Difference between revisions of "Z80 Routines:Other:DispA"

Revision as of 14:00, 26 October 2009

Unsigned Version

;NOT TESTED. I WILL TEST LATER. SORRY THE CAPS; I HATE THEM; TOO.
;Example: display a=56 as "056".
DispA:
	ld de,OP1	; safe ram to store the ASCII string. Use other one in case you do floating point operations with b_calls
	push de		;we will need it because the output is after the string
	call AtoDec
	ex de,hl
	ld (hl),$00
	pop hl
	b_call(_PutS)
	ret

;Number in a to decimal ASCII
;adapted from 16 bit found in z80 Bits to 8 bit by Galandros
;input: a = number, (de) = decimal ASCII
;destroys af,bc
AtoDec:
	ld	c,-100
	call	Na1
	ld	c,-10
	call	Na1
	ld	c,-1
Na1:	ld	b,'0'-1
Na2:	inc	b
	add	a,c
	jr	c,Na2
	sub	c	;works as add 100/10/1
	ld c,a		;save a
	ld a,b		;ld (de),b  is not a instruction
	ld (de),a
	ld a,c		;restore a
	inc	de
	ret

Signed Version

; DispA
; --------------------------------------------------------------
; Converts a signed integer value to a zero-terminated ASCII
; string representative of that value (using radix 10).
; --------------------------------------------------------------
; INPUTS:
;     HL     Value to convert (two's complement integer).
;     DE     Base address of string destination. (pointer).
; --------------------------------------------------------------
; OUTPUTS:
;     None
; --------------------------------------------------------------
; REGISTERS/MEMORY DESTROYED
; AF HL
; --------------------------------------------------------------

DispA:
   push    de
   push    bc

; Detect sign of HL.
    bit    7, h
    jr     z, _DoConvert

; HL is negative. Output '-' to string and negate HL.
    ld     a, '-'
    ld     (de), a
    inc    de

; Negate HL (using two's complement)
    xor    a
    sub    l
    ld     l, a
    ld     a, 0     ; Note that XOR A or SUB A would disturb CF
    sbc    a, h
    ld     h, a

; Convert HL to digit characters
_DoConvert:
    ld     b, 0     ; B will count character length of number
-   ld     a, 10
    syscall  DivHLByA  ; HL = HL / A, A = remainder
    push   af
    inc    b
    ld     a, h
    or     l
    jr     nz, -

; Retrieve digits from stack
-   pop    af
    or     $30
    ld     (de), a
    inc    de
    djnz   -

; Terminate string with NULL
    xor    a
    ld     (de), a

    pop    bc
    pop    de
    ret

Comments

• This routine uses the common positive-integer radix conversion algorithm of repeatedly dividing a value by the desired radix (base case: the value is zero) and saving the remainders of each division.
• As this algorithm gives the digits in reverse order, they are pushed onto the hardware stack so that subsequently popping them yields the correct order.
• Note that the output string will not be fixed-width.

Example Usage

    ld    hl, -1004
    ld    de, OP1
    call  DispA
    ld    hl, OP1
    syscall  PutS