implemented 2 more simple math routines

2020-02-01 20:52:00 +01:00
1 parent 51064f6b70
commit a2cd07a94c
@@ -0,0 +1,51 @@
+// #LAYOUT# STD *       #TAKE
+// #LAYOUT# *   BASIC_0 #TAKE
+// #LAYOUT# *   *       #IGNORE
+
+//
+// Math package - move FAC1 to FAC2
+//
+// Output (all found by experimentation):
+// - .A - FAC1 exponent
+// - .X - always 0
+//
+// Preserves (found by experimentation):
+// - .Y
+//
+// Note:
+// - observed that original ROM always clears FACOV, not sure why
+//
+// See also:
+// - [CM64] Computes Mapping the Commodore 64 - page 115
+// - https://www.c64-wiki.com/wiki/BASIC-ROM
+// - https://www.c64-wiki.com/wiki/Floating_point_arithmetic
+//
+
+MOVFA:
+
+	// Copy the exponent
+	lda FAC1_exponent
+	sta FAC2_exponent
+	beq !+                             // for 0 no need to copy mantissa and sign
+
+	// Copy the mantissa
+	lda FAC1_mantissa+0
+	sta FAC2_mantissa+0
+	lda FAC1_mantissa+1
+	sta FAC2_mantissa+1
+	lda FAC1_mantissa+2
+	sta FAC2_mantissa+2
+	lda FAC1_mantissa+3
+	sta FAC2_mantissa+3
+
+	// Copy the sign
+	lda FAC1_sign
+	sta FAC2_sign
+
+	lda FAC1_exponent
+!:
+	// Duplicate the original ROM behaviour
+	ldx #$00
+	stx FACOV
+
+	rts
@@ -21,7 +21,7 @@

 // XXX test this

-MOVMF:
+MOVFM:

 	// Checked in the available documentation:
 	// - https://www.c64-wiki.com/wiki/Floating_point_arithmetic
@@ -43,7 +43,7 @@ ROUND:
 	inc FAC1_exponent
 	bne round_zero_FACOV

-	// If w are here, it means the exponent wrapped around to $00; put it back to $FF
+	// If we are here, it means the exponent wrapped around to $00; put it back to $FF

 	dec FAC1_exponent

@@ -4,4 +4,4 @@

 // Just a compatibility jump - our routine is longer than original one

-	jmp MOVMF
+	jmp MOVFM
@@ -0,0 +1,22 @@
+// #LAYOUT# STD *       #TAKE
+// #LAYOUT# *   BASIC_0 #TAKE
+// #LAYOUT# *   *       #IGNORE
+
+//
+// Math package - round and move FAC1 to FAC2
+//
+// Output:
+// - .A - FAC1 exponent
+//
+// See also:
+// - [CM64] Computes Mapping the Commodore 64 - page 115
+// - https://www.c64-wiki.com/wiki/BASIC-ROM
+// - https://www.c64-wiki.com/wiki/Floating_point_arithmetic
+//
+
+MOVAF:
+
+	// First round FAC1
+	jsr ROUND
+
+	// FALLTROUGH to MOVFA
@@ -0,0 +1,3 @@
+This is an important floating point math routine, documented in many places.
+
+XXX - try to find real-life example
@@ -0,0 +1,7 @@
+// #LAYOUT# STD *       #TAKE
+// #LAYOUT# *   BASIC_0 #TAKE
+// #LAYOUT# *   *       #IGNORE
+
+// Just a compatibility jump - our routine is longer than original one
+
+	jmp MOVFA
@@ -0,0 +1,3 @@
+This is an important floating point math routine, documented in many places.
+
+XXX - try to find real-life example