argh! count number of full stops??

VB Code:

Public Function Sisic4(pStr As Long, pFind As Long, lenStr As Long, lenFind As Long) As Long
 
    Dim i As Long
    Dim j As Long
    Dim Flag As Long
    
    CopyMemory BufStr(0), ByVal pStr, lenStr
    CopyMemory BufFind(0), ByVal pFind, lenFind
    
    i = lenStr - 1
    
    If lenFind = 2 Then
        Do Until i < lenFind
            If BufStr(i - 1) = BufFind(0) Then
                Sisic4 = Sisic4 + 1
            End If
            i = i - 2
        Loop
    Else
        Do Until i < lenFind
            Flag = 0
            j = lenFind - 1
            Do Until j < 0
                If Not (BufStr(i - (lenFind - j)) = BufFind(j - 1)) Then
                    Flag = -1
                    Exit Do
                End If
                j = j - 2
            Loop
            If Flag = 0 Then
                Sisic4 = Sisic4 + 1
            End If
            i = i - 2
        Loop
    End If
    
End Function

Removing the for/loops makes it go faster!!
Sisic3=469, Sisic4=438

It's more efficient to pass Long values ByVal instead of ByRef because ByRef results in an indirection whereas ByVal doesn't. Seeing as a pointer is the same size as a Long anyway, you lose instead of gaining. I deleted the benchmarking code so see if that gives any increase in times.

No! It makes it slower

Sisic3=475
Sisic4=544

Did you put the code in the form. I just realised it has to do a vtable lookup every time it calls the function, so I put it in a module and it is much faster... in fact your Sisic3 function is faster than Sisic4 that you posted in #41.

ByVal is faster... told you :D

InStrCount3: 375 ms
Sisic3: 344 ms
Sisic4 with ByRef: 343 ms
Sisic4 with ByVal: 313 ms

Yeah I put the function in the form :blush:

I managed to get mine to the same speed as yours, they are now basically exactly the same code :D

It is indeed faster to pass the string length as a parameter, and to use module-level buffers instead of statics.

So far I can't really think of any other optimisations to do.

I was surprised by the minor increase in speed from dumping the for/loops.

Quote:

---

Originally Posted by penagate

I managed to get mine to the same speed as yours, they are now basically exactly the same code :D

It is indeed faster to pass the string length as a parameter, and to use module-level buffers instead of statics.

So far I can't really think of any other optimisations to do.

---

I quite often allocate myself 2k of heap at app startup, and then just use that as a workspace. The main problem is, of course, dereferencing. CopyMemory is fine, but for dereferencing it's pretty slow .. .

I toyed with the idea of using HeapAlloc, but then the thought of calling CopyMemory on every loop iteration through the string just put me right off.

I tried it and it was slower.

Any ideas why for/loops are slower than do/loops. I have been under the impression that for/loops were faster.

Can't remember where I got that idea, from!

Neither can I, but I dunno why yours got faster. I tried it too and it over several runs it made no (noticable) difference either way.

BTW, I take that back about not thinking of any other optimisations to do :D

VB Code:

Function InStrCount4( _
    ByVal pszString As Long, _
    ByVal pszFind As Long, _
    ByVal pchSearchChar As Byte, _
    ByVal lStringLen As Long, _
    ByVal lFindLen As Long _
) As Long
Dim i               As Long
Dim j               As Long
 
    CopyMemory mchBuf(0), ByVal pszString, lStringLen
 
    If (lFindLen = 2) Then
        If (pchSearchChar = 0) Then _
            CopyMemory pchSearchChar, ByVal pszFind, 1
        Do
            If (mchBuf(i) = pchSearchChar) Then _
                InStrCount4 = InStrCount4 + 1
            i = i + 2
        Loop Until i = lStringLen
 
      Else
        CopyMemory mchFind(0), ByVal pszFind, lFindLen
        Do
            Do
                If (mchBuf(i + j) <> mchFind(j)) Then
                    Exit Do
                  Else
                    If (j = lFindLen) Then _
                        InStrCount4 = InStrCount4 + 1
                End If
                j = j + 2
            Loop Until j = lFindLen
            i = i + lFindLen
        Loop Until i = lStringLen
    End If
End Function

Results:
Sisic3: 328 ms
Sisc4 (ByVal): 312 ms
InStrCount4: 282 ms

:D :D

Yeah that's pretty fast. Haven't had time to look at it properly (and probably won't) What have you done? (I haven't got your intermediate code!)

Got rid of Statics, passed string lengths as parameters, that made it as fast as yours.

Added a choice between passing a pointer to find string buffer, and passing a byte character directly, that made it faster than yours.

Oh yeah. That's pretty cool.

If the CopyMemory is typelib defined - then that will make it faster, too (I believe - I haven't tried it yet - but might do some point this week)

according to MSDN Help using ordinal numbers is supposed to be faster than function names. However, I tried, and it made no difference whatsoever. You'd think it would be handled the same way by the linker anyway, so I fail to see the logic behind that one.

VB Code:

[
    uuid(842b47f0-0b27-11da-8cd6-0800200c9a66),
    version(0.1),
    helpstring("Win32 API Kernel32.DLL")
]
library Win32Stuff
{
    importlib("stdole2.tlb");
 
    [dllname("kernel32")]
 
    module kernel32
    {
        [
            entry("RtlMoveMemory")
        ]
        VOID CopyMemory ([in,out] LONG* lpDestination, [in,out] LONG* lpSource, [in] LONG Length);
    }
}

Compile this using MkTypLib (you may need to set a few path environment variables) remove 'CopyMemory' from your declare list and reference the compiled type library.

I get around 18% performance boost.

VB Code:

Public Function Sisic4(ByVal pStr As Long, ByVal pFind As Long, ByVal lenStr As Long, ByVal lenFind As Long) As Long
 
    Dim i As Long
    Dim j As Long
    Dim Flag As Long
    
    CopyMemory VarPtr(BufStr(0)), ByVal pStr, ByVal lenStr
    CopyMemory VarPtr(BufFind(0)), ByVal pFind, ByVal lenFind
    
    i = lenStr - 1
    
    If lenFind = 2 Then
        Do Until i < lenFind
            If BufStr(i - 1) = BufFind(0) Then
                Sisic4 = Sisic4 + 1
            End If
            i = i - 2
        Loop
    Else
        Do Until i < lenFind
            Flag = 0
            j = lenFind - 1
            Do Until j < 0
                If Not (BufStr(i - (lenFind - j)) = BufFind(j - 1)) Then
                    Flag = -1
                    Exit Do
                End If
                j = j - 2
            Loop
            If Flag = 0 Then
                Sisic4 = Sisic4 + 1
            End If
            i = i - 2
        Loop
    End If
    
End Function

.. note the varptr function is used to get the ptr to the first array entry.

Compiled the tlb, but I get a Type Mismatch on the VarPtr parameter?

Weird!

Have you commented out the existing CopyMemory declare?

Yup.

It likes it when I remove all the ByVal keywords, but then when I run my function, it bombs out with a subscript out of range error. Further inspection showed that my i variable had been overwritten with gibberish :sick: