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