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match32.asm
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;===========================================================================
; Copyright (c) 1990-2005 Info-ZIP. All rights reserved.
;
; See the accompanying file LICENSE, version 2005-Feb-10 or later
; (the contents of which are also included in zip.h) for terms of use.
; If, for some reason, all these files are missing, the Info-ZIP license
; also may be found at: ftp://ftp.info-zip.org/pub/infozip/license.html
;===========================================================================
;
; 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 make sure this is
; assembled with an equivalent -DWSIZE=<whatever>.
; Caution: this module works for IBM's C/C++ compiler versions 2 and 3
; and for Watcom's 32-bit C/C++ compiler. Both pass the first (and only)
; argument for longest_match in the EAX register, not on the stack, with
; the default calling conventions (_System would use the stack).
;
;==============================================================================
;
; Do NOT assemble this source if external crc32 routine from zlib gets used.
;
IFNDEF USE_ZLIB
;
.386
name match
BSS32 segment dword USE32 public 'BSS'
extrn window : byte
extrn prev : word
extrn prev_length : dword
extrn strstart : dword
extrn match_start : dword
extrn max_chain_length : dword
extrn good_match : dword
extrn nice_match : dword
BSS32 ends
CODE32 segment dword USE32 public 'CODE'
assume cs:CODE32, ds:FLAT, ss:FLAT
public match_init
public longest_match
ifndef WSIZE
WSIZE equ 32768 ; keep in sync with zip.h !
endif
MIN_MATCH equ 3
MAX_MATCH equ 258
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
; return address ; esp+16
push ebp ; esp+12
push edi ; esp+8
push esi ; esp+4
lea ebx,window
add ebx,2
window_off equ dword ptr [esp]
push ebx ; esp
; match equ esi
; scan equ edi
; chain_length equ ebp
; best_len equ ebx
; limit equ edx
mov esi,eax ; cur_match
mov edx,strstart
mov ebp,max_chain_length ; chain_length = max_chain_length
mov edi,edx
sub edx,MAX_DIST ; limit = strstart-MAX_DIST
cld ; string ops increment esi and edi
jae short limit_ok
sub edx,edx ; limit = NIL
limit_ok:
add edi,window_off ; edi = offset(window + strstart + 2)
mov ebx,prev_length ; best_len = prev_length
mov cx,[edi-2] ; cx = scan[0..1]
mov ax,[ebx+edi-3] ; ax = scan[best_len-1..best_len]
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:
; 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 ; not needed if WSIZE=32768
dec ebp ; --chain_length
shl esi,1 ; cur_match as word index
mov si,prev[esi] ; cur_match = prev[cur_match]
; top word of esi is still 0
jz the_end
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
add esi,window_off ; esi = match
mov ecx,(MAX_MATCH-2)/2 ; scan for at most MAX_MATCH bytes
mov eax,edi ; eax = scan+2
repe cmpsw ; loop until mismatch
je maxmatch ; match of length MAX_MATCH?
mismatch:
mov cl,[edi-2] ; mismatch on first or second byte?
xchg eax,edi ; edi = scan+2, eax = end of scan
sub cl,[esi-2] ; cl = 0 if first bytes equal
sub eax,edi ; eax = len
sub esi,window_off ; esi = match - (2 + offset(window))
sub esi,eax ; esi = cur_match (= match - len)
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
ifdef FULL_SEARCH
cmp eax,MAX_MATCH ; len >= MAX_MATCH ?
else
cmp eax,nice_match ; len >= nice_match ?
endif
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
CODE32 ends
;
ENDIF ; !USE_ZLIB
;
end