_exponent
+
+	// Divide the mantissas
+
+	// XXX
+
+
+
+
 	STUB_IMPLEMENTATION()
 
 
 
+// XXX adapt, move this to a separate file
 
-
-
-// XXX move this to a separate file
-
-// Unsigned integer 32-bit mantissa division, based on code by Verz
+// 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
 //
@@ -106,3 +152,9 @@ div_mantissas_skip:
 	bne div_mantissas_loop
 
 	rts
+
+
+
+
+
+

tools/generate_constants.cc

@@ -58,7 +58,7 @@ std::vector<ConstEntry> GLOBAL_constants =
 	ConstEntry(     "LOG_2", std::log(2.0)        ),
 	ConstEntry( "INV_LOG_2", 1.0 / std::log(2.0)  ),
 
-	// Constants for sine approximation, minimized abs. error, degree 11, from:
+	// Constants for sine approximation, minimized abs. error, degree 11, for [0, pi/2], from:
 	// - https://publik-void.github.io/sin-cos-approximations/
 
 	ConstEntry( "POLY_SIN_1", -2.3794713545277060334805162803882547e-8   ),