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match32.asm
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Assembly Source File
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1994-02-20
|
6KB
|
151 lines
;
; Copyright (C) 1990-1992 Mark Adler, Richard B. Wales, Jean-loup Gailly,
; Kai Uwe Rommel and Igor Mandrichenko.
; Permission is granted to any individual or institution to use, copy, or
; redistribute this software so long as all of the original files are included
; unmodified, that it is not sold for profit, and that this copyright notice
; is retained.
;
; match32.asm by Jean-loup Gailly.
; match32.asm, optimized version of longest_match() in deflate.c
; To be used only with 32 bit flat model. To simplify the code, the option
; -DDYN_ALLOC is not supported.
; This file is only optional. If you don't have an assembler, use the
; C version (add -DNO_ASM to CFLAGS in makefile and remove match.o
; from OBJI). If you have reduced WSIZE in zip.h, then change its value
; below.
; *** Warning: this file is still untested ***
.386
name match
_BSS segment dword USE32 public 'BSS'
extrn _match_start : dword
extrn _prev_length : dword
extrn _good_match : dword
extrn _strstart : dword
extrn _max_chain_length : dword
extrn _prev : word
extrn _window : byte
_BSS ends
DGROUP group _BSS
_TEXT segment dword USE32 public 'CODE'
assume cs: _TEXT, ds: DGROUP, ss: 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)
; initialize or check the variables used in match.asm.
match_init_ proc near
ret
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)
longest_match_ proc near
cur_match equ dword ptr [esp+20]
; return address ; esp+16
push ebp ; esp+12
push edi ; esp+8
push esi ; esp+4
push ebx ; esp
; match equ esi
; scan equ edi
; chain_length equ ebp
; best_len equ ebx
; limit equ edx
mov esi,cur_match
mov ebp,_max_chain_length ; chain_length = max_chain_length
mov edi,_strstart
mov edx,edi
sub edx,MAX_DIST ; limit = strstart-MAX_DIST
jae short limit_ok
sub edx,edx ; limit = NIL
limit_ok:
add edi,2+offset _window ; edi = offset(window + strstart + 2)
mov ebx,_prev_length ; best_len = prev_length
mov ax,[ebx+edi-3] ; ax = scan[best_len-1..best_len]
mov cx,[edi-2] ; cx = scan[0..1]
cmp ebx,_good_match ; do we have a good match already?
jb do_scan
shr ebp,2 ; chain_length >>= 2
jmp short do_scan
align 4 ; align destination of branch
long_loop:
; at this point, edi == scan+2, esi == cur_match
mov ax,[ebx+edi-3] ; ax = scan[best_len-1..best_len]
mov cx,[edi-2] ; cx = scan[0..1]
short_loop:
dec ebp ; --chain_length
jz the_end
; at this point, edi == scan+2, esi == cur_match,
; ax = scan[best_len-1..best_len] and cx = scan[0..1]
and esi,WSIZE-1
mov si,_prev[esi+esi] ; cur_match = prev[cur_match]
; top word of esi is still 0
cmp esi,edx ; cur_match <= limit ?
jbe short the_end
do_scan:
cmp ax,word ptr _window[ebx+esi-1] ; check match at best_len-1
jne short_loop
cmp cx,word ptr _window[esi] ; check min_match_length match
jne short_loop
lea esi,_window[esi+2] ; si = match
mov eax,edi ; ax = scan+2
mov ecx,(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,[edi-2] ; mismatch on first or second byte?
sub cl,[esi-2] ; cl = 0 if first bytes equal
xchg eax,edi ; edi = scan+2, eax = end of scan
sub eax,edi ; eax = len
sub esi,eax ; esi = cur_match + 2 + offset(window)
sub esi,2+offset _window ; esi = cur_match
sub cl,1 ; set carry if cl == 0 (can't use DEC)
adc eax,0 ; eax = carry ? len+1 : len
cmp eax,ebx ; len > best_len ?
jle long_loop
mov _match_start,esi ; match_start = cur_match
mov ebx,eax ; ebx = best_len = len
cmp eax,MAX_MATCH ; len >= MAX_MATCH ?
jl long_loop
the_end:
mov eax,ebx ; result = eax = best_len
pop ebx
pop esi
pop edi
pop ebp
ret
maxmatch: ; come here if maximum match
cmpsb ; increment esi and edi
jmp mismatch ; force match_length = MAX_LENGTH
longest_match_ endp
_TEXT ends
end