Hi!
Don't know if reinventing the wheel but...
; Overwrites [hl] with a, but only the bits specified by b.
; i.e.: [hl] = a = ([hl] & not(b)) | (a & b)
; param hl: destination address
; param a: value to set
; param b: mask
; return a: value set
LD_HL_A_WITH_MASK:
xor [hl]
and b
xor [hl] ; ...15 tstates, 3 bytes
ld [hl], a ; ...23 tstates, 4 bytes (remove if not needed)
ret ; ...34 tstates, 5 bytes
If the mask is and known at compile time,
and b can be replaced by
and $nn.
And, of course, the original value can be accesed through [ix+n] or [iy+n] instead of [hl]. Or be in a register (c, d, e) instead of RAM.
