OPT proposal about unzip-cpm-z80

[zx70]

I'd also suggest to use HL' for bleft and bitbuf

[zx70]

I created a pull request with those code parts I was able to test.
Using EXX seems more tricky than expected and probably should stay as an option (we never know whether the BIOS is leaving the alternate registers untouched).

[agn453]

; push de

; ld de,-4
; add iy,de
; pop de

dec iy
dec iy
dec iy
dec iy

; push de

; ld de,4
; add iy,de
; pop de

inc iy
inc iy
inc iy
inc iy

...why it was preferred the addition ? For the flags?

If you wish to optimise for size, the current method of PUSH, LD DE, ADD IY, POP uses 7 bytes versus 8 bytes for the INC IY or DEC IY solution. Squeezing every byte from the code was the goal at the time. In other places such as within loops, the code is optimised for speed.

[zx70]

Well, thinking at ways to save memory we could, in example put redundant code parts in a subroutine, like:

open_wr:
ld de,opbuf
ld c,setdma
call bdos
call setout
ld de,opfcb
ld c,fwrite
call bdos
ret

Another possible approach is to remove (or keep optional) those compression methods which are not used anymore.

[agn453]

I've merged your #12 changes and bumped the CP/M UNZIP version to v1.5-7. Thanks.

[zx70]

This one is a little bit extreme, but in my test case reduces the timing count (z88dk-ticks) from 28210377 to 26158350.
It can be extended to the whole "getbits" logic and probably helps in saving a little more if correctly implemented.
The only problem is that we must trust the BIOS (and BDOS) not be touching the alternate registers set, which should be the case if it is well written. Otherwise we should preserve HL' before using the BDOS calls.

    ;
    nextsymbol:
        ld	(treep),hl
    
        exx
        ld	hl,(bitbuf)	; keep bitbuf in L, bleft in H
        exx
    
    nsloop:
    ;	push	hl
        exx
        ;ld	hl,(bitbuf)	; keep bitbuf in L, bleft in H
        dec	h
        jp	p,$+9		; jump to "xor a", past jp op plus 6 bytes:
        call	getbyte		; (3 bytes)
        ld	l,a		; (1 byte)  new bitbuf
        ld	h,7		; (2 bytes) 8 bits left, pre-dec'd
        xor	a		; jp op above jumps here
        rr	l
    ;	ld	(bitbuf),hl	; update bitbuf/bleft
        exx
        ;ld	h,a		; A still zero
        rla			; return bit in HL and A
        ;ld	l,a

    ;	pop	hl
        or	a
        jr	z,nsleft
        inc	hl
        inc	hl
    nsleft:
        ld	e,(hl)
        inc	hl
        ld	d,(hl)
    
        ld	a,d
        cp	10h
        jr	nc,nsleaf
        or	e
        ;ret	z
        jr	z,nsexit
    
        ld	hl,(treep)
        add	hl,de
        add	hl,de
        add	hl,de
        add	hl,de
        jr	nsloop
    
    nsleaf:	and	0fh
        ld	d,a
    nsexit:
    
        exx
        ld	(bitbuf),hl	; keep bitbuf in L, bleft in H
        exx
        ret

[zx70]

One step further...

    ;	rd1bit
    ;	push	af
    ;
    ;	ld	a,2
    ;	call	rdbybits
    ;	or	a
    
        ld	a,3		; better to gather 3 bits at once, it's faster and smaller
        call	rdbybits
        
        ld l,a
        and 1		; keep the first bit
        push af
    
        ld	a,l		; now onto the next 2 bits
        srl	a