setzerobit

; val: zeropage location for the value
; y: source bit
; x: destination bit

lda val         ; could be "sta val" if value is already in .A
and setbit,y
beq zeroit
setit:
    lda val
    ora setbit,x
    rts
zeroit:
    lda val
    and voidbit,x
    rts

setbit:
byte 1,2,4,8,16,32,64,128               ; values with only one bit set
voidbit:
byte 254,253,251,247,239,223,191,127    ; values with only one bit clear




; Shorter version, just one table
lda setbit,y
and val
beq zeroit
setit:
    lda setbit,x
    ora val
    rts
zeroit:
    lda setbit,x
    eor #$ff
    and val
    rts

setbit:
byte 1,2,4,8,16,32,64,128               ; values with only one bit set