work towards printing integers

c64/basic/basic_cold_start.s

@@ -11,6 +11,13 @@ basic_cold_start:
 	lda #<startup_message
 	jsr print_string
 
+	lda #>64738
+	ldx #<64738
+	jsr print_integer	
+
+	lda #$20
+	jsr $ffd2
+	
 	;; Print the rest of the start up message
 	ldx #34
 	jsr print_packed_message
@@ -34,7 +41,4 @@ startup_message:
 	.byte $20,$56,$32,$2e,$30,$2e,$30
 	.byte $0D,$0D
 
-	;; XXX - Hard code in the 38911 for now
-	.byte $33,$38,$39,$31,$31,$20
-	
 	.byte 0

c64/basic/print_integer.s

@@ -0,0 +1,118 @@
+	;; Works similar to $BDCD in original C64 BASIC
+	;; XXX Should eventually get replaced by a more flexible and optimal routine.
+	;; Temp result gets written to $0100-$0104
+print_integer:
+
+	pha
+	txa
+	pha
+
+	;; Clear temporary output
+	lda #$00
+	ldy #5
+*	sta $0100,y
+	dey
+	bpl -
+	
+	pla
+	ldy #23 		; 8 x 3 - 1 = offset of last digit of 128
+lo_loop:	
+	sta $0428,y
+	cmp #$7f
+	bcc bit_clear
+
+	inc $0426
+	
+	;; Bit set, so add the digits
+	pha
+	ldx #2
+	clc
+lo_add_loop:	
+	lda $0102,x
+	adc number_table_lo,y
+	sta $0102,x
+
+	dey
+	dex
+	bpl lo_add_loop
+	pla
+	jmp next_lo_bit	
+	
+bit_clear:
+	dey
+	dey
+	dey
+next_lo_bit:
+	asl
+	cpy #$7f
+	bcc lo_loop	
+
+
+	;; Now do the same for upper byte
+	pla
+	
+	;; Deal with any carries
+	ldx #3
+carry_fix_loop:	
+	lda $0101,x
+	cmp #9
+	bcc +
+	inc $0420
+	inc $0100,x
+	sec
+	sbc #10
+	sta $0101,x
+	jmp carry_fix_loop
+*	dex	
+	bpl carry_fix_loop
+
+post_carry:	
+	
+	;; Got digits.
+	;; Skip leading zeros, and print the resulting number
+
+	ldx #4
+*	lda $0100,x
+	sta $0420,x
+	dex
+	bpl -
+	
+	;; Skip leading zeros
+	ldy #0
+*	lda $0100,y
+	bne found_start_of_number
+	iny
+	cpy #4
+	bne -
+
+found_start_of_number:	
+	;; Print digits
+*	lda $0100,y
+	ora #$30
+	jsr $ffd2
+	iny
+	cpy #5
+	bne -
+	
+	
+	rts
+
+
+number_table_lo:
+	.byte 0,0,1
+	.byte 0,0,2
+	.byte 0,0,4
+	.byte 0,0,8
+	.byte 0,1,6
+	.byte 0,3,2
+	.byte 0,6,4
+	.byte 1,2,8
+number_table_hi:
+	.byte 0,0,2,5,6
+	.byte 0,0,5,1,2
+	.byte 0,1,0,2,4
+	.byte 0,2,0,4,8
+	.byte 0,4,0,9,6
+	.byte 0,8,1,9,2
+	.byte 1,6,3,8,4
+	.byte 3,2,7,6,8