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      1 /* match.S -- x86 assembly version of the zlib longest_match() function.
      2  * Optimized for the Intel 686 chips (PPro and later).
      3  *
      4  * Copyright (C) 1998, 2007 Brian Raiter <breadbox (at) muppetlabs.com>
      5  *
      6  * This software is provided 'as-is', without any express or implied
      7  * warranty.  In no event will the author be held liable for any damages
      8  * arising from the use of this software.
      9  *
     10  * Permission is granted to anyone to use this software for any purpose,
     11  * including commercial applications, and to alter it and redistribute it
     12  * freely, subject to the following restrictions:
     13  *
     14  * 1. The origin of this software must not be misrepresented; you must not
     15  *    claim that you wrote the original software. If you use this software
     16  *    in a product, an acknowledgment in the product documentation would be
     17  *    appreciated but is not required.
     18  * 2. Altered source versions must be plainly marked as such, and must not be
     19  *    misrepresented as being the original software.
     20  * 3. This notice may not be removed or altered from any source distribution.
     21  */
     22 
     23 #ifndef NO_UNDERLINE
     24 #define	match_init	_match_init
     25 #define	longest_match	_longest_match
     26 #endif
     27 
     28 #define	MAX_MATCH	(258)
     29 #define	MIN_MATCH	(3)
     30 #define	MIN_LOOKAHEAD	(MAX_MATCH + MIN_MATCH + 1)
     31 #define	MAX_MATCH_8	((MAX_MATCH + 7) & ~7)
     32 
     33 /* stack frame offsets */
     34 
     35 #define	chainlenwmask		0	/* high word: current chain len	*/
     36 					/* low word: s->wmask		*/
     37 #define	window			4	/* local copy of s->window	*/
     38 #define	windowbestlen		8	/* s->window + bestlen		*/
     39 #define	scanstart		16	/* first two bytes of string	*/
     40 #define	scanend			12	/* last two bytes of string	*/
     41 #define	scanalign		20	/* dword-misalignment of string	*/
     42 #define	nicematch		24	/* a good enough match size	*/
     43 #define	bestlen			28	/* size of best match so far	*/
     44 #define	scan			32	/* ptr to string wanting match	*/
     45 
     46 #define	LocalVarsSize		(36)
     47 /*	saved ebx		36 */
     48 /*	saved edi		40 */
     49 /*	saved esi		44 */
     50 /*	saved ebp		48 */
     51 /*	return address		52 */
     52 #define	deflatestate		56	/* the function arguments	*/
     53 #define	curmatch		60
     54 
     55 /* All the +zlib1222add offsets are due to the addition of fields
     56  *  in zlib in the deflate_state structure since the asm code was first written
     57  * (if you compile with zlib 1.0.4 or older, use "zlib1222add equ (-4)").
     58  * (if you compile with zlib between 1.0.5 and 1.2.2.1, use "zlib1222add equ 0").
     59  * if you compile with zlib 1.2.2.2 or later , use "zlib1222add equ 8").
     60  */
     61 
     62 #define zlib1222add		(8)
     63 
     64 #define	dsWSize			(36+zlib1222add)
     65 #define	dsWMask			(44+zlib1222add)
     66 #define	dsWindow		(48+zlib1222add)
     67 #define	dsPrev			(56+zlib1222add)
     68 #define	dsMatchLen		(88+zlib1222add)
     69 #define	dsPrevMatch		(92+zlib1222add)
     70 #define	dsStrStart		(100+zlib1222add)
     71 #define	dsMatchStart		(104+zlib1222add)
     72 #define	dsLookahead		(108+zlib1222add)
     73 #define	dsPrevLen		(112+zlib1222add)
     74 #define	dsMaxChainLen		(116+zlib1222add)
     75 #define	dsGoodMatch		(132+zlib1222add)
     76 #define	dsNiceMatch		(136+zlib1222add)
     77 
     78 
     79 .file "match.S"
     80 
     81 .globl	match_init, longest_match
     82 
     83 .text
     84 
     85 /* uInt longest_match(deflate_state *deflatestate, IPos curmatch) */
     86 .cfi_sections	.debug_frame
     87 
     88 longest_match:
     89 
     90 .cfi_startproc
     91 /* Save registers that the compiler may be using, and adjust %esp to	*/
     92 /* make room for our stack frame.					*/
     93 
     94 		pushl	%ebp
     95 		.cfi_def_cfa_offset 8
     96 		.cfi_offset ebp, -8
     97 		pushl	%edi
     98 		.cfi_def_cfa_offset 12
     99 		pushl	%esi
    100 		.cfi_def_cfa_offset 16
    101 		pushl	%ebx
    102 		.cfi_def_cfa_offset 20
    103 		subl	$LocalVarsSize, %esp
    104 		.cfi_def_cfa_offset LocalVarsSize+20
    105 
    106 /* Retrieve the function arguments. %ecx will hold cur_match		*/
    107 /* throughout the entire function. %edx will hold the pointer to the	*/
    108 /* deflate_state structure during the function's setup (before		*/
    109 /* entering the main loop).						*/
    110 
    111 		movl	deflatestate(%esp), %edx
    112 		movl	curmatch(%esp), %ecx
    113 
    114 /* uInt wmask = s->w_mask;						*/
    115 /* unsigned chain_length = s->max_chain_length;				*/
    116 /* if (s->prev_length >= s->good_match) {				*/
    117 /*     chain_length >>= 2;						*/
    118 /* }									*/
    119 
    120 		movl	dsPrevLen(%edx), %eax
    121 		movl	dsGoodMatch(%edx), %ebx
    122 		cmpl	%ebx, %eax
    123 		movl	dsWMask(%edx), %eax
    124 		movl	dsMaxChainLen(%edx), %ebx
    125 		jl	LastMatchGood
    126 		shrl	$2, %ebx
    127 LastMatchGood:
    128 
    129 /* chainlen is decremented once beforehand so that the function can	*/
    130 /* use the sign flag instead of the zero flag for the exit test.	*/
    131 /* It is then shifted into the high word, to make room for the wmask	*/
    132 /* value, which it will always accompany.				*/
    133 
    134 		decl	%ebx
    135 		shll	$16, %ebx
    136 		orl	%eax, %ebx
    137 		movl	%ebx, chainlenwmask(%esp)
    138 
    139 /* if ((uInt)nice_match > s->lookahead) nice_match = s->lookahead;	*/
    140 
    141 		movl	dsNiceMatch(%edx), %eax
    142 		movl	dsLookahead(%edx), %ebx
    143 		cmpl	%eax, %ebx
    144 		jl	LookaheadLess
    145 		movl	%eax, %ebx
    146 LookaheadLess:	movl	%ebx, nicematch(%esp)
    147 
    148 /* register Bytef *scan = s->window + s->strstart;			*/
    149 
    150 		movl	dsWindow(%edx), %esi
    151 		movl	%esi, window(%esp)
    152 		movl	dsStrStart(%edx), %ebp
    153 		lea	(%esi,%ebp), %edi
    154 		movl	%edi, scan(%esp)
    155 
    156 /* Determine how many bytes the scan ptr is off from being		*/
    157 /* dword-aligned.							*/
    158 
    159 		movl	%edi, %eax
    160 		negl	%eax
    161 		andl	$3, %eax
    162 		movl	%eax, scanalign(%esp)
    163 
    164 /* IPos limit = s->strstart > (IPos)MAX_DIST(s) ?			*/
    165 /*     s->strstart - (IPos)MAX_DIST(s) : NIL;				*/
    166 
    167 		movl	dsWSize(%edx), %eax
    168 		subl	$MIN_LOOKAHEAD, %eax
    169 		subl	%eax, %ebp
    170 		jg	LimitPositive
    171 		xorl	%ebp, %ebp
    172 LimitPositive:
    173 
    174 /* int best_len = s->prev_length;					*/
    175 
    176 		movl	dsPrevLen(%edx), %eax
    177 		movl	%eax, bestlen(%esp)
    178 
    179 /* Store the sum of s->window + best_len in %esi locally, and in %esi.	*/
    180 
    181 		addl	%eax, %esi
    182 		movl	%esi, windowbestlen(%esp)
    183 
    184 /* register ush scan_start = *(ushf*)scan;				*/
    185 /* register ush scan_end   = *(ushf*)(scan+best_len-1);			*/
    186 /* Posf *prev = s->prev;						*/
    187 
    188 		movzwl	(%edi), %ebx
    189 		movl	%ebx, scanstart(%esp)
    190 		movzwl	-1(%edi,%eax), %ebx
    191 		movl	%ebx, scanend(%esp)
    192 		movl	dsPrev(%edx), %edi
    193 
    194 /* Jump into the main loop.						*/
    195 
    196 		movl	chainlenwmask(%esp), %edx
    197 		jmp	LoopEntry
    198 
    199 .balign 16
    200 
    201 /* do {
    202  *     match = s->window + cur_match;
    203  *     if (*(ushf*)(match+best_len-1) != scan_end ||
    204  *         *(ushf*)match != scan_start) continue;
    205  *     [...]
    206  * } while ((cur_match = prev[cur_match & wmask]) > limit
    207  *          && --chain_length != 0);
    208  *
    209  * Here is the inner loop of the function. The function will spend the
    210  * majority of its time in this loop, and majority of that time will
    211  * be spent in the first ten instructions.
    212  *
    213  * Within this loop:
    214  * %ebx = scanend
    215  * %ecx = curmatch
    216  * %edx = chainlenwmask - i.e., ((chainlen << 16) | wmask)
    217  * %esi = windowbestlen - i.e., (window + bestlen)
    218  * %edi = prev
    219  * %ebp = limit
    220  */
    221 LookupLoop:
    222 		andl	%edx, %ecx
    223 		movzwl	(%edi,%ecx,2), %ecx
    224 		cmpl	%ebp, %ecx
    225 		jbe	LeaveNow
    226 		subl	$0x00010000, %edx
    227 		js	LeaveNow
    228 LoopEntry:	movzwl	-1(%esi,%ecx), %eax
    229 		cmpl	%ebx, %eax
    230 		jnz	LookupLoop
    231 		movl	window(%esp), %eax
    232 		movzwl	(%eax,%ecx), %eax
    233 		cmpl	scanstart(%esp), %eax
    234 		jnz	LookupLoop
    235 
    236 /* Store the current value of chainlen.					*/
    237 
    238 		movl	%edx, chainlenwmask(%esp)
    239 
    240 /* Point %edi to the string under scrutiny, and %esi to the string we	*/
    241 /* are hoping to match it up with. In actuality, %esi and %edi are	*/
    242 /* both pointed (MAX_MATCH_8 - scanalign) bytes ahead, and %edx is	*/
    243 /* initialized to -(MAX_MATCH_8 - scanalign).				*/
    244 
    245 		movl	window(%esp), %esi
    246 		movl	scan(%esp), %edi
    247 		addl	%ecx, %esi
    248 		movl	scanalign(%esp), %eax
    249 		movl	$(-MAX_MATCH_8), %edx
    250 		lea	MAX_MATCH_8(%edi,%eax), %edi
    251 		lea	MAX_MATCH_8(%esi,%eax), %esi
    252 
    253 /* Test the strings for equality, 8 bytes at a time. At the end,
    254  * adjust %edx so that it is offset to the exact byte that mismatched.
    255  *
    256  * We already know at this point that the first three bytes of the
    257  * strings match each other, and they can be safely passed over before
    258  * starting the compare loop. So what this code does is skip over 0-3
    259  * bytes, as much as necessary in order to dword-align the %edi
    260  * pointer. (%esi will still be misaligned three times out of four.)
    261  *
    262  * It should be confessed that this loop usually does not represent
    263  * much of the total running time. Replacing it with a more
    264  * straightforward "rep cmpsb" would not drastically degrade
    265  * performance.
    266  */
    267 LoopCmps:
    268 		movl	(%esi,%edx), %eax
    269 		xorl	(%edi,%edx), %eax
    270 		jnz	LeaveLoopCmps
    271 		movl	4(%esi,%edx), %eax
    272 		xorl	4(%edi,%edx), %eax
    273 		jnz	LeaveLoopCmps4
    274 		addl	$8, %edx
    275 		jnz	LoopCmps
    276 		jmp	LenMaximum
    277 LeaveLoopCmps4:	addl	$4, %edx
    278 LeaveLoopCmps:	testl	$0x0000FFFF, %eax
    279 		jnz	LenLower
    280 		addl	$2, %edx
    281 		shrl	$16, %eax
    282 LenLower:	subb	$1, %al
    283 		adcl	$0, %edx
    284 
    285 /* Calculate the length of the match. If it is longer than MAX_MATCH,	*/
    286 /* then automatically accept it as the best possible match and leave.	*/
    287 
    288 		lea	(%edi,%edx), %eax
    289 		movl	scan(%esp), %edi
    290 		subl	%edi, %eax
    291 		cmpl	$MAX_MATCH, %eax
    292 		jge	LenMaximum
    293 
    294 /* If the length of the match is not longer than the best match we	*/
    295 /* have so far, then forget it and return to the lookup loop.		*/
    296 
    297 		movl	deflatestate(%esp), %edx
    298 		movl	bestlen(%esp), %ebx
    299 		cmpl	%ebx, %eax
    300 		jg	LongerMatch
    301 		movl	windowbestlen(%esp), %esi
    302 		movl	dsPrev(%edx), %edi
    303 		movl	scanend(%esp), %ebx
    304 		movl	chainlenwmask(%esp), %edx
    305 		jmp	LookupLoop
    306 
    307 /*         s->match_start = cur_match;					*/
    308 /*         best_len = len;						*/
    309 /*         if (len >= nice_match) break;				*/
    310 /*         scan_end = *(ushf*)(scan+best_len-1);			*/
    311 
    312 LongerMatch:	movl	nicematch(%esp), %ebx
    313 		movl	%eax, bestlen(%esp)
    314 		movl	%ecx, dsMatchStart(%edx)
    315 		cmpl	%ebx, %eax
    316 		jge	LeaveNow
    317 		movl	window(%esp), %esi
    318 		addl	%eax, %esi
    319 		movl	%esi, windowbestlen(%esp)
    320 		movzwl	-1(%edi,%eax), %ebx
    321 		movl	dsPrev(%edx), %edi
    322 		movl	%ebx, scanend(%esp)
    323 		movl	chainlenwmask(%esp), %edx
    324 		jmp	LookupLoop
    325 
    326 /* Accept the current string, with the maximum possible length.		*/
    327 
    328 LenMaximum:	movl	deflatestate(%esp), %edx
    329 		movl	$MAX_MATCH, bestlen(%esp)
    330 		movl	%ecx, dsMatchStart(%edx)
    331 
    332 /* if ((uInt)best_len <= s->lookahead) return (uInt)best_len;		*/
    333 /* return s->lookahead;							*/
    334 
    335 LeaveNow:
    336 		movl	deflatestate(%esp), %edx
    337 		movl	bestlen(%esp), %ebx
    338 		movl	dsLookahead(%edx), %eax
    339 		cmpl	%eax, %ebx
    340 		jg	LookaheadRet
    341 		movl	%ebx, %eax
    342 LookaheadRet:
    343 
    344 /* Restore the stack and return from whence we came.			*/
    345 
    346 		addl	$LocalVarsSize, %esp
    347 		.cfi_def_cfa_offset 20
    348 		popl	%ebx
    349 		.cfi_def_cfa_offset 16
    350 		popl	%esi
    351 		.cfi_def_cfa_offset 12
    352 		popl	%edi
    353 		.cfi_def_cfa_offset 8
    354 		popl	%ebp
    355 		.cfi_def_cfa_offset 4
    356 .cfi_endproc
    357 match_init:	ret
    358