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Fast hex conversion (followup)

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  • Fast hex conversion (followup)

    I made two other optimizations to Dave Roberts' code here: http://www.powerbasic.com/support/pb...388#post280388, and lately I've been using Dave's timer a lot too (hey, I added one or two lines of code in there, just pull out a magnifying glass and you'll find them)

    Code:
    #COMPILE EXE
    #DIM ALL
    DECLARE FUNCTION QueryPerformanceCounter LIB "KERNEL32.DLL" ALIAS "QueryPerformanceCounter" (lpPerformanceCount AS QUAD) AS LONG
    DECLARE FUNCTION QueryPerformanceFrequency LIB "KERNEL32.DLL" ALIAS "QueryPerformanceFrequency" (lpFrequency AS QUAD) AS LONG
    
    '~~~~~~~~~~~A Variation of Dave Roberts' MACRO Timer~~~~~~~~~~~~~~~~~~~~~~~
    MACRO onTimer
      LOCAL qFreq, qOverhead, qStart, qStop AS QUAD
      LOCAL f AS STRING
      f = "#.###"
      QueryPerformanceFrequency qFreq
      QueryPerformanceCounter qStart ' Intel suggestion. First use may be suspect
      QueryPerformanceCounter qStart ' So, wack it twice <smile>
      QueryPerformanceCounter qStop
      qOverhead = qStop - qStart     ' Relatively small
    END MACRO
    
    MACRO goTimer = QueryPerformanceCounter qStart
    MACRO stopTimer = QueryPerformanceCounter qStop
    
    MACRO showTimer = USING$(f,(qStop - qStart - qOverhead)*1000000/qFreq /1000) + " milliseconds"
    '~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    
    FUNCTION PBMAIN () AS LONG
    
      DIM hashByte() AS BYTE
      DIM hashByteHex () AS STRING * 2
      DIM hashByteHexW () AS WORD       'use fast intrinsic WORD type rather than STRING * 2
      DIM hexArr(255) AS WORD
      LOCAL hashText AS STRING
      LOCAL hashSize, i AS LONG
    
      hashSize = 3200000 ' bytes for example
      
      FOR i = 0 TO 255                  'pre-calculate the hex translation array to avoid the HEX$() conversion later
         hexArr(i) = CVWRD(HEX$(i, 2))
      NEXT
    
      REDIM hashByte(hashSize -1) AS BYTE
    
      FOR i = 0 TO hashSize- 1
        hashByte(i) = RND(0,255) ' Output from a hashing algorithm, for example
      NEXT
    
      hashText = SPACE$(2*hashSize)
      REDIM hashByteHex( hashSize - 1)  AS STRING * 2 AT STRPTR(hashText)
      REDIM hashByteHexW( hashSize - 1) AS WORD       AT STRPTR(hashText)
    
      onTimer
      goTimer
      FOR i = 0 TO hashSize-1
        hashByteHex(i) =   HEX$( hashByte( i ),2 )   'comment each line out in turn to compare speed
    '   hashByteHexW(i) = hexArr( hashByte( i )   )  'comment each line out in turn to compare speed
      NEXT
      stopTimer
    
      MSGBOX showTimer & $CRLF & $CRLF & RIGHT$(hashText, 2000)
    
    END FUNCTION
    Last edited by John Gleason; 29 Mar 2008, 09:15 AM. Reason: noted variation of timer macro from Dave's code

  • #2
    Mind boggling.

    Of course, the Hex$ conversion is not being avoided.

    You are effectively creating a look-up table and its creation overhead is more than offset by HEX$(i, 2) being faster to read than HEX$( hashByte( i ),2 ) or, more to the point, reading 'i' is faster than reading 'hashByte( i )'.

    Your code illustrates the use of some of the PowerBASIC commands which we all read on getting the compiler manual and wonder what on earth they'd be used for and then promptly forget they exist. It is probably worthwhile for a lot of us to sit down quietly sometime and browse through the commands again. No doubt some of us will find ourselves saying "That didn't make much sense the first time that I read that but, Oh boy, do I have a use for it now."

    I'm not keen on your alterations to my timer macro.

    I may be nitpicking but 'Dave Roberts' MACRO Timer' should read 'A variation of Dave Roberts' MACRO Timer'.

    OnTimer suggests to me that maybe an OffTimer exists and some tidying up is required. My InitializeTimer is clearly a one off statement. Perhaps SetUpTimer would be a better term.

    As for the goTimer/stopTimer pair rather than my StartTimer/StopTimer pair I see that as traffic lights compared to a stopwatch. I'll stay withh the stopwatch.


    The '*1000000/qFreq /1000' is effectively the same as my '*1000/qFreq' with redundancy. I guess you were tweaking there and forgot to tidy up.

    I am now declaring qFreq, and so on, as Globals so that the associated macros may be used in functions.

    Comment


    • #3
      I'll update my post above to note the timer macro is a (slight) variation.
      As for the goTimer/stopTimer pair rather than my StartTimer/StopTimer
      I only changed the names because I use it so much I wanted them as short as possible and still make some sense.
      And the extra /1000 gives milli and microseconds without having to count thru any digits. My computer is only accurate to +- a few microsecs using the performanceCounter anyway, so that resolution is enough to cover it.

      Also, here is a hard-coded look-up table for to use instead of that much slower HEX$ loop:
      Code:
        ARRAY ASSIGN hexArr() = &h3030, _
           &h3130,&h3230,&h3330,&h3430,&h3530,&h3630,&h3730,&h3830,&h3930,&h4130,&h4230,&h4330,&h4430,&h4530,&h4630,&h3031, _
           &h3131,&h3231,&h3331,&h3431,&h3531,&h3631,&h3731,&h3831,&h3931,&h4131,&h4231,&h4331,&h4431,&h4531,&h4631,&h3032, _
           &h3132,&h3232,&h3332,&h3432,&h3532,&h3632,&h3732,&h3832,&h3932,&h4132,&h4232,&h4332,&h4432,&h4532,&h4632,&h3033, _
           &h3133,&h3233,&h3333,&h3433,&h3533,&h3633,&h3733,&h3833,&h3933,&h4133,&h4233,&h4333,&h4433,&h4533,&h4633,&h3034, _
           &h3134,&h3234,&h3334,&h3434,&h3534,&h3634,&h3734,&h3834,&h3934,&h4134,&h4234,&h4334,&h4434,&h4534,&h4634,&h3035, _
           &h3135,&h3235,&h3335,&h3435,&h3535,&h3635,&h3735,&h3835,&h3935,&h4135,&h4235,&h4335,&h4435,&h4535,&h4635,&h3036, _
           &h3136,&h3236,&h3336,&h3436,&h3536,&h3636,&h3736,&h3836,&h3936,&h4136,&h4236,&h4336,&h4436,&h4536,&h4636,&h3037, _
           &h3137,&h3237,&h3337,&h3437,&h3537,&h3637,&h3737,&h3837,&h3937,&h4137,&h4237,&h4337,&h4437,&h4537,&h4637,&h3038, _
           &h3138,&h3238,&h3338,&h3438,&h3538,&h3638,&h3738,&h3838,&h3938,&h4138,&h4238,&h4338,&h4438,&h4538,&h4638,&h3039, _
           &h3139,&h3239,&h3339,&h3439,&h3539,&h3639,&h3739,&h3839,&h3939,&h4139,&h4239,&h4339,&h4439,&h4539,&h4639,&h3041, _
           &h3141,&h3241,&h3341,&h3441,&h3541,&h3641,&h3741,&h3841,&h3941,&h4141,&h4241,&h4341,&h4441,&h4541,&h4641,&h3042, _
           &h3142,&h3242,&h3342,&h3442,&h3542,&h3642,&h3742,&h3842,&h3942,&h4142,&h4242,&h4342,&h4442,&h4542,&h4642,&h3043, _
           &h3143,&h3243,&h3343,&h3443,&h3543,&h3643,&h3743,&h3843,&h3943,&h4143,&h4243,&h4343,&h4443,&h4543,&h4643,&h3044, _
           &h3144,&h3244,&h3344,&h3444,&h3544,&h3644,&h3744,&h3844,&h3944,&h4144,&h4244,&h4344,&h4444,&h4544,&h4644,&h3045, _
           &h3145,&h3245,&h3345,&h3445,&h3545,&h3645,&h3745,&h3845,&h3945,&h4145,&h4245,&h4345,&h4445,&h4545,&h4645,&h3046, _
           &h3146,&h3246,&h3346,&h3446,&h3546,&h3646,&h3746,&h3846,&h3946,&h4146,&h4246,&h4346,&h4446,&h4546,&h4646

      Comment


      • #4
        Hex pairs==>bytes and bytes==>hex pairs

        http://www.powerbasic.com/support/pb...ad.php?t=25176

        Note not the same thing as reading/writing MKI$ or MKWRD$ strings but easily adaptable to same.

        Of course, you'd never read a string of MKI$ or MKWRD$ strings, you'd...
        Code:
        REDIM Foo(LEN(string)\2-1) AS INTEGER|WORD AT STRPTR(string)
        Last edited by Michael Mattias; 29 Mar 2008, 09:46 AM. Reason: Forgot to divide by SIZEOF(WORD)
        Michael Mattias
        Tal Systems (retired)
        Port Washington WI USA
        [email protected]
        http://www.talsystems.com

        Comment


        • #5
          I have just realised that Gary Barnes sneaked the 1000000 into the macro. My opening post used 1000.

          John, your code is now getting so close to light speed it is in serious danger of evaporating.

          Comment


          • #6
            The cameras are rolling and you are just about to put the flag up when someone chips in with "So, whose footprint is that then?". Oh, dear.

            Comment


            • #7
              I didn't sneak it in
              I wanted the result in micro seconds to measure how long the sleep instruction takes. I thought that it might be instructive to post it.
              I humbly seek your forgiveness David for sullying the purity of your post
              Gary Barnes
              The Control Key

              If you are not part of the solution
              then you are either a gas, solid, plasma or some other form of matter.

              Comment


              • #8
                I don't do purity, Gary. At my age I figured I should at least be able see it on the horizon. I think that is the best that I can hope for now.

                Comment


                • #9
                  I thought that it might be instructive
                  and indeed it was. For some reason, I used to think SLEEP had only like 50 milliSec resolution and never thought to test it. Now I know that except for maybe 1,2,3,4 which all seem to be around 3 or 4mSec, it is pretty much right on the millisecond.

                  Comment


                  • #10
                    Cheers David
                    Gary Barnes
                    The Control Key

                    If you are not part of the solution
                    then you are either a gas, solid, plasma or some other form of matter.

                    Comment


                    • #11
                      Before I forget, I've added 'Macro nTimeTaken = Val(TimeTaken)' to the macro so we could have, for example:

                      tot = tot + nTimeTaken

                      or Macro nshowTimer = Val(showTimer) in John's variant.

                      Comment

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