Skip to content

optimized zx7 #767

New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

Sign up for GitHub

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

Open
ZERICO2005 wants to merge 1 commit into
base: master
Choose a base branch
from
Open

optimized zx7 #767

Changes from all commits
Commits
Show all changes
1 commit
Select commit
File filter

Filter by extension

Filter by extension
Conversations
Failed to load comments.
Loading
Jump to
Jump to file
Failed to load files.
Loading
Diff view
Diff view
69 changes: 52 additions & 17 deletions src/ce/zx7.src
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -22,52 +22,87 @@ dzx7t_copy_byte_loop:
ldi ; copy literal byte
dzx7t_main_loop:
add a, a ; check next bit
call z, dzx7t_load_bits ; no more bits left?
jr nz, dzx7t_copy_byte_has_bits
; dzx7t_load_bits
ld a, (hl)
inc hl
rla
dzx7t_copy_byte_has_bits:
jr nc, dzx7t_copy_byte_loop ; next bit indicates either literal or sequence

; determine number of bits used for length (Elias gamma coding)

push de
ld de, 0
ld de, $FF00
ld bc, 1
dzx7t_len_size_loop:
inc d
add a, a ; check next bit
call z, dzx7t_load_bits ; no more bits left?
jr nz, dzx7t_len_size_has_bits
; dzx7t_load_bits
ld a, (hl)
inc hl
rla
dzx7t_len_size_has_bits:
inc d
jr nc, dzx7t_len_size_loop
jr dzx7t_len_value_start
jr z, dzx7t_len_value_start

; determine length

dzx7t_len_value_loop:
add a, a ; check next bit
call z, dzx7t_load_bits ; no more bits left?
jr nz, dzx7t_len_value_has_bits
; dzx7t_load_bits
ld a, (hl)
inc hl
rla
dzx7t_len_value_has_bits:
rl c
rl b
jr c, dzx7t_exit ; check end marker
dzx7t_len_value_start:
dec d
jr nz, dzx7t_len_value_loop
scf
dzx7t_len_value_start:
inc bc ; adjust length

; determine offset

ld e, (hl) ; load offset flag (1 bit) + offset value (7 bits)
inc hl
sla e
inc e
rl e ; sll e since carry is set
jr nc, dzx7t_offset_end ; if offset flag is set, load 4 extra bits
add a, a ; check next bit
call z, dzx7t_load_bits ; no more bits left?
jr nz, dzx7t_has_bits_1
; dzx7t_load_bits
ld a, (hl)
inc hl
rla
dzx7t_has_bits_1:
rl d ; insert first bit into D
add a, a ; check next bit
call z, dzx7t_load_bits ; no more bits left?
jr nz, dzx7t_has_bits_2
; dzx7t_load_bits
ld a, (hl)
inc hl
rla
dzx7t_has_bits_2:
rl d ; insert second bit into D
add a, a ; check next bit
call z, dzx7t_load_bits ; no more bits left?
jr nz, dzx7t_has_bits_3
; dzx7t_load_bits
ld a, (hl)
inc hl
rla
dzx7t_has_bits_3:
rl d ; insert third bit into D
add a, a ; check next bit
call z, dzx7t_load_bits ; no more bits left?
jr nz, dzx7t_has_bits_4
; dzx7t_load_bits
ld a, (hl)
inc hl
rla
dzx7t_has_bits_4:
ccf
jr c, dzx7t_offset_end
inc d ; equivalent to adding 128 to DE
Expand All @@ -85,8 +120,8 @@ dzx7t_exit:
pop hl ; restore source address (compressed data)
jr nc, dzx7t_main_loop

dzx7t_load_bits:
ld a, (hl) ; load another group of 8 bits
inc hl
rla
; dzx7t_load_bits:
; ld a, (hl) ; load another group of 8 bits
; inc hl
; rla
ret
Loading