AverageBGR565

; Calculates the average of the BGR565 (or RGB565) colors in DE and HL into HL.
;    I: DE=color1, HL=color2
;    O: A=color1&$FF&~((1<<5)+1), BC=color1&color2&(((1<<6)+1<<5)+1),
;       DE=color1&~(((1<<6)+1<<5)+1), HL=average(color1,color2)
;   FO: SZP(L), C=0
;   CC: 125
AverageBGR565:
    ld  a,d
    and h
    and 1<<(6+5-8)
    ld  b,a
    ld  a,e
    and l
    and (1<<5)+1
    ld  c,a
    res (6+5)&7,d
    ld  a,e
    and ~((1<<5)+1)
    ld  e,a
    res (6+5)&7,h
    res 5,l
    add hl,de
    rr  h
    rr  l
    add hl,bc
    ret