+++ /dev/null
-; 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.
-
- name match
-
-ifndef DYN_ALLOC
- extrn _prev : word
- extrn _window : byte
- prev equ _prev ; offset part
- window equ _window
-endif
-
-_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 : word
-ifdef 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 0
-else
- wseg dw seg _window
- window_seg equ wseg
- window_off equ offset _window
-endif
-_DATA ends
-
-DGROUP 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 array
-ifdef SS_NEQ_DS
- match_start dw 0 ; copy of _match_start if SS != DS
- nice_match dw 0 ; copy of _nice_match if SS != DS
-endif
-
-; initialize or check the variables used in match.asm.
-
-ifdef __LARGE__
-_match_init proc far ; 'proc far' for large model
-else
-_match_init proc near ; 'proc near' for compact model
-endif
-ifdef 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/2
-else
- 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 error
-endif
-ifdef 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
- endif
-else
- prev_seg equ cs:prev_ptr
-endif
- ret
-ifdef __LARGE__
- extrn _exit : far ; 'far' for large model
-else
- extrn _exit : near ; 'near' for compact model
-endif
-error: 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 model
-else
-_longest_match proc near ; 'proc near' for compact model
-endif
- push bp
- mov bp,sp
- push di
- push si
- push ds
-
-ifdef __LARGE__
- cur_match equ word ptr [bp+6] ; [bp+6] for large model
-else
- cur_match equ word ptr [bp+4] ; [bp+4] for compact model
-endif
-
-; 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 = NIL
-limit_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 branch
-long_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 array
-short_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=32768
-endif
- 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_end
-do_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_loop
-the_end:
- pop ds
- assume ds: DGROUP
-ifdef SS_NEQ_DS
- mov ax,ma_start ; garbage if no match found
- mov ds:_match_start,ax
-endif
- pop si
- pop di
- pop bp
- mov ax,bx ; result = ax = best_len
- ret
-maxmatch: ; come here if maximum match
- cmpsb ; increment si and di
- jmp mismatch ; force match_length = MAX_LENGTH
-
-_longest_match endp
-
-_TEXT ends
-end
projects / debian / gzip / blobdiff