User:Qalle/Algorithms

Miscellaneous algorithms that may be useful on the NES.

8-bit unsigned integer to 2 hexadecimal ASCII digits

byte2hex:
    ; in: A = unsigned integer
    ; out: X/A = ASCII digits of sixteens/ones in upper case
    pha
    lsr a
    lsr a
    lsr a
    lsr a
    clc
    jsr nybble2hex
    tax
    pla
    and #%00001111
    jsr nybble2hex
    rts
nybble2hex:
    adc #$30        ; ASCII("0")
    cmp #$3a        ; ASCII("9")+1
    bcc +
    adc #6          ; ASCII("A")-(ASCII("9")+1)-1
+   rts

8-bit unsigned integer to 3 decimal ASCII digits

Source:

byte2dec:
    ; in: A = unsigned integer
    ; out: Y/X/A = ASCII digits of hundreds/tens/ones
    ldy #$2f  ; ASCII("0")-1
    ldx #$3a  ; ASCII("9")+1
    sec
-   iny
    sbc #100
    bcs -
-   dex
    adc #10
    bmi -
    adc #$2f  ; ASCII("0")
    rts