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dzx1_mega.asm
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dzx1_mega.asm
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; -----------------------------------------------------------------------------
; ZX1 decoder by Einar Saukas & introspec
; "Mega" version (406 bytes, 25% faster)
; -----------------------------------------------------------------------------
; Parameters:
; HL: source address (compressed data)
; DE: destination address (decompressing)
; -----------------------------------------------------------------------------
dzx1_mega:
ld bc, $ffff ; preserve default offset 1
ld (dzx1m_last_offset+1), bc
inc bc
jr dzx1m_literals0
dzx1m_new_offset6:
dec b
ld c, (hl) ; obtain offset LSB
inc hl
rr c ; single byte offset?
jr nc, dzx1m_msb_skip6
ld b, (hl) ; obtain offset MSB
inc hl
rr b ; replace last LSB bit with last MSB bit
inc b
ret z ; check end marker
rl c
dzx1m_msb_skip6:
ld (dzx1m_last_offset+1), bc ; preserve new offset
ld bc, 1
add a, a ; obtain length
jp nc, dzx1m_length5
add a, a
rl c
add a, a
jr nc, dzx1m_length3
dzx1m_elias_length3:
add a, a
rl c
rl b
add a, a
jp c, dzx1m_elias_length1
dzx1m_length1:
inc bc
push hl ; preserve source
ld hl, (dzx1m_last_offset+1)
add hl, de ; calculate destination - offset
ldir ; copy from offset
pop hl ; restore source
add a, a ; copy from literals or new offset?
jr c, dzx1m_new_offset0
dzx1m_literals0:
inc c
ld a, (hl) ; load another group of 8 bits
inc hl
add a, a ; obtain length
jr nc, dzx1m_literals7
dzx1m_elias_literals7:
add a, a
rl c
rl b
add a, a
jp c, dzx1m_elias_literals5
dzx1m_literals5:
ldir ; copy literals
add a, a ; copy from last offset or new offset?
jp c, dzx1m_new_offset4
inc c
add a, a ; obtain length
jr nc, dzx1m_reuse3
dzx1m_elias_reuse3:
add a, a
rl c
rl b
add a, a
jp c, dzx1m_elias_reuse1
dzx1m_reuse1:
push hl ; preserve source
ld hl, (dzx1m_last_offset+1)
add hl, de ; calculate destination - offset
ldir ; copy from offset
pop hl ; restore source
add a, a ; copy from literals or new offset?
jr nc, dzx1m_literals0
dzx1m_new_offset0:
dec b
ld c, (hl) ; obtain offset LSB
inc hl
rr c ; single byte offset?
jr nc, dzx1m_msb_skip0
ld b, (hl) ; obtain offset MSB
inc hl
rr b ; replace last LSB bit with last MSB bit
inc b
ret z ; check end marker
rl c
dzx1m_msb_skip0:
ld (dzx1m_last_offset+1), bc ; preserve new offset
ld bc, 1
ld a, (hl) ; load another group of 8 bits
inc hl
add a, a ; obtain length
jp nc, dzx1m_length7
add a, a
rl c
add a, a
jr nc, dzx1m_length5
dzx1m_elias_length5:
add a, a
rl c
rl b
add a, a
jr c, dzx1m_elias_length3
dzx1m_length3:
inc bc
push hl ; preserve source
ld hl, (dzx1m_last_offset+1)
add hl, de ; calculate destination - offset
ldir ; copy from offset
pop hl ; restore source
add a, a ; copy from literals or new offset?
jr c, dzx1m_new_offset2
dzx1m_literals2:
inc c
add a, a ; obtain length
jr nc, dzx1m_literals1
dzx1m_elias_literals1:
add a, a
rl c
rl b
ld a, (hl) ; load another group of 8 bits
inc hl
add a, a
jr c, dzx1m_elias_literals7
dzx1m_literals7:
ldir ; copy literals
add a, a ; copy from last offset or new offset?
jp c, dzx1m_new_offset6
inc c
add a, a ; obtain length
jr nc, dzx1m_reuse5
dzx1m_elias_reuse5:
add a, a
rl c
rl b
add a, a
jr c, dzx1m_elias_reuse3
dzx1m_reuse3:
push hl ; preserve source
ld hl, (dzx1m_last_offset+1)
add hl, de ; calculate destination - offset
ldir ; copy from offset
pop hl ; restore source
add a, a ; copy from literals or new offset?
jr nc, dzx1m_literals2
dzx1m_new_offset2:
dec b
ld c, (hl) ; obtain offset LSB
inc hl
rr c ; single byte offset?
jr nc, dzx1m_msb_skip2
ld b, (hl) ; obtain offset MSB
inc hl
rr b ; replace last LSB bit with last MSB bit
inc b
ret z ; check end marker
rl c
dzx1m_msb_skip2:
ld (dzx1m_last_offset+1), bc ; preserve new offset
ld bc, 1
add a, a ; obtain length
jp nc, dzx1m_length1
add a, a
rl c
ld a, (hl) ; load another group of 8 bits
inc hl
add a, a
jr nc, dzx1m_length7
dzx1m_elias_length7:
add a, a
rl c
rl b
add a, a
jr c, dzx1m_elias_length5
dzx1m_length5:
inc bc
push hl ; preserve source
ld hl, (dzx1m_last_offset+1)
add hl, de ; calculate destination - offset
ldir ; copy from offset
pop hl ; restore source
add a, a ; copy from literals or new offset?
jr c, dzx1m_new_offset4
dzx1m_literals4:
inc c
add a, a ; obtain length
jr nc, dzx1m_literals3
dzx1m_elias_literals3:
add a, a
rl c
rl b
add a, a
jr c, dzx1m_elias_literals1
dzx1m_literals1:
ldir ; copy literals
add a, a ; copy from last offset or new offset?
jp c, dzx1m_new_offset0
inc c
ld a, (hl) ; load another group of 8 bits
inc hl
add a, a ; obtain length
jr nc, dzx1m_reuse7
dzx1m_elias_reuse7:
add a, a
rl c
rl b
add a, a
jr c, dzx1m_elias_reuse5
dzx1m_reuse5:
push hl ; preserve source
ld hl, (dzx1m_last_offset+1)
add hl, de ; calculate destination - offset
ldir ; copy from offset
pop hl ; restore source
add a, a ; copy from literals or new offset?
jr nc, dzx1m_literals4
dzx1m_new_offset4:
dec b
ld c, (hl) ; obtain offset LSB
inc hl
rr c ; single byte offset?
jr nc, dzx1m_msb_skip4
ld b, (hl) ; obtain offset MSB
inc hl
rr b ; replace last LSB bit with last MSB bit
inc b
ret z ; check end marker
rl c
dzx1m_msb_skip4:
ld (dzx1m_last_offset+1), bc ; preserve new offset
ld bc, 1
add a, a ; obtain length
jp nc, dzx1m_length3
add a, a
rl c
add a, a
jp nc, dzx1m_length1
dzx1m_elias_length1:
add a, a
rl c
rl b
ld a, (hl) ; load another group of 8 bits
inc hl
add a, a
jr c, dzx1m_elias_length7
dzx1m_length7:
inc bc
push hl ; preserve source
ld hl, (dzx1m_last_offset+1)
add hl, de ; calculate destination - offset
ldir ; copy from offset
pop hl ; restore source
add a, a ; copy from literals or new offset?
jp c, dzx1m_new_offset6
dzx1m_literals6:
inc c
add a, a ; obtain length
jp nc, dzx1m_literals5
dzx1m_elias_literals5:
add a, a
rl c
rl b
add a, a
jr c, dzx1m_elias_literals3
dzx1m_literals3:
ldir ; copy literals
add a, a ; copy from last offset or new offset?
jp c, dzx1m_new_offset2
inc c
add a, a ; obtain length
jp nc, dzx1m_reuse1
dzx1m_elias_reuse1:
add a, a
rl c
rl b
ld a, (hl) ; load another group of 8 bits
inc hl
add a, a
jr c, dzx1m_elias_reuse7
dzx1m_reuse7:
push hl ; preserve source
dzx1m_last_offset:
ld hl, 0
add hl, de ; calculate destination - offset
ldir ; copy from offset
pop hl ; restore source
add a, a ; copy from literals or new offset?
jr nc, dzx1m_literals6
jp dzx1m_new_offset6
; -----------------------------------------------------------------------------