Routine to display large numbers in Z80 created by Miguel Angel Rodriguez Jodar and adapted by me to run on MSX computers

large.asm

; This source code is regulated under the GNU license. Original division
; routine (c)Milos "baze" Bazelides, ( b...@stonline.sk ).
; Rest of code (c)Miguel Angel Rodriguez Jodar ( rodri...@atc.us.es )

;
; Adaptated to run in MSX from Giovanni Nunes
;
CHPUT           equ 0x00a2

                org 0xc000              ; The BASIC program is stored
                                        ; in 0x8000 (32768) address
                                        ; org 32768

Main            proc
                ld de,CADENA

otro_digito     push de
                call Obtener_Resto      ; Get next remainder
                pop de
                add a,'0'               ; Convert to an ASCII digit
                ld (de),a               ; and store it
                inc de
                call Check_Cero         ; Is it the new dividend null?
                jr nz,otro_digito       ; Go to get another digit if not null

                dec de                  ; Fix end address

                ; ld b,d                ; And copy it to BC register
                ; ld c,e
                
                ;
                ; MSX 
                ; 
escribe         ld a,(de)               ; Read number
                cp 0
                ret z                   ; If A is zero, return to BASIC
                call CHPUT              ; write number on screen
                dec de
                jr escribe
                ;
                ; MSX
                ;
                endp

Obtener_Resto   proc
                ld a,(NBYTES)           ; A = number of bytes of the original
                                        ; number. We need number of bits, so we
                                        ; multiply it by 8.
                ld l,a
                ld h,0
                add hl,hl
                add hl,hl
                add hl,hl
                ex de,hl                ; DE = number of bits of the original  
                                        ; number
                ld c,10                 ; C holds the divisor.
                ld hl,NUMERO            ; HL points to the dividend/quotient
                xor a                   ; Reset remainder

buc_div         push hl                 ; This is, esencially, the same
                                        ; algorithm from Milos Bazelides, with
                                        ; the changers detailed above.
                call Mult_2             ; The "old" ADD HL,HL
                pop hl
                rla
                cp c
                jr c,no_incr
                sub c
                call Increm             ; The "old" INC L
no_incr         dec de
                push af
                ld a,d
                or e
                jr z,fin_div
                pop af
                jr buc_div

fin_div         pop af
                ret
                endp

Increm          proc
                ld hl,NUMERO
                inc (hl)
                ret
                endp

Mult_2          proc
                ld hl,NBYTES
                ld b,(hl)
                ld hl,NUMERO

                sla (hl)
                inc hl
                dec b
                ret z

buc_desplaza    rl (hl)
                inc hl
                djnz buc_desplaza

                ret
                endp

Check_Cero      proc
                ld hl,NUMERO
                ld a,(NBYTES)
                ld b,a

check_byte      ld a,(hl)
                or a
                jr nz,no_cero
                inc hl
                djnz check_byte
                xor a
no_cero         ret
                endp

; Variables
NUMERO          ds 255,255              ; 255 bytes filled with the value 255. Little
                                        ; endian notation. This is the largest number this routine can manage
                                        ; (although it's possible that it can deal with 256 byte-wide numbers
NBYTES          db 255                  ; how many bytes comprises our number
                db 0                    ; NULL byte to mark end of the converted number
CADENA          equ $                   ; here will be the ASCII code of the least
                                        ; significant digit of the converted number.