; match.asm -- Pentium-Pro optimized version of longest_match()

;

; Updated for zlib 1.1.3 and converted to MASM 6.1x

; Copyright (C) 2000 Dan Higdon <hdan@kinesoft.com>

;                    and Chuck Walbourn <chuckw@kinesoft.com>

; Corrections by Cosmin Truta <cosmint@cs.ubbcluj.ro>

;

; This is free software; you can redistribute it and/or modify it

; under the terms of the GNU General Public License.

; Based on match.S

; Written for zlib 1.1.2

; Copyright (C) 1998 Brian Raiter <breadbox@muppetlabs.com>

;

; Modified by Gilles Vollant (2005) for add gzhead and gzindex

	.686P

	.MODEL	FLAT

;===========================================================================

; EQUATES

;===========================================================================

MAX_MATCH	EQU 258

MIN_MATCH	EQU 3

MIN_LOOKAHEAD	EQU (MAX_MATCH + MIN_MATCH + 1)

MAX_MATCH_8	EQU ((MAX_MATCH + 7) AND (NOT 7))

;===========================================================================

; STRUCTURES

;===========================================================================

; This STRUCT assumes a 4-byte alignment

DEFLATE_STATE	STRUCT

ds_strm			dd ?

ds_status		dd ?

ds_pending_buf		dd ?

ds_pending_buf_size	dd ?

ds_pending_out		dd ?

ds_pending		dd ?

ds_wrap			dd ?

; gzhead and gzindex are added in zlib 1.2.2.2 (see deflate.h)

ds_gzhead               dd ?

ds_gzindex              dd ?

ds_data_type		db ?

ds_method		db ?

			db ?	; padding

			db ?	; padding

ds_last_flush		dd ?

ds_w_size		dd ?	; used

ds_w_bits		dd ?

ds_w_mask		dd ?	; used

ds_window		dd ?	; used

ds_window_size		dd ?

ds_prev			dd ?	; used

ds_head			dd ?

ds_ins_h		dd ?

ds_hash_size		dd ?

ds_hash_bits		dd ?

ds_hash_mask		dd ?

ds_hash_shift		dd ?

ds_block_start		dd ?

ds_match_length		dd ?	; used

ds_prev_match		dd ?	; used

ds_match_available	dd ?

ds_strstart		dd ?	; used

ds_match_start		dd ?	; used

ds_lookahead		dd ?	; used

ds_prev_length		dd ?	; used

ds_max_chain_length	dd ?	; used

ds_max_laxy_match	dd ?

ds_level		dd ?

ds_strategy		dd ?

ds_good_match		dd ?	; used

ds_nice_match		dd ?	; used

; Don't need anymore of the struct for match

DEFLATE_STATE	ENDS

;===========================================================================

; CODE

;===========================================================================

_TEXT	SEGMENT

;---------------------------------------------------------------------------

; match_init

;---------------------------------------------------------------------------

	ALIGN	4

PUBLIC	_match_init

_match_init	PROC

	; no initialization needed

	ret

_match_init	ENDP

;---------------------------------------------------------------------------

; uInt longest_match(deflate_state *deflatestate, IPos curmatch)

;---------------------------------------------------------------------------

	ALIGN	4

PUBLIC	_longest_match

_longest_match	PROC

; Since this code uses EBP for a scratch register, the stack frame must

; be manually constructed and referenced relative to the ESP register.

; Stack image

; Variables

chainlenwmask	=  0	; high word: current chain len

			; low word: s->wmask

window		=  4	; local copy of s->window

windowbestlen	=  8	; s->window + bestlen

scanend		= 12	; last two bytes of string

scanstart	= 16	; first two bytes of string

scanalign	= 20	; dword-misalignment of string

nicematch	= 24	; a good enough match size

bestlen		= 28	; size of best match so far

scan		= 32	; ptr to string wanting match

varsize		= 36	; number of bytes (also offset to last saved register)

; Saved Registers (actually pushed into place)

ebx_save	= 36

edi_save	= 40

esi_save	= 44

ebp_save	= 48

; Parameters

retaddr		= 52

deflatestate	= 56

curmatch	= 60

; Save registers that the compiler may be using

	push	ebp

	push	edi

	push	esi

	push	ebx

; Allocate local variable space

	sub	esp,varsize

; Retrieve the function arguments. ecx will hold cur_match

; throughout the entire function. edx will hold the pointer to the

; deflate_state structure during the function's setup (before

; entering the main loop).

	mov	edx, [esp+deflatestate]

ASSUME	edx:PTR DEFLATE_STATE

	mov	ecx, [esp+curmatch]

; uInt wmask = s->w_mask;

; unsigned chain_length = s->max_chain_length;

; if (s->prev_length >= s->good_match) {

;     chain_length >>= 2;

; }

	mov	eax, [edx].ds_prev_length

	mov	ebx, [edx].ds_good_match

	cmp	eax, ebx

	mov	eax, [edx].ds_w_mask

	mov	ebx, [edx].ds_max_chain_length

	jl	SHORT LastMatchGood

	shr	ebx, 2

LastMatchGood:

; chainlen is decremented once beforehand so that the function can

; use the sign flag instead of the zero flag for the exit test.

; It is then shifted into the high word, to make room for the wmask

; value, which it will always accompany.

	dec	ebx

	shl	ebx, 16

	or	ebx, eax

	mov	[esp+chainlenwmask], ebx

; if ((uInt)nice_match > s->lookahead) nice_match = s->lookahead;

	mov	eax, [edx].ds_nice_match

	mov	ebx, [edx].ds_lookahead

	cmp	ebx, eax

	jl	SHORT LookaheadLess

	mov	ebx, eax

LookaheadLess:

	mov	[esp+nicematch], ebx

;/* register Bytef *scan = s->window + s->strstart;                     */

	mov	esi, [edx].ds_window

	mov	[esp+window], esi

	mov	ebp, [edx].ds_strstart

	lea	edi, [esi+ebp]

	mov	[esp+scan],edi

;/* Determine how many bytes the scan ptr is off from being             */

;/* dword-aligned.                                                      */

	mov	eax, edi

	neg	eax

	and	eax, 3

	mov	[esp+scanalign], eax

;/* IPos limit = s->strstart > (IPos)MAX_DIST(s) ?                      */

;/*     s->strstart - (IPos)MAX_DIST(s) : NIL;                          */

	mov	eax, [edx].ds_w_size

	sub	eax, MIN_LOOKAHEAD

	sub	ebp, eax

	jg	SHORT LimitPositive

	xor	ebp, ebp

LimitPositive:

;/* int best_len = s->prev_length;                                      */

	mov	eax, [edx].ds_prev_length

	mov	[esp+bestlen], eax

;/* Store the sum of s->window + best_len in %esi locally, and in %esi. */

	add	esi, eax

	mov	[esp+windowbestlen], esi

;/* register ush scan_start = *(ushf*)scan;                             */

;/* register ush scan_end   = *(ushf*)(scan+best_len-1);                */

;/* Posf *prev = s->prev;                                               */

	movzx	ebx, WORD PTR[edi]

	mov	[esp+scanstart], ebx

	movzx	ebx, WORD PTR[eax+edi-1]

	mov	[esp+scanend], ebx

	mov	edi, [edx].ds_prev

;/* Jump into the main loop.                                            */

	mov	edx, [esp+chainlenwmask]

	jmp	SHORT LoopEntry

;/* do {

; *     match = s->window + cur_match;

; *     if (*(ushf*)(match+best_len-1) != scan_end ||

; *         *(ushf*)match != scan_start) continue;

; *     [...]

; * } while ((cur_match = prev[cur_match & wmask]) > limit

; *          && --chain_length != 0);

; *

; * Here is the inner loop of the function. The function will spend the

; * majority of its time in this loop, and majority of that time will

; * be spent in the first ten instructions.

; *

; * Within this loop:

; * %ebx = scanend

; * %ecx = curmatch

; * %edx = chainlenwmask - i.e., ((chainlen << 16) | wmask)

; * %esi = windowbestlen - i.e., (window + bestlen)

; * %edi = prev

; * %ebp = limit

; */

	ALIGN	4

LookupLoop:

	and	ecx, edx

	movzx	ecx, WORD PTR[edi+ecx*2]

	cmp	ecx, ebp

	jbe	LeaveNow

	sub	edx, 000010000H

	js	LeaveNow

LoopEntry:

	movzx	eax, WORD PTR[esi+ecx-1]

	cmp	eax, ebx

	jnz	SHORT LookupLoop

	mov	eax, [esp+window]

	movzx	eax, WORD PTR[eax+ecx]

	cmp	eax, [esp+scanstart]

	jnz	SHORT LookupLoop

;/* Store the current value of chainlen.                                */

	mov	[esp+chainlenwmask], edx

;/* Point %edi to the string under scrutiny, and %esi to the string we  */

;/* are hoping to match it up with. In actuality, %esi and %edi are     */

;/* both pointed (MAX_MATCH_8 - scanalign) bytes ahead, and %edx is     */

;/* initialized to -(MAX_MATCH_8 - scanalign).                          */

	mov	esi, [esp+window]

	mov	edi, [esp+scan]

	add	esi, ecx

	mov	eax, [esp+scanalign]

	mov	edx, -MAX_MATCH_8

	lea	edi, [edi+eax+MAX_MATCH_8]

	lea	esi, [esi+eax+MAX_MATCH_8]

;/* Test the strings for equality, 8 bytes at a time. At the end,

; * adjust %edx so that it is offset to the exact byte that mismatched.

; *

; * We already know at this point that the first three bytes of the

; * strings match each other, and they can be safely passed over before

; * starting the compare loop. So what this code does is skip over 0-3

; * bytes, as much as necessary in order to dword-align the %edi

; * pointer. (%esi will still be misaligned three times out of four.)

; *

; * It should be confessed that this loop usually does not represent

; * much of the total running time. Replacing it with a more

; * straightforward "rep cmpsb" would not drastically degrade

; * performance.

; */

LoopCmps:

	mov	eax, DWORD PTR[esi+edx]

	xor	eax, DWORD PTR[edi+edx]

	jnz	SHORT LeaveLoopCmps

	mov	eax, DWORD PTR[esi+edx+4]

	xor	eax, DWORD PTR[edi+edx+4]

	jnz	SHORT LeaveLoopCmps4

	add	edx, 8

	jnz	SHORT LoopCmps

	jmp	LenMaximum

	ALIGN	4

LeaveLoopCmps4:

	add	edx, 4

LeaveLoopCmps:

	test	eax, 00000FFFFH

	jnz	SHORT LenLower

	add	edx, 2

	shr	eax, 16

LenLower:

	sub	al, 1

	adc	edx, 0

;/* Calculate the length of the match. If it is longer than MAX_MATCH,  */

;/* then automatically accept it as the best possible match and leave.  */

	lea	eax, [edi+edx]

	mov	edi, [esp+scan]

	sub	eax, edi

	cmp	eax, MAX_MATCH

	jge	SHORT LenMaximum

;/* If the length of the match is not longer than the best match we     */

;/* have so far, then forget it and return to the lookup loop.          */

	mov	edx, [esp+deflatestate]

	mov	ebx, [esp+bestlen]

	cmp	eax, ebx

	jg	SHORT LongerMatch

	mov	esi, [esp+windowbestlen]

	mov	edi, [edx].ds_prev

	mov	ebx, [esp+scanend]

	mov	edx, [esp+chainlenwmask]

	jmp	LookupLoop

	ALIGN	4

;/*         s->match_start = cur_match;                                 */

;/*         best_len = len;                                             */

;/*         if (len >= nice_match) break;                               */

;/*         scan_end = *(ushf*)(scan+best_len-1);                       */

LongerMatch:

	mov	ebx, [esp+nicematch]

	mov	[esp+bestlen], eax

	mov	[edx].ds_match_start, ecx

	cmp	eax, ebx

	jge	SHORT LeaveNow

	mov	esi, [esp+window]

	add	esi, eax

	mov	[esp+windowbestlen], esi

	movzx	ebx, WORD PTR[edi+eax-1]

	mov	edi, [edx].ds_prev

	mov	[esp+scanend], ebx

	mov	edx, [esp+chainlenwmask]

	jmp	LookupLoop

	ALIGN	4

;/* Accept the current string, with the maximum possible length.        */

LenMaximum:

	mov	edx, [esp+deflatestate]

	mov	DWORD PTR[esp+bestlen], MAX_MATCH

	mov	[edx].ds_match_start, ecx

;/* if ((uInt)best_len <= s->lookahead) return (uInt)best_len;          */

;/* return s->lookahead;                                                */

LeaveNow:

	mov	edx, [esp+deflatestate]

	mov	ebx, [esp+bestlen]

	mov	eax, [edx].ds_lookahead

	cmp	ebx, eax

	jg	SHORT LookaheadRet

	mov	eax, ebx

LookaheadRet:

; Restore the stack and return from whence we came.

	add	esp, varsize

	pop	ebx

	pop	esi

	pop	edi

	pop	ebp

	ret

_longest_match	ENDP

_TEXT	ENDS

END