match.asm

; 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>

	.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 ?
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