Optimization For Speed -- Any Thoughts?

[Andrew Peskin]

I have a relatively small function, which my profiler has indicated is taking a majority of the time and was hoping to optimize it some. Looking over some of the recent posts, I have been able to make some progress but would like to see if this can be sped up any more. What the function does is extract the value of two bits from a passed in byte. The code as it is now is:

Private Function Extract_TWO_Bits(TheBYTE As Byte, Position As Integer) As Integer


	On Position GoTo Zero, Two, Four, Six
                     
	Zero:
	    '// Isolates BITS 0 and 1
	    Extract_TWO_Bits = (TheBYTE And 3)          '// 3 = &H3
	    Exit Function
                     
	Two:
	    '// Isolates BITS 2 and 3
	    Extract_TWO_Bits = (TheBYTE And 12) \ 4    '// 12 = &HC
	    Exit Function
                    
	Four:
	    '// Isolates BITS 4 and 5
	    Extract_TWO_Bits = (TheBYTE And 48) \ 16     '// 48 = &H30
	    Exit Function
                     
	Six:
	    '// Isolates BITS 6 and 7
	    Extract_TWO_Bits = TheBYTE \ 64
	    Exit Function

End Function

Changing from a SELECT CASE to the On ... GoTo made a big improvement. From looking at this code is there anything else I can do to make this faster?

Also, in another function (which now takes most of the time), the two lines consuming most clock cycles are:

            INTPortion = Int(RAWPrice / 100#)
            DECPortion = ((RAWPrice / 100#) - INTPortion) * 100#

Is there any way to speed these up at all?

I am looking forward dot your responses. Many thanks in advance.

Best regards,

Andrew Peskin
[email protected]


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[This message has been edited by Andrew Peskin (edited March 21, 2001).]

[Russ Srole]

Andrew,

Use an integer divide:
IntPortion = RawPrice \ 100
And a Mod
DecPortion = (RawPrice mod 100) * 100

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[Bern Ertl]

Andrew,

#1) Have you tried using SHIFT RIGHT instead of \ ? I don't know
if it is faster or not, but you might try testing it.

#2) INTPortion = FIX( RAWPrice) ?
DECPortion = FRAC( RAWPrice) ?



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Bernard Ertl

[Mike Burns]

On the lines of Bern's suggestion this gets rid of the Goto's ..
it might be faster

Replace the all the code with

' shifts the desired bits to bits 0,1 .. mask off other bits
Function = SHIFT RIGHT TheByte, (position*2)-2) AND &H03

I am not sure of the syntax but that is the idea.

Mike

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[Peter Manders]

Good idea Mike, after that you can forget about calling a FUNCTION and just put that line whereever it's needed.
That way you'd eliminate the function calling overhead.

I was going to suggest using only LONGs, also as parameters but there's no need if you can eliminate the function altogether.


Peter.


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[email protected]

[Andrew Peskin]

Originally posted by Mike Burns:
On the lines of Bern's suggestion this gets rid of the Goto's ..
it might be faster

Replace the all the code with

' shifts the desired bits to bits 0,1 .. mask off other bits
Function = SHIFT RIGHT TheByte, (position*2)-2) AND &H03

I am not sure of the syntax but that is the idea.

Mike

What would the sytax be for this? Would it be able to extract the 2 specific bits you wanted based on position? Anyone know how to write this?

Andrew



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[Scott Wolfington]

Hi Andrew!

Sorry I don't have any advice to offer you on this, but I'm interested
in knowing what your "profiler" app is. What is the name of it? Is it
a part of PB? Thanks in advance!

Regards,
Scott


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Scott Wolfington
http://www.boogietools.com


[This message has been edited by Scott Wolfington (edited March 05, 2003).]

[Andrew Peskin]

Here is another line which is reported to take 76 Clock Ticks, is there any way to speed it up?

FUNCTION = ((RAWPrice& / (10& ^ ConvFact&)) / MinTick#)

Anyone have any ideas on this?

Many thanks.

Andrew

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[Andrew Peskin]

Originally posted by Scott Wolfington:
Hi Andrew!

Sorry I don't have any advice to offer you on this, but I'm interested
in knowing what your "profiler" app is. What is the name of it? Is it
a part of PB? Thanks in advance!

Regards,
Scott

I use a multi-step process for trying to benchmark/analyze code I write to determine where the bottlenecks are. I first have a simple procedure that I can place at the beginning and ending of each function call which logs time spent in each. Once certain functions are flagged as taking the most time, I compile the application (or a subset of it) in Visual Basic creating a Symbolic Debug File (I rarely have to make minor modifications and usually have no problems cross compiling my code). I then use Intel's VTune performance analyzer to profile the application. I realize that VB and PB are drastically different compilers, but after first using the information in the output log from running the PB app, I can then more precisely hone in on the problem areas with VTune in the VB app. Usually once I make changes and get performance increases on the specific lines it flags, I do see an improvement in my PB application. I realize that this is sort of a long way around approach, but it works pretty nicely for me.

Hope this was helpful. If you are interested, Email me directly for more information.

Andrew



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[Mike Burns]

Andrew,

Since SHIFT is a statement and it appears to destroy (alter)
the operand you might need to

A) Pass TheByte BYVAL (I think that will pass a copy of TheByte)
and
B) Use 2 lines in the function

Function Extract_Two_Bits(BYVAL TheByte As Byte, position as Integer) as Integer
    SHIFT RIGHT TheByte, (Position*2)-2
    Function = TheByte AND &H03
End Function

Based upon position, this will move the two bits you want
to bits 0,1 .. then mask off the remaining bits.

Mike


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[Bern Ertl]

Andrew, SHIFT is a statement (SUB). You will need to create a function
to use it (BTW, Peter is right, convert to LONGS if possible).

'Added BYVAL so I can modify the parameters
Private Function Extract_TWO_Bits(BYVAL TheBYTE As Byte, BYVAL Position As Integer) As Integer

   'Assumes Position = 0,2,4,6
   SHIFT RIGHT TheBYTE, Position
   FUNCTION = TheBYTE AND &H03

END FUNCTION

Hey Mike! We posted at the same time!


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Bernard Ertl

[This message has been edited by Bern Ertl (edited March 21, 2001).]

[Andrew Peskin]

I want to say thank you for all of your comments and suggestions. They have all been very helpful.

Andrew

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[Semen Matusovski]

Inline assembler works much faster

#Compile Exe
#Dim All

Function PbMain
   Dim t1 As Single, t2 As Single, i As Long
   Dim Extract_TWO_Bits As Byte, TheBYTE As Byte, Position As Byte
   TheBYTE = 121
   Position = 4
   
   t1 = Timer
   For i = 1 To 10000000
     
     If Position = 0 Then Extract_TWO_Bits = (TheBYTE And 3) Else _
     If Position = 2 Then Extract_TWO_Bits = (TheBYTE And 12) \ 4  Else _
     If Position = 4 Then Extract_TWO_Bits = (TheBYTE And 48) \ 16 Else _
        Extract_TWO_Bits = TheBYTE \ 64
   Next

   t2 = Timer
   MsgBox Format$(1000 * (t2 - t1), "# ms"), , Str$(Extract_TWO_Bits)

   t1 = Timer
   For i = 1 To 10000000
      ! MOV AL, TheByte
      ! MOV CL, Position
      ! SHR AL, CL
      ! AND AL, 3
      ! MOV Extract_TWO_Bits, AL
   Next

   t2 = Timer
   MsgBox Format$(1000 * (t2 - t1), "# ms"), , Str$(Extract_TWO_Bits)

   t1 = Timer
   For i = 1 To 10000000
       Extract_TWO_Bits = TheByte
       Shift Right Extract_TWO_Bits, Position
       Extract_TWO_Bits = Extract_TWO_Bits And &H03
   Next
   t2 = Timer
   MsgBox Format$(1000 * (t2 - t1), "# ms"), , Str$(Extract_TWO_Bits)

End Function

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[Andrew Peskin]

How would you write the Assembeler to go Backwards, mimicking the following function:

Private Sub Set_TWO_Bits(TheBYTE As Byte, BitsTOSet As Integer, Position As Integer)
' This routine takes a Byte and then sets 2 of its bits to the value
'specified in "BitsTOSet".  It sets the bits located in the byte
'begining at the position specified by the "Position" parameter

   Select Case Position
    
     Case 0     '// Sets BITS 0 and 1 to the value of BitsTOSet
     TheBYTE = TheBYTE Or BitsTOSet
        
     Case 2     '// Sets BITS 2 and 3 to the value of BitsTOSet
     TheBYTE = TheBYTE Or (BitsTOSet * 4)
        
     Case 4     '// Sets BITS 4 and 5 to the value of BitsTOSet
     TheBYTE = TheBYTE Or (BitsTOSet * 16)
        
     Case 6     '// Sets BITS 6 and 7 to the value of BitsTOSet
     TheBYTE = TheBYTE Or (BitsTOSet * 64)
        
   End Select

Originally posted by Semen Matusovski:
Inline assembler works much faster

#Compile Exe
#Dim All

Function PbMain
   Dim t1 As Single, t2 As Single, i As Long
   Dim Extract_TWO_Bits As Byte, TheBYTE As Byte, Position As Byte
   TheBYTE = 121
   Position = 4
   
   t1 = Timer
   For i = 1 To 10000000
     
     If Position = 0 Then Extract_TWO_Bits = (TheBYTE And 3) Else _
     If Position = 2 Then Extract_TWO_Bits = (TheBYTE And 12) \ 4  Else _
     If Position = 4 Then Extract_TWO_Bits = (TheBYTE And 48) \ 16 Else _
        Extract_TWO_Bits = TheBYTE \ 64
   Next

   t2 = Timer
   MsgBox Format$(1000 * (t2 - t1), "# ms"), , Str$(Extract_TWO_Bits)

   t1 = Timer
   For i = 1 To 10000000
      ! MOV AL, TheByte
      ! MOV CL, Position
      ! SHR AL, CL
      ! AND AL, 3
      ! MOV Extract_TWO_Bits, AL
   Next

   t2 = Timer
   MsgBox Format$(1000 * (t2 - t1), "# ms"), , Str$(Extract_TWO_Bits)

   t1 = Timer
   For i = 1 To 10000000
       Extract_TWO_Bits = TheByte
       Shift Right Extract_TWO_Bits, Position
       Extract_TWO_Bits = Extract_TWO_Bits And &H03
   Next
   t2 = Timer
   MsgBox Format$(1000 * (t2 - t1), "# ms"), , Str$(Extract_TWO_Bits)

End Function

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[Andrew Peskin]

To Bern and Mike, what if I wanted to go backwards: Like the following Code:

Private Sub Set_TWO_Bits(TheBYTE As Byte, BitsTOSet As Integer, Position As Integer)
' This routine takes a Byte and then sets 2 of its bits to the value
' specified in "BitsTOSet".  It sets the bits located in the byte
' beginning at the position specified by the "Position" parameter


    Select Case Position
    
        Case 0     '// Sets BITS 0 and 1 to the value of BitsTOSet
            TheBYTE = TheBYTE Or BitsTOSet
        
        Case 2     '// Sets BITS 2 and 3 to the value of BitsTOSet
            TheBYTE = TheBYTE Or (BitsTOSet * 4)
        
        Case 4     '// Sets BITS 4 and 5 to the value of BitsTOSet
            TheBYTE = TheBYTE Or (BitsTOSet * 16)
        
        Case 6     '// Sets BITS 6 and 7 to the value of BitsTOSet
            TheBYTE = TheBYTE Or (BitsTOSet * 64)
        
    End Select

End Sub

Is there a function which could be written using the SHIFT command which accomplishes the same objective as the above Sub, but in a more efficient and streamlined manner?

Thanks in Advance.

Best regards,

Andrew Peskin
[email protected]

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[Bern Ertl]

Semen, I like your ASM example. Can you help me translate to LONGS
instead of BYTES? I tried converting to EAX but got strange results.
I'm not sure what registers are safe to use:

'translate following lines to ASM
'Temp & Source are LONG
'     Temp = Source
'     SHIFT RIGHT Temp, 6
'     INCR Temp

'Following does not work, AL is a BYTE or WORD?
      ! MOV AL, Source
      ! SHR AL, 6
      ! INC AL
      ! MOV Temp, AL

Andrew,

Depending on the situation in your code, you might either use

BIT [RE]SET source, bit#

or use a mask for the bits instead of shifting. Ie.:

InverseMask = &HF3 'Used to clear bits 2&3 (0 base)
Mask =  &H04       'Set bit 2
temp = source AND InverseMask  'Clear bits of interest
temp = source OR Mask          'Set needed bits

------------------
Bernard Ertl

[Semen Matusovski]

Andrew --

#Compile Exe
#Dim All

Function PbMain
   Dim t1 As Single, t2 As Single, i As Long
   Dim Set_TWO_Bits As Byte, TheBYTE As Byte, BitsTOSet As Byte, Position As Byte

   TheBYTE = 1253
   BitsTOSet = 2
   Position = 4
   
   t1 = Timer
   For i = 1 To 10000000
     If Position = 0 Then Set_TWO_Bits = TheBYTE Or BitsTOSet Else _
     If Position = 2 Then Set_TWO_Bits = TheBYTE Or (BitsTOSet * 4)  Else _
     If Position = 4 Then Set_TWO_Bits = TheBYTE Or (BitsTOSet * 16) Else _
                          Set_TWO_Bits = TheBYTE Or (BitsTOSet * 64)
   Next
   t2 = Timer
   MsgBox Format$(1000 * (t2 - t1), "# ms"), , Str$(Set_TWO_Bits)
   t1 = Timer
   For i = 1 To 10000000
      ! MOV AL, BitsTOSet
      ! MOV CL, Position
      ! SHL AL, CL
      ! MOV AH, TheBYTE
      ! OR  AH, AL
      ! MOV Set_TWO_Bits, AH
   Next
   t2 = Timer
   MsgBox Format$(1000 * (t2 - t1), "# ms"), , Str$(Set_TWO_Bits)
 End Function

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[Andrew Peskin]

How would you Set Bits 0 & 1, or Bits 2 & 3, or Bits 4 & 5, or Bits 6 & 7 to a specific value?

Is there something similar to the other example you posted for extracting Bits?

Thanks.

Andrew

Originally posted by Bern Ertl:
Semen, I like your ASM example. Can you help me translate to LONGS
instead of BYTES? I tried converting to EAX but got strange results.
I'm not sure what registers are safe to use:

'translate following lines to ASM
'Temp & Source are LONG
'     Temp = Source
'     SHIFT RIGHT Temp, 6
'     INCR Temp

'Following does not work, AL is a BYTE or WORD?
      ! MOV AL, Source
      ! SHR AL, 6
      ! INC AL
      ! MOV Temp, AL

Andrew,

Depending on the situation in your code, you might either use

BIT [RE]SET source, bit#

or use a mask for the bits instead of shifting. Ie.:

InverseMask = &HF3 'Used to clear bits 2&3 (0 base)
Mask =  &H04       'Set bit 2
temp = source AND InverseMask  'Clear bits of interest
temp = source OR Mask          'Set needed bits

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[Semen Matusovski]

Probably, there is better variant, but this works also not bad.

#Compile Exe
#Dim All

Function PbMain
   Dim t1 As Single, t2 As Single, i As Long
   Dim Set_TWO_Bits As Byte, TheBYTE As Byte, Position As Byte, NewValue As Byte

   TheBYTE =  &B10110101
   NewValue = &B10
   Position = 4
 
   t1 = Timer
   For i = 1 To 10000000
      ! MOV AL, &B11
      ! MOV CL, Position
      ! SHL AL, CL
      
      ! MOV AH, TheByte
      ! MOV DL, AH
      ! AND AH, AL
      ! SUB DL, AH
      
      ! MOV AL, NewValue
      ! SHL AL, CL
      ! ADD DL, AL
      ! MOV Set_TWO_Bits, DL
   Next
   t2 = Timer
   MsgBox Format$(1000 * (t2 - t1), "# ms"), , Bin$(Set_TWO_Bits, 8)
 End Function

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[Semen Matusovski]

Bern -
If you work with Long
! MOV EAX, Source
! SHR EAX, 6
! INC EAX
! MOV Temp, EAX




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