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|
FlagActionPredef: ; f4ec (3:74ec)
call GetPredefRegisters
FlagAction: ; f4ef (3:74ef)
; Perform action b on bit c
; in the bitfield at hl.
; 0: reset
; 1: set
; 2: read
; Return the result in c.
push hl
push de
push bc
; bit
ld a, c
ld d, a
and 7
ld e, a
; byte
ld a, d
srl a
srl a
srl a
add l
ld l, a
jr nc, .ok
inc h
.ok
; d = 1 << e (bitmask)
inc e
ld d, 1
.shift
dec e
jr z, .shifted
sla d
jr .shift
.shifted
ld a, b
and a
jr z, .reset
cp 2
jr z, .read
.set
ld b, [hl]
ld a, d
or b
ld [hl], a
jr .done
.reset
ld b, [hl]
ld a, d
xor $ff
and b
ld [hl], a
jr .done
.read
ld b, [hl]
ld a, d
and b
.done
pop bc
pop de
pop hl
ld c, a
ret
|
