; match.asm -- optional optimized asm version of longest match in deflate.c; Copyright (C) 1992-1993 Jean-loup Gailly; This is free software; you can redistribute it and/or modify it under the; terms of the GNU General Public License, see the file COPYING.;; Must be assembled with masm -ml. To be used only with C compact model; or large model. (For large model, assemble with -D__LARGE__).; This file is only optional. If you don't have masm or tasm, use the; C version (add -DNO_ASM to CFLAGS in makefile.msc and remove match.obj; from OBJI). If you have reduced WSIZE in zip.h, then change its value; below.;; Turbo C 2.0 does not support static allocation of more than 64K bytes per; file, and does not have SS == DS. So TC and BC++ users must use:;   tasm -ml -DDYN_ALLOC -DSS_NEQ_DS match;;; To simplify the code, the option -DDYN_ALLOC is supported for OS/2; only if the arrays are guaranteed to have zero offset (allocated by; halloc). We also require SS==DS. This is satisfied for MSC but not Turbo C.; $Id: match.asm,v 0.6 1993/01/21 18:49:05 jloup Exp $        name    matchifndef DYN_ALLOC        extrn   _prev         : word        extrn   _window       : byte        prev    equ  _prev    ; offset part        window  equ  _windowendif_DATA    segment  word public 'DATA'        extrn   _nice_match   : word        extrn   _match_start  : word        extrn   _prev_length  : word        extrn   _good_match   : word        extrn   _strstart     : word        extrn   _max_chain_length : wordifdef DYN_ALLOC        extrn   _prev         : word        extrn   _window       : word        prev    equ 0         ; offset forced to zero        window  equ 0        window_seg equ _window[2]	window_off equ 0else	wseg    dw seg _window        window_seg equ wseg	window_off equ offset _windowendif_DATA    endsDGROUP  group _DATA_TEXT   segment word public 'CODE'        assume  cs: _TEXT, ds: DGROUP	public _match_init        public _longest_match	MIN_MATCH     equ 3        MAX_MATCH     equ 258	WSIZE         equ 32768		; keep in sync with zip.h !	MIN_LOOKAHEAD equ (MAX_MATCH+MIN_MATCH+1)	MAX_DIST      equ (WSIZE-MIN_LOOKAHEAD)prev_ptr    dw  seg _prev		; pointer to the prev arrayifdef SS_NEQ_DS    match_start dw  0			; copy of _match_start if SS != DS    nice_match  dw  0			; copy of _nice_match  if SS != DSendif; initialize or check the variables used in match.asm.ifdef __LARGE___match_init proc far			; 'proc far' for large modelelse_match_init proc near			; 'proc near' for compact modelendififdef SS_NEQ_DS        ma_start equ cs:match_start	; does not work on OS/2        nice     equ cs:nice_match	mov	ax,_nice_match	mov     cs:nice_match,ax       	; ugly write to code, crash on OS/2else	assume ss: DGROUP        ma_start equ ss:_match_start        nice     equ ss:_nice_match        mov     ax,ds        mov     bx,ss        cmp     ax,bx                   ; SS == DS?        jne     errorendififdef DYN_ALLOC	cmp	_prev[0],0		; verify zero offset	jne	error	cmp	_window[0],0	jne	error  ifdef SS_NEQ_DS	mov	ax,_prev[2]		; segment value	mov     cs:prev_ptr,ax		; ugly write to code, crash on OS/2        prev_seg  equ cs:prev_ptr  else        prev_seg  equ ss:_prev[2]	; works on OS/2 if SS == DS  endifelse        prev_seg  equ cs:prev_ptrendif	retifdef __LARGE__	extrn   _exit : far		; 'far' for large modelelse	extrn   _exit : near		; 'near' for compact modelendiferror:  call    _exit_match_init endp; -----------------------------------------------------------------------; Set match_start to the longest match starting at the given string and; return its length. Matches shorter or equal to prev_length are discarded,; in which case the result is equal to prev_length and match_start is; garbage.; IN assertions: cur_match is the head of the hash chain for the current;   string (strstart) and its distance is <= MAX_DIST, and prev_length >= 1; int longest_match(cur_match)ifdef __LARGE___longest_match  proc far		 ; 'proc far' for large modelelse_longest_match  proc near		 ; 'proc near' for compact modelendif        push    bp        mov     bp,sp        push    di	push	si	push	dsifdef __LARGE__        cur_match    equ word ptr [bp+6] ; [bp+6] for large modelelse        cur_match    equ word ptr [bp+4] ; [bp+4] for compact modelendif;       window	     equ es:window (es:0 for DYN_ALLOC);       prev	     equ ds:prev;       match        equ es:si;       scan         equ es:di;       chain_length equ bp;       best_len     equ bx;       limit        equ dx	mov	si,cur_match            ; use bp before it is destroyed        mov     bp,_max_chain_length    ; chain_length = max_chain_length	mov	di,_strstart	mov	dx,di	sub	dx,MAX_DIST             ; limit = strstart-MAX_DIST	jae	limit_ok	sub	dx,dx			; limit = NILlimit_ok:        add     di,2+window_off         ; di = offset(window + strstart + 2)        mov     bx,_prev_length         ; best_len = prev_length	mov     es,window_seg        mov     ax,es:[bx+di-3]         ; ax = scan[best_len-1..best_len]        mov     cx,es:[di-2]            ; cx = scan[0..1]	cmp	bx,_good_match		; do we have a good match already?        mov     ds,prev_seg    		; (does not destroy the flags)        assume  ds: nothing        jb      do_scan			; good match?	shr	bp,1			; chain_length >>= 2	shr	bp,1        jmp     short do_scan        even                            ; align destination of branchlong_loop:; at this point, ds:di == scan+2, ds:si == cur_match        mov     ax,[bx+di-3]            ; ax = scan[best_len-1..best_len]        mov     cx,[di-2]               ; cx = scan[0..1]        mov     ds,prev_seg    		; reset ds to address the prev arrayshort_loop:; at this point, di == scan+2, si = cur_match,; ax = scan[best_len-1..best_len] and cx = scan[0..1]if (WSIZE-32768)        and     si,WSIZE-1              ; not needed if WSIZE=32768endif        shl     si,1                    ; cur_match as word index        mov     si,prev[si]             ; cur_match = prev[cur_match]        cmp     si,dx			; cur_match <= limit ?        jbe     the_end        dec     bp                      ; --chain_length        jz      the_enddo_scan:        cmp     ax,word ptr es:window[bx+si-1] ; check match at best_len-1        jne     short_loop        cmp     cx,word ptr es:window[si]      ; check min_match_length match        jne     short_loop        lea     si,window[si+2]         ; si = match        mov     ax,di                   ; ax = scan+2        mov     cx,es        mov     ds,cx			; ds = es = window        mov     cx,(MAX_MATCH-2)/2      ; scan for at most MAX_MATCH bytes        repe    cmpsw                   ; loop until mismatch        je      maxmatch                ; match of length MAX_MATCH?mismatch:        mov     cl,[di-2]               ; mismatch on first or second byte?        sub     cl,[si-2]               ; cl = 0 if first bytes equal        xchg    ax,di                   ; di = scan+2, ax = end of scan        sub     ax,di                   ; ax = len	sub	si,ax			; si = cur_match + 2 + offset(window)	sub	si,2+window_off         ; si = cur_match        sub     cl,1                    ; set carry if cl == 0 (can't use DEC)        adc     ax,0                    ; ax = carry ? len+1 : len        cmp     ax,bx                   ; len > best_len ?        jle     long_loop        mov     ma_start,si             ; match_start = cur_match        mov     bx,ax                   ; bx = best_len = len        cmp     ax,nice                 ; len >= nice_match ?        jl      long_loopthe_end:	pop	ds        assume  ds: DGROUPifdef SS_NEQ_DS	mov	ax,ma_start		; garbage if no match found	mov	ds:_match_start,axendif        pop     si        pop     di        pop     bp        mov     ax,bx                   ; result = ax = best_len        retmaxmatch:                               ; come here if maximum match        cmpsb                           ; increment si and di        jmp     mismatch                ; force match_length = MAX_LENGTH        _longest_match  endp_TEXT   endsend