sumBits:
    ;b=byte
    ld d,0
    ld a,b          ;4
    and %01010101   ;7
    jr z,_nexthalf  ;12/7
    ld c,a          ;4
    jp pe,_e1       ;10
    and %00001111   ;7
    jr z,_oz1       ;12/7
    jp pe,_oe1      ;10
    ld a,c          ;4
    and %11110000   ;7
    jr z,_oz1       ;12/7
    inc d
    jp _nexthalf:   ;10
_oe1:
    inc d           ;4
    inc d           ;4
_oz1:
    inc d           ;4
    jp _nexthalf    ;10
_e1:
    and %00001111
    jr z,_ez1
    jp po,_ez1
    ld a,c
    and %11110000
    jr z,_ez1
    inc d
    inc d
_ez1:
    inc d
    inc d
_nexthalf:
    and %10101010
    ret z
    ld c,a
    jp pe,_e2
    and %00001111
    jr z,_oz2
    jp pe,_oe2
    ld a,c
    and %11110000
    jr z,_oz2
    inc d
    ret
_oe2:
    inc d
    inc d
_oz2:
    inc d
    ret
_e2:
    and %00001111
    jr z,_ez2
    jp po,_ez2
    ld a,c
    and %11110000
    jr z,_ez2
    inc d
    inc d
_ez2:
    inc d
    inc d
    ret