prog8/lib/c64lib.ill

; IL65 definitions for the Commodore-64
; Including memory registers, I/O registers, Basic and Kernel subroutines, utility subroutines.
;
; Written by Irmen de Jong (irmen@razorvine.net)
; License: GNU GPL 3.0, see LICENSE
;
; indent format: TABS, size=8


output raw

~ c64 {
		memory  SCRATCH_ZP1	= $02		; scratch register #1 in ZP
		memory  SCRATCH_ZP2	= $03		; scratch register #2 in ZP

		memory  .byte COLOR	= $0286		; cursor color
		memory  .word CINV	= $0314		; IRQ vector

; ---- VIC-II registers ----

		memory  SP0X		= $d000
		memory  SP0Y		= $d001
		memory  SP1X		= $d002
		memory  SP1Y		= $d003
		memory  SP2X		= $d004
		memory  SP2Y		= $d005
		memory  SP3X		= $d006
		memory  SP3Y		= $d007
		memory  SP4X		= $d008
		memory  SP4Y		= $d009
		memory  SP5X		= $d00a
		memory  SP5Y		= $d00b
		memory  SP6X		= $d00c
		memory  SP6Y		= $d00d
		memory  SP7X		= $d00e
		memory  SP7Y		= $d00f

		memory  MSIGX		= $d010
		memory  SCROLY		= $d011
		memory  RASTER		= $d012
		memory  LPENX		= $d013
		memory  LPENY		= $d014
		memory  SPENA		= $d015
		memory  SCROLX		= $d016
		memory  YXPAND		= $d017
		memory  VMCSB		= $d018
		memory  VICIRQ		= $d019
		memory  IREQMASK	= $d01a
		memory  SPBGPR		= $d01b
		memory  SPMC		= $d01c
		memory  XXPAND		= $d01d
		memory  SPSPCL		= $d01e
		memory  SPBGCL		= $d01f

		memory  EXTCOL		= $d020		; border color
		memory  BGCOL0		= $d021		; screen color
		memory  BGCOL1		= $d022
		memory  BGCOL2		= $d023
		memory  BGCOL4		= $d024
		memory  SPMC0		= $d025
		memory  SPMC1		= $d026
		memory  SP0COL		= $d027
		memory  SP1COL		= $d028
		memory  SP2COL		= $d029
		memory  SP3COL		= $d02a
		memory  SP4COL		= $d02b
		memory  SP5COL		= $d02c
		memory  SP6COL		= $d02d
		memory  SP7COL		= $d02e

; ---- end of VIC-II registers ----

; ---- C64 basic and kernal ROM float constants and functions ----

		; note: the fac1 and fac2 are working registers and take 6 bytes each,
		; floats in memory  (and rom) are stored in 5-byte MFLPT packed format.

		; constants in five-byte "mflpt" format in the BASIC ROM
		memory  .float	FL_PIVAL	= $aea8  ; 3.1415926...
		memory  .float	FL_N32768	= $b1a5  ; -32768
		memory  .float	FL_FONE		= $b9bc  ; 1
		memory  .float	FL_SQRHLF	= $b9d6  ; SQR(2) / 2
		memory  .float	FL_SQRTWO	= $b9db  ; SQR(2)
		memory  .float	FL_NEGHLF	= $b9e0  ; -.5
		memory  .float	FL_LOG2		= $b9e5  ; LOG(2)
		memory  .float	FL_TENC		= $baf9  ; 10
		memory  .float	FL_NZMIL	= $bdbd  ; 1e9 (1 billion)
		memory  .float	FL_FHALF	= $bf11  ; .5
		memory  .float	FL_LOGEB2	= $bfbf  ; 1 / LOG(2)
		memory  .float	FL_PIHALF	= $e2e0  ; PI / 2
		memory  .float	FL_TWOPI	= $e2e5  ; 2 * PI
		memory  .float	FL_FR4		= $e2ea  ; .25


; note: fac1/2 might get clobbered even if not mentioned in the function's name.
; note: for subtraction and division, the left operand is in fac2, the right operand in fac1.

; checked functions below:
sub	MOVFM		(mflpt: AY) -> (A?, Y?)		= $bba2		; load mflpt value from memory  in A/Y into fac1
sub	FREADMEM	() -> (A?, Y?)			= $bba6		; load mflpt value from memory  in $22/$23 into fac1
sub	CONUPK		(mflpt: AY) -> (A?, Y?)		= $ba8c		; load mflpt value from memory  in A/Y into fac2
sub	FAREADMEM	() -> (A?, Y?)			= $ba90		; load mflpt value from memory  in $22/$23 into fac2
sub	MOVFA		() -> (A?, X?)			= $bbfc		; copy fac2 to fac1
sub	MOVAF		() -> (A?, X?)			= $bc0c		; copy fac1 to fac2  (rounded)
sub	MOVEF		() -> (A?, X?)			= $bc0f		; copy fac1 to fac2
sub	FTOMEMXY	(mflpt: XY) -> (A?, Y?)		= $bbd4		; store fac1 to memory  X/Y as 5-byte mflpt
sub	FTOSWORDYA	() -> (Y, A, X?)		= $b1aa		; fac1-> signed word in Y/A (might throw ILLEGAL QUANTITY)
	; use c64util.FTOSWRDAY to get A/Y output (lo/hi switched to normal order)
sub	GETADR		() -> (Y, A, X?)		= $b7f7		; fac1 -> unsigned word in Y/A (might throw ILLEGAL QUANTITY)
	; (result also in $14/15) use c64util.GETADRAY to get A/Y output (lo/hi switched to normal order)
sub	QINT		() -> (A?, X?, Y?)		= $bc9b		; fac1 -> 4-byte signed integer in 98-101 ($62-$65), with the MSB FIRST.
sub	AYINT		() -> (A?, X?, Y?)		= $b1bf		; fac1-> signed word in 100-101 ($64-$65) MSB FIRST. (might throw ILLEGAL QUANTITY)
sub	GIVAYF		(lo: Y, hi: A) -> (A?, X?, Y?)	= $b391		; signed word in Y/A -> float in fac1
	; use c64util.GIVAYFAY to use A/Y input (lo/hi switched to normal order)
; there is also c64util.GIVUAYF - unsigned word in A/Y (lo/hi) to fac1
; there is also c64util.FREADS32  that reads from 98-101 ($62-$65) MSB FIRST
; there is also c64util.FREADUS32  that reads from 98-101 ($62-$65) MSB FIRST
; there is also c64util.FREADS24AXY  that reads signed int24 into fac1 from A/X/Y (lo/mid/hi bytes)
sub	FREADUY		(ubyte: Y) -> (A?, X?, Y?)	= $b3a2		; 8 bit unsigned Y -> float in fac1
sub	FREADSA		(sbyte: A) -> (A?, X?, Y?)	= $bc3c		; 8 bit signed A -> float in fac1
sub	FREADSTR	(len: A) -> (A?, X?, Y?)	= $b7b5		; str -> fac1, $22/23 must point to string, A=string length
sub	FPRINTLN	() -> (A?, X?, Y?)		= $aabc		; print string of fac1, on one line (= with newline)
sub	FOUT		() -> (AY, X?)			= $bddd		; fac1 -> string, address returned in AY ($0100)

sub	FADDH		() -> (A?, X?, Y?)		= $b849		; fac1 += 0.5, for rounding- call this before INT
sub	MUL10		() -> (A?, X?, Y?)		= $bae2		; fac1 *= 10
sub	DIV10		() -> (A?, X?, Y?)		= $bafe		; fac1 /= 10 , CAUTION: result is always positive!
sub	FCOMP		(mflpt: AY) -> (A, X?, Y?)	= $bc5b		; A = compare fac1 to mflpt in A/Y, 0=equal 1=fac1 is greater, 255=fac1 is less than

sub	FADDT		() -> (A?, X?, Y?)		= $b86a		; fac1 += fac2
sub	FADD		(mflpt: AY) -> (A?, X?, Y?)	= $b867		; fac1 += mflpt value from A/Y
sub	FSUBT		() -> (A?, X?, Y?)		= $b853		; fac1 = fac2-fac1   mind the order of the operands
sub	FSUB		(mflpt: AY) -> (A?, X?, Y?)	= $b850		; fac1 = mflpt from A/Y - fac1
sub	FMULTT 		() -> (A?, X?, Y?)		= $ba2b		; fac1 *= fac2
sub	FMULT		(mflpt: AY) -> (A?, X?, Y?)	= $ba28		; fac1 *= mflpt value from A/Y
sub	FDIVT 		() -> (A?, X?, Y?)		= $bb12		; fac1 = fac2/fac1   mind the order of the operands
sub	FDIV  		(mflpt: AY) -> (A?, X?, Y?)	= $bb0f		; fac1 = mflpt in A/Y / fac1
sub	FPWRT		() -> (A?, X?, Y?)		= $bf7b		; fac1 = fac2 ** fac1
sub	FPWR		(mflpt: AY) -> (A?, X?, Y?)	= $bf78		; fac1 = fac2 ** mflpt from A/Y

sub	NOTOP		() -> (A?, X?, Y?)		= $aed4		; fac1 = NOT(fac1)
sub	INT		() -> (A?, X?, Y?)		= $bccc		; INT() truncates, use FADDH first to round instead of trunc
sub	LOG		() -> (A?, X?, Y?)		= $b9ea		; fac1 = LN(fac1)  (natural log)
sub	SGN		() -> (A?, X?, Y?)		= $bc39		; fac1 = SGN(fac1), result of SIGN (-1, 0 or 1)
sub	SIGN		() -> (A)			= $bc2b		; SIGN(fac1) to A, $ff, $0, $1 for negative, zero, positive
sub	ABS		() -> ()			= $bc58		; fac1 = ABS(fac1)
sub	SQR		() -> (A?, X?, Y?)		= $bf71		; fac1 = SQRT(fac1)
sub	EXP		() -> (A?, X?, Y?)		= $bfed		; fac1 = EXP(fac1)  (e ** fac1)
sub	NEGOP		() -> (A?)			= $bfb4		; switch the sign of fac1
sub	RND		() -> (A?, X?, Y?)		= $e097		; fac1 = RND()   (use RNDA instead)
sub	RNDA		(A) -> (A?, X?, Y?)		= $e09a		; fac1 = RND(A)
sub	COS		() -> (A?, X?, Y?)		= $e264		; fac1 = COS(fac1)
sub	SIN		() -> (A?, X?, Y?)		= $e26b		; fac1 = SIN(fac1)
sub	TAN		() -> (A?, X?, Y?)		= $e2b4		; fac1 = TAN(fac1)
sub	ATN		() -> (A?, X?, Y?)		= $e30e		; fac1 = ATN(fac1)


; ---- C64 basic routines ----

sub	CLEARSCR	() -> (A?, X?, Y?)		= $E544		; clear the screen
sub	HOMECRSR	() -> (A?, X?, Y?)		= $E566		; cursor to top left of screen


; ---- end of C64 basic routines ----



; ---- C64 kernal routines ----

sub	IRQDFRT  () -> (A?, X?, Y?)			= $EA31		; default IRQ routine
sub	IRQDFEND () -> (A?, X?, Y?)			= $EA81		; default IRQ end/cleanup
sub	CINT     () -> (A?, X?, Y?)			= $FF81		; (alias: SCINIT) initialize screen editor and video chip
sub	IOINIT   () -> (A?, X?)				= $FF84		; initialize I/O devices (CIA, SID, IRQ)
sub	RAMTAS   () -> (A?, X?, Y?)			= $FF87		; initialize RAM, tape buffer, screen
sub	RESTOR   () -> (A?, X?, Y?)			= $FF8A		; restore default I/O vectors
sub	VECTOR   (dir: SC, userptr: XY) -> (A?, Y?)	= $FF8D		; read/set I/O vector table
sub	SETMSG   (value: A) -> ()			= $FF90		; set Kernal message control flag
sub	SECOND   (address: A) -> (A?)			= $FF93		; (alias: LSTNSA) send secondary address after LISTEN
sub	TKSA     (address: A) -> (A?)			= $FF96		; (alias: TALKSA) send secondary address after TALK
sub	MEMTOP   (dir: SC, address: XY) -> (XY)		= $FF99		; read/set top of memory  pointer
sub	MEMBOT   (dir: SC, address: XY) -> (XY)		= $FF9C		; read/set bottom of memory  pointer
sub	SCNKEY   () -> (A?, X?, Y?)			= $FF9F		; scan the keyboard
sub	SETTMO   (timeout: A) -> ()			= $FFA2		; set time-out flag for IEEE bus
sub	ACPTR    () -> (A)				= $FFA5		; (alias: IECIN) input byte from serial bus
sub	CIOUT    (byte: A) -> ()			= $FFA8		; (alias: IECOUT) output byte to serial bus
sub	UNTLK    () -> (A?)				= $FFAB		; command serial bus device to UNTALK
sub	UNLSN    () -> (A?)				= $FFAE		; command serial bus device to UNLISTEN
sub	LISTEN   (device: A) -> (A?)			= $FFB1		; command serial bus device to LISTEN
sub	TALK     (device: A) -> (A?)			= $FFB4		; command serial bus device to TALK
sub	READST   () -> (A)				= $FFB7		; read I/O status word
sub	SETLFS   (logical: A, device: X, address: Y) -> () = $FFBA	; set logical file parameters
sub	SETNAM   (namelen: A, filename: XY) -> ()	= $FFBD		; set filename parameters
sub	OPEN     () -> (A?, X?, Y?)			= $FFC0		; (via 794 ($31A)) open a logical file
sub	CLOSE    (logical: A) -> (A?, X?, Y?)		= $FFC3		; (via 796 ($31C)) close a logical file
sub	CHKIN    (logical: X) -> (A?, X?)		= $FFC6		; (via 798 ($31E)) define an input channel
sub	CHKOUT   (logical: X) -> (A?, X?)		= $FFC9		; (via 800 ($320)) define an output channel
sub	CLRCHN   () -> (A?, X?)				= $FFCC		; (via 802 ($322)) restore default devices
sub	CHRIN    () -> (A, Y?)				= $FFCF		; (via 804 ($324)) input a character (for keyboard, read a whole line from the screen) A=byte read.
sub	CHROUT   (char: A) -> ()			= $FFD2		; (via 806 ($326)) output a character
sub	LOAD     (verify: A, address: XY) -> (SC, A, X, Y) = $FFD5	; (via 816 ($330)) load from device
sub	SAVE     (zp_startaddr: A, endaddr: XY) -> (SC, A) = $FFD8	; (via 818 ($332)) save to a device
sub	SETTIM   (low: A, middle: X, high: Y) -> ()	= $FFDB		; set the software clock
sub	RDTIM    () -> (A, X, Y)			= $FFDE		; read the software clock
sub	STOP     () -> (SZ, SC, A?, X?)			= $FFE1		; (via 808 ($328)) check the STOP key
sub	GETIN    () -> (A, X?, Y?)			= $FFE4		; (via 810 ($32A)) get a character
sub	CLALL    () -> (A?, X?)				= $FFE7		; (via 812 ($32C)) close all files
sub	UDTIM    () -> (A?, X?)				= $FFEA		; update the software clock
sub	SCREEN   () -> (X, Y)				= $FFED		; read number of screen rows and columns
sub	PLOT     (dir: SC, col: X, row: Y) -> (X, Y)	= $FFF0		; read/set position of cursor on screen
sub	IOBASE   () -> (X, Y)				= $FFF3		; read base address of I/O devices

; ---- end of C64 kernal routines ----

		memory  .word	NMI_VEC		= $FFFA  ; nmi vector, set by the kernal if banked in
		memory  .word	RESET_VEC	= $FFFC  ; reset vector, set by the kernal if banked in
		memory  .word	IRQ_VEC		= $FFFE  ; interrupt vector, set by the kernal if banked in

}


~ c64util {

sub  init_system  () -> (A?, X?, Y?)  {
	; ---- initializes the machine to a sane starting state
	; This means that the BASIC, KERNAL and CHARGEN ROMs are banked in,
	; the VIC, SID and CIA chips are reset, screen is cleared, and the default IRQ is set.
	; Also a different color scheme is chosen to identify ourselves a little.
	asm  {
		sei
		cld
		lda  #%00101111
		sta  $00
		lda  #%00100111
		sta  $01
		jsr  c64.IOINIT
		jsr  c64.RESTOR
		jsr  c64.CINT
		lda  #6
		sta  c64.EXTCOL
		lda  #7
		sta  c64.COLOR
		lda  #0
		sta  c64.BGCOL0
		tax
		tay
		clc
		clv
		cli
		rts
	}
}


sub  FREADS32  () -> (A?, X?, Y?)  {
	; ---- fac1 = signed int32 from $62-$65 big endian (MSB FIRST)
	asm {
		lda  $62
		eor  #$ff
		asl  a
		lda  #0
		ldx  #$a0
		jmp  $bc4f		; internal BASIC routine
	}
}

sub  FREADUS32  () -> (A?, X?, Y?)  {
	; ---- fac1 = uint32 from $62-$65 big endian (MSB FIRST)
	asm {
		sec
		lda  #0
		ldx  #$a0
		jmp  $bc4f		; internal BASIC routine
	}
}

sub  FREADS24AXY  (lo: A, mid: X, hi: Y) -> (A?, X?, Y?)  {
	; ---- fac1 = signed int24 (A/X/Y contain lo/mid/hi bytes)
	;      note: there is no FREADU24AXY (unsigned), use FREADUS32 instead.
	asm {
		sty  $62
		stx  $63
		sta  $64
		lda  $62
		eor  #$FF
		asl  a
		lda  #0
		sta  $65
		ldx  #$98
		jmp  $bc4f		; internal BASIC routine
	}
}

sub  GIVUAYF  (uword: AY) -> (A?, X?, Y?)  {
	; ---- unsigned 16 bit word in A/Y (lo/hi) to fac1
	asm {
		sty  $62
		sta  $63
		ldx  #$90
		sec
		jmp  $bc49		; internal BASIC routine
	}
}

sub  GIVAYFAY  (sword: AY) -> (A?, X?, Y?)  {
	; ---- signed 16 bit word in A/Y (lo/hi) to float in fac1
	asm {
		sta  c64.SCRATCH_ZP1
		tya
		ldy  c64.SCRATCH_ZP1
		jmp  c64.GIVAYF		; this uses the inverse order, Y/A
	}
}

sub  FTOSWRDAY  () -> (AY, X?)  {
	; ---- fac1 to signed word in A/Y
	asm {
		jsr  c64.FTOSWORDYA	; note the inverse Y/A order
		sta  c64.SCRATCH_ZP1
		tya
		ldy  c64.SCRATCH_ZP1
		rts
	}
}

sub  GETADRAY  () -> (AY, X?)  {
	; ---- fac1 to unsigned word in A/Y
	asm {
		jsr  c64.GETADR		; this uses the inverse order, Y/A
		sta  c64.SCRATCH_ZP1
		tya
		ldy  c64.SCRATCH_ZP1
		rts
	}
}

sub  print_string (address: XY) -> (A?, Y?)  {
	; ---- print null terminated string from X/Y
	asm {
		stx  c64.SCRATCH_ZP1
		sty  c64.SCRATCH_ZP2
		ldy  #0
-               lda  (c64.SCRATCH_ZP1),y
		beq  +
		jsr  c64.CHROUT
		iny
		bne  -
+		rts
	}
}

sub  print_pstring  (address: XY) -> (A?, X?, Y)  {
	; ---- print pstring (length as first byte) from X/Y, returns str len in Y
	asm {
		stx  c64.SCRATCH_ZP1
		sty  c64.SCRATCH_ZP2
		ldy  #0
		lda  (c64.SCRATCH_ZP1),y
		beq  +
		tax
-		iny
		lda  (c64.SCRATCH_ZP1),y
		jsr  c64.CHROUT
		dex
		bne  -
+		rts 			; output string length is in Y
	}
}

sub  print_pimmediate  () -> ()  {
	; ---- print pstring in memory  immediately following the subroutine fast call instruction
	; note that the clobbered registers (A,X,Y) are not listed ON PURPOSE
	asm {
		tsx
		lda  $102,x
		tay			; put high byte in y
		lda  $101,x
		tax			; and low byte in x.
		inx
		bne  +
		iny
+		jsr  print_pstring	; print string in XY, returns string length in y.
		tya
		tsx
		clc
		adc  $101,x		; add content of 1st (length) byte to return addr.
		bcc  +      		; if that made the low byte roll over to 00,
		inc  $102,x		; then increment the high byte too.
+		clc
		adc  #1			; now add 1 for the length byte itself.
		sta  $101,x
		bne  +			; if that made it (the low byte) roll over to 00,
		inc  $102,x		; increment the high byte of the return addr too.
+		rts
	}
}

sub  byte2decimal  (ubyte: A) -> (Y, X, A)  {
	; ---- A to decimal string in Y/X/A  (100s in Y, 10s in X, 1s in A)
	asm {
		ldy  #$2f
		ldx  #$3a
		sec
-               iny
		sbc  #100
		bcs  -
-               dex
		adc  #10
		bmi  -
		adc  #$2f
		rts
	}
}

sub  byte2hex  (ubyte: A) -> (X, Y, A?)  {
	; ---- A to hex string in XY (first hex char in X, second hex char in Y)
	asm {
		pha
		and  #$0f
		tax
		ldy  hex_digits,x
		pla
		lsr  a
		lsr  a
		lsr  a
		lsr  a
		tax
		lda  hex_digits,x
		tax
		rts

hex_digits	.text "0123456789abcdef"	; can probably be reused for other stuff as well
	}
}

		; var  .array(4)  word2hex_output_array    @todo support to use array/matrix type by address
		var  .text      word2hex_output = "123"   ; 0-terminated, 4 bytes total @todo remove if array works
sub  word2hex  (word: XY) -> (A?, X?, Y?)  {
	; ---- convert 16 bit word in X/Y into hexadecimal string into memory  'word2hex_output'
	asm {
		stx  c64.SCRATCH_ZP2
		tya
		jsr  byte2hex
		stx  word2hex_output
		sty  word2hex_output+1
		lda  c64.SCRATCH_ZP2
		jsr  byte2hex
		stx  word2hex_output+2
		sty  word2hex_output+3
		rts
	}
}


		var  .array(3)  word2bcd_bcdbuff
sub  word2bcd  (word: XY) -> (A?, X?)  {
	; Convert an 16 bit binary value to BCD
	;
	; This function converts a 16 bit binary value in X/Y into a 24 bit BCD. It
	; works by transferring one bit a time from the source and adding it
	; into a BCD value that is being doubled on each iteration. As all the
	; arithmetic is being done in BCD the result is a binary to decimal
	; conversion.
	asm {
		stx  c64.SCRATCH_ZP1
		sty  c64.SCRATCH_ZP2
		sed				; switch to decimal mode
		lda  #0				; ensure the result is clear
		sta  word2bcd_bcdbuff+0
		sta  word2bcd_bcdbuff+1
		sta  word2bcd_bcdbuff+2
		ldx  #16			; the number of source bits

-		asl  c64.SCRATCH_ZP1		; shift out one bit
		rol  c64.SCRATCH_ZP2
		lda  word2bcd_bcdbuff+0		; and add into result
		adc  word2bcd_bcdbuff+0
		sta  word2bcd_bcdbuff+0
		lda  word2bcd_bcdbuff+1		; propagating any carry
		adc  word2bcd_bcdbuff+1
		sta  word2bcd_bcdbuff+1
		lda  word2bcd_bcdbuff+2		; ... thru whole result
		adc  word2bcd_bcdbuff+2
		sta  word2bcd_bcdbuff+2
		dex				; and repeat for next bit
		bne  -
		cld				; back to binary
		rts
	}
}


		var  .array(5)  word2decimal_output
sub  word2decimal  (word: XY) -> (A?, X?, Y?)  {
	; ---- convert 16 bit word in X/Y into decimal string into memory  'word2decimal_output'
	asm {
		jsr  word2bcd
		lda  word2bcd_bcdbuff+2
		clc
		adc  #'0'
		sta  word2decimal_output
		ldy  #1
		lda  word2bcd_bcdbuff+1
		jsr  +
		lda  word2bcd_bcdbuff+0

+		pha
		lsr  a
		lsr  a
		lsr  a
		lsr  a
		clc
		adc  #'0'
		sta  word2decimal_output,y
		iny
		pla
		and  #$0f
		adc  #'0'
		sta  word2decimal_output,y
		iny
		rts
	}
}

sub  print_byte_decimal0  (ubyte: A) -> (A?, X?, Y?)  {
	; ---- print the byte in A in decimal form, with left padding 0s (3 positions total)
	asm {
		jsr  byte2decimal
		pha
		tya
		jsr  c64.CHROUT
		txa
		jsr  c64.CHROUT
		pla
		jmp  c64.CHROUT
	}
}

sub  print_byte_decimal  (ubyte: A) -> (A?, X?, Y?)  {
	; ---- print the byte in A in decimal form, without left padding 0s
	asm {
		jsr  byte2decimal
		pha
		cpy  #'0'
		bne  _print_hundreds
		cpx  #'0'
		bne  _print_tens
		pla
		jmp  c64.CHROUT
_print_hundreds	tya
		jsr  c64.CHROUT
_print_tens	txa
		jsr  c64.CHROUT
		pla
		jmp  c64.CHROUT
	}
}

sub  print_byte_hex  (prefix: SC, ubyte: A) -> (A?, X?, Y?)  {
	; ---- print the byte in A in hex form (if Carry is set, a radix prefix '$' is printed as well)
	asm {
		bcc  +
		pha
		lda  #'$'
		jsr  c64.CHROUT
		pla
+		jsr  byte2hex
		txa
		jsr  c64.CHROUT
		tya
		jmp  c64.CHROUT
	}
}

sub print_word_hex  (prefix: SC, word: XY) -> (A?, X?, Y?)  {
	; ---- print the (unsigned) word in X/Y in hexadecimal form (4 digits)
	;      (if Carry is set, a radix prefix '$' is printed as well)
	asm {
		stx  c64.SCRATCH_ZP1
		tya
		jsr  print_byte_hex
		lda  c64.SCRATCH_ZP1
		clc
		jmp  print_byte_hex
	}
}


sub  print_word_decimal0  (word: XY) -> (A?, X?, Y?)  {
	; ---- print the (unsigned) word in X/Y in decimal form, with left padding 0s (5 positions total)
	asm {
		jsr  word2decimal
		lda  word2decimal_output
		jsr  c64.CHROUT
		lda  word2decimal_output+1
		jsr  c64.CHROUT
		lda  word2decimal_output+2
		jsr  c64.CHROUT
		lda  word2decimal_output+3
		jsr  c64.CHROUT
		lda  word2decimal_output+4
		jmp  c64.CHROUT
	}
}


sub  print_word_decimal  (word: XY) -> (A?, X? Y?)  {
	; ---- print the word in X/Y in decimal form, without left padding 0s
	asm {
		jsr  word2decimal
		ldy  #0
		lda  word2decimal_output
		cmp  #'0'
		bne  _pr_decimal
		iny
		lda  word2decimal_output+1
		cmp  #'0'
		bne  _pr_decimal
		iny
		lda  word2decimal_output+2
		cmp  #'0'
		bne  _pr_decimal
		iny
		lda  word2decimal_output+3
		cmp  #'0'
		bne  _pr_decimal
		iny

_pr_decimal
		lda  word2decimal_output,y
		jsr  c64.CHROUT
		iny
		cpy  #5
		bcc  _pr_decimal
		rts
	}
}


; @todo string to 32 bit unsigned integer http://www.6502.org/source/strings/ascii-to-32bit.html


sub  input_chars  (buffer: AX) -> (A?, Y)  {
	; ---- Input a string (max. 80 chars) from the keyboard.
	;      It assumes the keyboard is selected as I/O channel!!

	asm {
		sta  c64.SCRATCH_ZP1
		stx  c64.SCRATCH_ZP2
		ldy  #0				; char counter = 0
-		jsr  c64.CHRIN
		cmp  #$0d			; return (ascii 13) pressed?
		beq  +				; yes, end.
		sta  (c64.SCRATCH_ZP1),y	; else store char in buffer
		iny
		bne  -
+		lda  #0
		sta  (c64.SCRATCH_ZP1),y	; finish string with 0 byte
		rts

	}
}

;sub  memcopy_basic  () -> (A?, X?, Y?)  {
;	; ---- copy a memory block by using a BASIC ROM routine  @todo fix code
;	; it calls a function from the basic interpreter, so:
;	;       - BASIC ROM must be banked in
;	;       - the source block must be readable (so no RAM hidden under BASIC, Kernal, or I/O)
;	;       - the target block must be writable (so no RAM hidden under I/O)
;	; higher addresses are copied first, so:
;	;       - moving data to higher addresses works even if areas overlap
;	;       - moving data to lower addresses only works if areas do not overlap
;	; @todo fix this
;	asm {
;		lda  #<src_start
;		ldx  #>src_start
;		sta  $5f
;		stx  $60
;		lda  #<src_end
;		ldx  #>src_end
;		sta  $5a
;		stx  $5b
;		lda  #<(target_start + src_end - src_start)
;		ldx  #>(target_start + src_end - src_start)
;		sta  $58
;		stx  $59
;		jmp  $a3bf
;	}
;}

; macro version of the above memcopy_basic routine:	@todo macro support?
; MACRO PARAMS src_start, src_end, target_start
;		lda  #<src_start
;		ldx  #>src_start
;		sta  $5f
;		stx  $60
;		lda  #<src_end
;		ldx  #>src_end
;		sta  $5a
;		stx  $5b
;		lda  #<(target_start + src_end - src_start)
;		ldx  #>(target_start + src_end - src_start)
;		sta  $58
;		stx  $59
;		jsr  $a3bf



}