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/* match.s -- Pentium-optimized version of longest_match()

 * Written for zlib 1.1.2

 * Copyright (C) 1998 Brian Raiter 

 *

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

 * under the terms of the GNU General Public License.

 */

#ifndef NO_UNDERLINE

#define match_init      _match_init

#define longest_match   _longest_match

#endif

#define MAX_MATCH       (258)

#define MIN_MATCH       (3)

#define MIN_LOOKAHEAD   (MAX_MATCH + MIN_MATCH + 1)

#define MAX_MATCH_8     ((MAX_MATCH + 7) & ~7)

/* stack frame offsets */

#define wmask                   0        /* local copy of s->wmask       */

#define window                  4       /* local copy of s->window      */

#define windowbestlen           8       /* s->window + bestlen          */

#define chainlenscanend         12      /* high word: current chain len */

                                        /* low word: last bytes sought  */

#define scanstart               16      /* first two bytes of string    */

#define scanalign               20      /* dword-misalignment of string */

#define nicematch               24      /* a good enough match size     */

#define bestlen                 28      /* size of best match so far    */

#define scan                    32      /* ptr to string wanting match  */

#define LocalVarsSize           (36)

/*      saved ebx               36 */

/*      saved edi               40 */

/*      saved esi               44 */

/*      saved ebp               48 */

/*      return address          52 */

#define deflatestate            56      /* the function arguments       */

#define curmatch                60

/* Offsets for fields in the deflate_state structure. These numbers

 * are calculated from the definition of deflate_state, with the

 * assumption that the compiler will dword-align the fields. (Thus,

 * changing the definition of deflate_state could easily cause this

 * program to crash horribly, without so much as a warning at

 * compile time. Sigh.)

 */

/* All the +zlib1222add offsets are due to the addition of fields

 *  in zlib in the deflate_state structure since the asm code was first written

 * (if you compile with zlib 1.0.4 or older, use "zlib1222add equ (-4)").

 * (if you compile with zlib between 1.0.5 and 1.2.2.1, use "zlib1222add equ 0").

 * if you compile with zlib 1.2.2.2 or later , use "zlib1222add equ 8").

 */

#define zlib1222add             (8)

#define dsWSize                 (36+zlib1222add)

#define dsWMask                 (44+zlib1222add)

#define dsWindow                (48+zlib1222add)

#define dsPrev                  (56+zlib1222add)

#define dsMatchLen              (88+zlib1222add)

#define dsPrevMatch             (92+zlib1222add)

#define dsStrStart              (100+zlib1222add)

#define dsMatchStart            (104+zlib1222add)

#define dsLookahead             (108+zlib1222add)

#define dsPrevLen               (112+zlib1222add)

#define dsMaxChainLen           (116+zlib1222add)

#define dsGoodMatch             (132+zlib1222add)

#define dsNiceMatch             (136+zlib1222add)

.file "match.S"

.globl  match_init, longest_match

.text

/* uInt longest_match(deflate_state *deflatestate, IPos curmatch) */

longest_match:

/* Save registers that the compiler may be using, and adjust %esp to    */

/* make room for our stack frame.                                       */

                pushl   %ebp

                pushl   %edi

                pushl   %esi

                pushl   %ebx

                subl    $LocalVarsSize, %esp

/* 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).                                             */

                movl    deflatestate(%esp), %edx

                movl    curmatch(%esp), %ecx

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

                movl    dsNiceMatch(%edx), %eax

                movl    dsLookahead(%edx), %ebx

                cmpl    %eax, %ebx

                jl      LookaheadLess

                movl    %eax, %ebx

LookaheadLess:  movl    %ebx, nicematch(%esp)

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

                movl    dsWindow(%edx), %esi

                movl    %esi, window(%esp)

                movl    dsStrStart(%edx), %ebp

                lea     (%esi,%ebp), %edi

                movl    %edi, scan(%esp)

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

/* dword-aligned.                                                       */

                movl    %edi, %eax

                negl    %eax

                andl    $3, %eax

                movl    %eax, scanalign(%esp)

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

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

                movl    dsWSize(%edx), %eax

                subl    $MIN_LOOKAHEAD, %eax

                subl    %eax, %ebp

                jg      LimitPositive

                xorl    %ebp, %ebp

LimitPositive:

/* unsigned chain_length = s->max_chain_length;                         */

/* if (s->prev_length >= s->good_match) {                               */

/*     chain_length >>= 2;                                              */

/* }                                                                    */

                movl    dsPrevLen(%edx), %eax

                movl    dsGoodMatch(%edx), %ebx

                cmpl    %ebx, %eax

                movl    dsMaxChainLen(%edx), %ebx

                jl      LastMatchGood

                shrl    $2, %ebx

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 scanend  */

/* scanend value, which it will always accompany.                       */

                decl    %ebx

                shll    $16, %ebx

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

                movl    dsPrevLen(%edx), %eax

                movl    %eax, bestlen(%esp)

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

                addl    %eax, %esi

                movl    %esi, windowbestlen(%esp)

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

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

                movw    (%edi), %bx

                movw    %bx, scanstart(%esp)

                movw    -1(%edi,%eax), %bx

                movl    %ebx, chainlenscanend(%esp)

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

/* uInt wmask = s->w_mask;                                              */

                movl    dsPrev(%edx), %edi

                movl    dsWMask(%edx), %edx

                mov     %edx, wmask(%esp)

/* Jump into the main loop.                                             */

                jmp     LoopEntry

.balign 16

/* 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 = chainlenscanend - i.e., ((chainlen << 16) | scanend)

 * %ecx = curmatch

 * %edx = curmatch & wmask

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

 * %edi = prev

 * %ebp = limit

 *

 * Two optimization notes on the choice of instructions:

 *

 * The first instruction uses a 16-bit address, which costs an extra,

 * unpairable cycle. This is cheaper than doing a 32-bit access and

 * zeroing the high word, due to the 3-cycle misalignment penalty which

 * would occur half the time. This also turns out to be cheaper than

 * doing two separate 8-bit accesses, as the memory is so rarely in the

 * L1 cache.

 *

 * The window buffer, however, apparently spends a lot of time in the

 * cache, and so it is faster to retrieve the word at the end of the

 * match string with two 8-bit loads. The instructions that test the

 * word at the beginning of the match string, however, are executed

 * much less frequently, and there it was cheaper to use 16-bit

 * instructions, which avoided the necessity of saving off and

 * subsequently reloading one of the other registers.

 */

LookupLoop:

                                                        /* 1 U & V  */

                movw    (%edi,%edx,2), %cx              /* 2 U pipe */

                movl    wmask(%esp), %edx               /* 2 V pipe */

                cmpl    %ebp, %ecx                      /* 3 U pipe */

                jbe     LeaveNow                        /* 3 V pipe */

                subl    $0x00010000, %ebx               /* 4 U pipe */

                js      LeaveNow                        /* 4 V pipe */

LoopEntry:      movb    -1(%esi,%ecx), %al              /* 5 U pipe */

                andl    %ecx, %edx                      /* 5 V pipe */

                cmpb    %bl, %al                        /* 6 U pipe */

                jnz     LookupLoop                      /* 6 V pipe */

                movb    (%esi,%ecx), %ah

                cmpb    %bh, %ah

                jnz     LookupLoop

                movl    window(%esp), %eax

                movw    (%eax,%ecx), %ax

                cmpw    scanstart(%esp), %ax

                jnz     LookupLoop

/* Store the current value of chainlen.                                 */

                movl    %ebx, chainlenscanend(%esp)

/* 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).                           */

                movl    window(%esp), %esi

                movl    scan(%esp), %edi

                addl    %ecx, %esi

                movl    scanalign(%esp), %eax

                movl    $(-MAX_MATCH_8), %edx

                lea     MAX_MATCH_8(%edi,%eax), %edi

                lea     MAX_MATCH_8(%esi,%eax), %esi

/* 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:

                movl    (%esi,%edx), %eax

                movl    (%edi,%edx), %ebx

                xorl    %ebx, %eax

                jnz     LeaveLoopCmps

                movl    4(%esi,%edx), %eax

                movl    4(%edi,%edx), %ebx

                xorl    %ebx, %eax

                jnz     LeaveLoopCmps4

                addl    $8, %edx

                jnz     LoopCmps

                jmp     LenMaximum

LeaveLoopCmps4: addl    $4, %edx

LeaveLoopCmps:  testl   $0x0000FFFF, %eax

                jnz     LenLower

                addl    $2, %edx

                shrl    $16, %eax

LenLower:       subb    $1, %al

                adcl    $0, %edx

/* 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     (%edi,%edx), %eax

                movl    scan(%esp), %edi

                subl    %edi, %eax

                cmpl    $MAX_MATCH, %eax

                jge     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.           */

                movl    deflatestate(%esp), %edx

                movl    bestlen(%esp), %ebx

                cmpl    %ebx, %eax

                jg      LongerMatch

                movl    chainlenscanend(%esp), %ebx

                movl    windowbestlen(%esp), %esi

                movl    dsPrev(%edx), %edi

                movl    wmask(%esp), %edx

                andl    %ecx, %edx

                jmp     LookupLoop

/*         s->match_start = cur_match;                                  */

/*         best_len = len;                                              */

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

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

LongerMatch:    movl    nicematch(%esp), %ebx

                movl    %eax, bestlen(%esp)

                movl    %ecx, dsMatchStart(%edx)

                cmpl    %ebx, %eax

                jge     LeaveNow

                movl    window(%esp), %esi

                addl    %eax, %esi

                movl    %esi, windowbestlen(%esp)

                movl    chainlenscanend(%esp), %ebx

                movw    -1(%edi,%eax), %bx

                movl    dsPrev(%edx), %edi

                movl    %ebx, chainlenscanend(%esp)

                movl    wmask(%esp), %edx

                andl    %ecx, %edx

                jmp     LookupLoop

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

LenMaximum:     movl    deflatestate(%esp), %edx

                movl    $MAX_MATCH, bestlen(%esp)

                movl    %ecx, dsMatchStart(%edx)

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

/* return s->lookahead;                                                 */

LeaveNow:

                movl    deflatestate(%esp), %edx

                movl    bestlen(%esp), %ebx

                movl    dsLookahead(%edx), %eax

                cmpl    %eax, %ebx

                jg      LookaheadRet

                movl    %ebx, %eax

LookaheadRet:

/* Restore the stack and return from whence we came.                    */

                addl    $LocalVarsSize, %esp

                popl    %ebx

                popl    %esi

                popl    %edi

                popl    %ebp

match_init:     ret