Fastest possible string search

[Lance Edmonds]

a$ = PEEK$(VARPTR(ByteArray(0)), lengthofarray&)

------------------
Lance
PowerBASIC Support
mailto:[email protected][email protected]</A>

[Borje Hagsten]

Okay, tested on relatively slow machine. ScanString is a bit faster
and seems to work fine. Must observe results though, since they are
zero based and returns -1 on failure, unlike INSTR's 1-based and zero
on failure. Very interesting code, Hutch - I like it a lot.

' Processor = 266 MHz
' MainStr   = 80KB text file.
' wrd()     = array of 3000 different phrases, ranging from 2 - 37 bytes long
' NumRecs   = UBOUND(wrd)
'
' Average results from multiple scans on file
' result INSTR, 603 hits/scan in 6.39 sec.
' result myINSTR, 603 hits/scan in 6.25 sec.
' result ScanString, 603 hits/scan in 5.58 sec.
' test code as follows: (here for ScanString, but same kind was used for all)
' ------------------------------------------------------------------------------------
  LOCAL c AS LONG, mPtr AS LONG, sPtr AS LONG, mLen AS LONG, sLen AS LONG, _
        hit AS LONG, lRes AS LONG, tc1 AS LONG, tc2 AS LONG
  tc1  = GetTickCount()
  mPtr = STRPTR(MainStr)
  mLen = LEN(MainStr)
 
  FOR c = 0 TO Numrecs
     SearchStr = wrd(c)
     sPtr = STRPTR(SearchStr)
     sLen = LEN(SearchStr)
     lRes = ScanString(0, mPtr, mLen, sPtr, sLen)
     IF lRes > -1 THEN
        INCR hit
        DO
           lRes = ScanString(lRes + sLen, mPtr, mLen, sPtr, sLen)
           IF lRes > -1 THEN INCR hit
        LOOP WHILE lRes > -1
     END IF
  NEXT
 
  tc2 = GetTickCount() - tc1 
  MSGBOX STR$(hit) + "  " + FORMAT$(tc2/1000, "0.0000") + " Pos: " + FORMAT$(lRes), %MB_OK OR %MB_ICONINFORMATION, "ScanString"
  ' ------------------------------------------------------------------------------------

------------------

[Nathan Evans]

Borje/Steve, i had a go with the code you kindly posted, and have had some success.

I am inputting a 500kb file.. and searched it for 15 strings.

The total process, per GetTickCount, took 40ms. This is MUCH faster than
a previous implementation i did in VisualBasic using it's InStr, if i recall
it was around 300ms..

However much i would like to use this code. I do not believe 40ms is fast enough,
when searching for 15 strings.

May i ask a question?..

Is the speed of the ScanString function affected by the length of
the SearchStr ? ie: will using longer search strings increase or decrease
the speed of the search ?

I will keep fiddling with this code, and see if i can make it any more efficient.

Thank you very much in guiding me through this.

regards
- Nathan.

[Steve Hutchesson]

Borje,

Thanks for testing the algo, this PIII I use has so many "unusual"
effects when timing algorithms that it can nearly drive you nuts.

It looks like the ScanString algo is still a bit too slow in its
branching code so i will see if I can find a way to get its branch
speed up a bit.

Nathan,

You should not have to do a conversion to a basic dynamic string
to use the two algorithms that I have pasted in, they work directly
in addresses and the way you load the file using the API function
should give you the start address and the file length.

To get your speed up, I would suggest that you make an array of the
search patterns you wish to use and store their lengths as well so
that this information is available when you start the scanning for
each file. The idea is to load the search patterns at startup so that
you have both their addresses and their lengths.

When you load the file to scan from disk, you will have the start address
and length and you can loop through the array of patterns with very little
overhead once you set it up.

The length of the pattern being searched is not that important in most
instances, the scanners will stop testing after the first mismatch and
continue with the main scan. If the Boyer Moore algo runs OK, it
will actually get faster as the pattern gets longer.

Regards,

[email protected]

------------------

[Nathan Evans]

Morning

Steve,
I have a LoadDB sub which is called in PBMAIN, this loads a currently
small definitions file of 30 into 2 dimensions string array. One of the
subscripts in this contains a hexidecimal search string. Still in the
LoadDB sub, i convert these Hexidecimal strings using Chr and Val into
normal ASCII. The search array of strings is then loaded into memory.

Next i have a 'AnalyseFile' function. This opens the file specified in
the 'szFile as String' parameter of the function. Then starts a For Next loop
to analyse that file for each search string in the 2D search string array
that was created from LoadDB.

If i use the normal InStr function that comes with PB, this will
analyse a 3.2mb BMP file for all 30 search strings in 651 ms.
I used GetTickCount and a bit a math to work out a Scan Speed in Mb/sec.
And Calculated 6Mb/sec - which is awfully slow


Right now, i'm working with your ScanString function. But it doesn't find anything,
even if they are valid strings as found in the file..

 LOCAL tC AS LONG, enumI AS LONG
 LOCAL retVal AS LONG, MainStr AS STRING, SearchStr AS STRING  

    SearchStr = ayFileDef(enumI, 2)
    retVal = ScanString( 0, STRPTR(MainStr), LEN(MainStr), STRPTR(SearchStr), LEN(SearchStr) )
    'retVal = INSTR( 1, MainStr, SearchStr )

I'm using the exact same ScanString as you posted.
It will always return -1, what am i doing wrong?

Thanks very much and bare with me

Best,

-Nathan.




[This message has been edited by Nathan Evans (edited July 01, 2001).]

[Steve Hutchesson]

Nathan,

This test code below is running 100 iterations through win32api.inc in about
700 ms on my PIII so it is searching about 75 meg in 700 ms.

    Open "win32api.inc" for Binary as #1
      Get$ #1,lof(1),a$
    Close #1
  
    b$ = "' ** VERSION.DLL Declares" ' << almost at the end
  
    LOCAL cnt as LONG
    cnt = 0
  
    tc& = GetTickCount
  
    ap&  = StrPtr(a$)
    aln& = len(a$)
    bpt& = StrPtr(b$)
    bln& = len(b$)
  
    Do
      rv& = ScanString(0,ap&,aln&,bpt&,bln&)
      ! inc cnt
    loop while cnt < 100
  
    tc2& = GetTickCount - tc&
  
    MessageBox hWin,ByCopy str$(rv&),ByCopy str$(tc2&), _
               %MB_OK or %MB_ICONINFORMATION

I would make sure that what you are passing to the "ScanString" function
is correct. Perhaps you need a 3 dimensional array with STRING, ADDRESS and
LENGTH so that you can load the source file and just loop through it.
Converting each time you run a string is a lot slower, far better to have them
all preloaded so that when you do the scan, they are ready.

Regards,

[email protected]

------------------

[Nathan Evans]

Steve,

I tried the example you posted.

The tc2& variable would return 0 at the end of the test..
The rv& variable would hold 622 at the end of the test..

I changed the search string to: ' Last Update: August 22, 1999
which is right near the top of the file, and this returned 622 also.

Am i doing something drastically wrong??

- Nathan

[This message has been edited by Nathan Evans (edited July 01, 2001).]

[Lance Edmonds]

Something is obviously wrong... post the entire source code you are using, and maybe we (or Steve!) can spot something...


------------------
Lance
PowerBASIC Support
mailto:[email protected][email protected]</A>

[Steve Hutchesson]

Nathan,

Here is a quick test piece that does the type of searching you
require. This runs 25 iterations of win32api.inc in about 150ms
on my PIII with 25 different patterns searched for in the same
source file. About 125 meg/sec which is probably in the ball park
in terms of the speed you require.

              LOCAL fl as LONG
              redim patterns$(25)
  
              Open "win32api.inc" for Binary as #1
                fl = lof(1)
                Get$ #1,fl,a$
              Close #1
  
              patterns$(0)  = "VerQueryValue"
              patterns$(1)  = "GetFileVersionInfo"
              patterns$(2)  = "GetFileVersionInfoSize"
              patterns$(3)  = "VerInstallFile"
              patterns$(4)  = "VerFindFile"
              patterns$(5)  = "SystemTimeToVariantTime"
              patterns$(6)  = "VariantTimeToSystemTime"
              patterns$(7)  = "VarDateFromStr"
              patterns$(8)  = "WinExecError"
              patterns$(9)  = "SHFreeNameMappings"
              patterns$(10) = "DragFinish"
              patterns$(11) = "DragAcceptFiles"
              patterns$(12) = "Shell_NotifyIcon"
              patterns$(13) = "ShellExecute"
              patterns$(14) = "ShellAbout"
              patterns$(15) = "SHFormatDrive"
              patterns$(16) = "SHGetNewLinkInfo"
              patterns$(17) = "SHGetFileInfo"
              patterns$(18) = "SHFileOperation"
              patterns$(19) = "SHAppBarMessage"
              patterns$(20) = "FindExecutable"
              patterns$(21) = "FindEnvironmentString"
              patterns$(22) = "ExtractIconEx"
              patterns$(23) = "ExtractIcon"
              patterns$(24) = "ExtractAssociatedIcon"
  
              aln& = len(a$)
  
              LOCAL cnt as LONG
              cnt = 0
  
              tc& = GetTickCount
  
              Do
  
              rv& = ScanString(0,StrPtr(a$),aln&, _
                               StrPtr(patterns$(cnt)),len(patterns$(cnt)))
            ' --------------------------------------
              SetWindowText hWnd,ByCopy str$(rv&)
            ' --------------------------------------
              ! inc cnt
              Loop while cnt < 25
  
              tc2& = GettickCount - tc&
  
              MessageBox hWin,ByCopy str$(rv&),ByCopy str$(tc2&), _
                         %MB_OK or %MB_ICONINFORMATION

Regards,

[email protected]

------------------

[Nathan Evans]

Steve, that code seems to be working. It returns the correct location
for each of them strings.

Lance, i started an entirely new project, pasted in the ScanString function,
created a PBMAIN with the previous example Steve posted - but that would always return
622 no matter what i searched for.


Steve, have you tested this code with Binary files? ie: EXEs.
No matter what i search for in a binary file, it will return -1.

You are right though, these Boyer Moore algorithms are damn fast!!

Many thanks to you both.

- Nathan.

[Lance Edmonds]

I changed the code to load SHELL32.DLL (OPEN "C:\WINNT5\SYSTEM32\SHELL32.DLL" FOR BINARY AS #1) and ran Steves code above... it works fine for me...

My K6/266 (with an MP3 player running and a bunch of other apps going too), it did all 25 searches in SHELL32.DLL in 801mS-841mS, and found all of the API names that are actually contained in SHELL32.DLL.

I can only suggest that you relook at your code or post it here...

------------------
Lance
PowerBASIC Support
mailto:[email protected][email protected]</A>

[Lance Edmonds]

I played with this a little further and the following code is the fruits of my efforts.

When run on the WIN32API.INC file, INSTR() beats the BM algorithm code every time on my Win2K PC, at a fairly consistent 1-30% (worst:best).

Get rid of the B$ allocation within the loops to greatly speed this up too... on my PC, the MB loop runs in 300-400ms, and the INSTR loop around 30% faster.

Here is the code I used:

#COMPILE EXE
#INCLUDE "WIN32API.INC"
'##########################################################################

FUNCTION ScanString(BYVAL startpos AS LONG, _
                      BYVAL source   AS LONG, BYVAL lnsrc AS LONG, _
                      BYVAL pattern  AS LONG, BYVAL lnpatn AS LONG) AS LONG

      #REGISTER NONE

      ! mov edi, pattern
      ! mov al, [edi]       ; get 1st byte

      ! mov esi, source
      ! mov ecx, lnsrc
      ! add esi, ecx
      ! neg ecx
      ! add ecx, startpos

      ! dec lnpatn

      ! jmp main_loop

    ' %%%%%%%%%%%%%%%%%%%%%%%%%%%%

    pre_loop:
      ! pop ecx
      ! inc ecx

    main_loop:
    ' ------------
    ' unroll by 2
    ' ------------
      ! cmp al, [esi+ecx]
      ! je pre_sub
      ! inc ecx
      ! jz nMatch

      ! cmp al, [esi+ecx]
      ! je pre_sub
      ! inc ecx
      ! jnz main_loop
    ' ------------
      ! jmp nMatch

    pre_sub:
      ! push ecx
      ! mov edi, pattern
      ! mov ebx, lnpatn

    sub_loop:
      ! mov ah, [esi+ecx+1]
      ! cmp ah, [edi+1]
      ! jne pre_loop
      ! inc ecx
      ! inc edi
      ! dec ebx
      ! jnz sub_loop

    ' %%%%%%%%%%%%%%%%%%%%%%%%%%%%

      ! pop eax
      ! add eax, lnsrc
      ! jmp Outa_Here

    nMatch:
      ! mov eax, -1

    Outa_Here:
      ! mov FUNCTION, eax

END FUNCTION

' ########################################################################

FUNCTION PBMAIN
    LOCAL fl AS LONG
    REDIM patterns$(25)

    OPEN "F:\PBDLL60\WINAPI\win32api.inc" FOR BINARY AS #1
'    OPEN "C:\WINNT5\SYSTEM32\SHELL32.DLL" FOR BINARY AS #1
    fl = LOF(1)
    GET$ #1,fl,a$
    CLOSE #1

    patterns$(0)  = "VerQueryValue"
    patterns$(1)  = "GetFileVersionInfo"
    patterns$(2)  = "GetFileVersionInfoSize"
    patterns$(3)  = "VerInstallFile"
    patterns$(4)  = "VerFindFile"
    patterns$(5)  = "SystemTimeToVariantTime"
    patterns$(6)  = "VariantTimeToSystemTime"
    patterns$(7)  = "VarDateFromStr"
    patterns$(8)  = "WinExecError"
    patterns$(9)  = "SHFreeNameMappings"
    patterns$(10) = "DragFinish"
    patterns$(11) = "DragAcceptFiles"
    patterns$(12) = "Shell_NotifyIcon"
    patterns$(13) = "ShellExecute"
    patterns$(14) = "ShellAbout"
    patterns$(15) = "SHFormatDrive"
    patterns$(16) = "SHGetNewLinkInfo"
    patterns$(17) = "SHGetFileInfo"
    patterns$(18) = "SHFileOperation"
    patterns$(19) = "SHAppBarMessage"
    patterns$(20) = "FindExecutable"
    patterns$(21) = "FindEnvironmentString"
    patterns$(22) = "ExtractIconEx"
    patterns$(23) = "ExtractIcon"
    patterns$(24) = "ExtractAssociatedIcon"

    aln& = LEN(a$)

    LOCAL cnt AS LONG
    cnt = 0
    b$ = ""

    tc2& = GetTickCount
    DO

        rv& = ScanString(0,STRPTR(a$),aln&, _
            STRPTR(patterns$(cnt)),LEN(patterns$(cnt)))
        b$ = b$ + STR$(rv&)
        ! inc cnt
    LOOP WHILE cnt < 25
    tc2& = GettickCount - tc2&

    cnt = 0
    b$ = b$ + $CRLF
    tc& = GetTickCount
    DO
        rv& = INSTR(a$, patterns$(cnt))
        b$ = b$ + STR$(rv&)
        ! inc cnt
    LOOP WHILE cnt < 25
    
    tc& = GetTickCount - tc&
    
    b$ = B$ + $CRLF + "INSTR/MB = " + STR$(tc&/tc2&)

    MessageBox hWin&,BYVAL STRPTR(B$),"MB=" + STR$(tc2&) + "  INSTR=" + STR$(tc&), _
        %MB_OK OR %MB_ICONINFORMATION

END FUNCTION

------------------
Lance
PowerBASIC Support
mailto:[email protected][email protected]</A>

[Nathan Evans]

Lance, i'm just trying to get this working in my main project.

I dont like using variables like: rv&
So i'm defining them as LOCAL.

Just to be clear, a & signifies a LONG right ?

[Nathan Evans]

Lance,

Hmm.. Once i've got my BM working, i'll be able to use both.

I know InStr works better with smaller files..
And BM with larger files.

So i could easily put a If statement that chooses which method to
use depending on the Filesize.

I will have to do some testing across multiple platforms to find
a good value as to when BM should be run.

Thanks.

[Lance Edmonds]

Does my (abeit untidy) test code above run for you? (Obviously it will need the paths edited accordingly), but if it runs then you are half-way to getting it working in your real program.

Yes, the "&" type-specifier suffix means a LONG integer.

This thread is now getting to long and is closed... if you require more help with this item, please start a new thread and include a link to this thread.

Thanks!



------------------
Lance
PowerBASIC Support
mailto:[email protected][email protected]</A>