Talk:Efficiency Tester

The Elusive Run-Time of Hex

I'm next trying runs of the following instance of an llGetTime Efficiency Tester. You see five source lines commented out near the string "test once or more" ... I'm measuring the near zero cost of running with all five commented out, the max cost of none of the five commented out, and the individual costs of commenting in one line at a time ... We'll see if those results make sense, when they eventually appear. -- Ppaatt Lynagh 10:57, 27 October 2007 (PDT)

// Race a few versions of code.
// http://wiki.secondlife.com/wiki/hex

string XDIGITS1 = "0123456789abcdef"; // could be "0123456789ABCDEF"

string hexes1(integer bits)
{
    string nybbles = "";
    while (bits)
    {
        integer lsn = bits & 0xF; // least significant nybble
        string nybble = llGetSubString(XDIGITS1, lsn, lsn);
        nybbles = nybble + nybbles;
        bits = bits >> 4; // discard the least significant bits at right
        bits = bits & 0xfffFFFF; // discard the sign bits at left
    }
    return nybbles;
}

string hex1(integer value)
{
    if (value < 0)
    {
        return "-0x" + hexes1(-value);
    }
    else if (value == 0)
    {
        return "0x0"; // hexes(value) == "" when (value == 0)
    }
    else // if (0 < value)
    {
        return "0x" + hexes1(value);
    }
}

// http://wiki.secondlife.com/wiki/hex

string hex2(integer value)
{
    string lead = "0x";
    if (value & 0x80000000) // means (integer < 0) but is smaller and faster
    {
        lead = "-0x";
        value = -value; // unnecessary when value == -0x80000000
    }

    string nybbles = "";
    do
    {
        integer lsn = value & 0xF; // least significant nybble
        nybbles = llGetSubString("0123456789abcdef", lsn, lsn) + nybbles;
    } while ((value = (0xfffFFFF & (value >> 4))));

    return lead + nybbles;
}

string hex3(integer value)
{
    string lead = "0x";
    if (value & 0x80000000) // means (integer < 0) but is smaller and faster
    {
        lead = "-0x";
        value = -value; // unnecessary when value == -0x80000000
    }

    integer lsn; // least significant nybble
    string nybbles = "";
    do
    {
        nybbles = llGetSubString("0123456789abcdef", lsn = (value & 0xF), lsn) + nybbles;
    }
    while ((value = (0xfffFFFF & (value >> 4))));
    
    return lead + nybbles;
}

// http://wiki.secondlife.com/wiki/hex

string bits2nybbles4(integer bits)
{
    string nybbles = "";
    do
    {
        integer lsn = bits & 0xF; // least significant nybble
        nybbles = llGetSubString("0123456789ABCDEF", lsn, lsn) + nybbles;
    } while (bits = (0xfffFFFF & (bits >> 4)));
    return nybbles;
}

// http://wiki.secondlife.com/wiki/Talk:hex

string bits2nybbles5(integer bits)
{
    integer lsn; // least significant nybble
    string nybbles = "";
    do
    {
        integer lsn = bits & 0xF; // least significant nybble
        nybbles = llGetSubString("0123456789ABCDEF", lsn = (bits & 0xF), lsn) + nybbles;
    } while (bits = (0xfffFFFF & (bits >> 4)));
    return nybbles;
}

// IMPORTANT:
// Only perform tests in an empty region.
// To reduce contamination and be sure to wearing no attachments.
// Preferably do tests in a private sim with one on it.
// Don't move while performing the test.
// There is a margin of error so run the tests multiple times to determine it.

// (16384 - (15267 - 18)) was the well-known byte code size of this llGetTime/ llGetTimestamp harness

// Measure the race instead
// in calendar milliseconds elapsed since the day began,
// if called in place of llGetTime.

integer getTime() // count milliseconds since the day began
{
    string stamp = llGetTimestamp(); // "YYYY-MM-DDThh:mm:ss.ff..fZ"
    return (integer) llGetSubString(stamp, 11, 12) * 3600000 + // hh
           (integer) llGetSubString(stamp, 14, 15) * 60000 +  // mm
           llRound((float)llGetSubString(stamp, 17, -2) * 1000000.0)/1000; // ss.ff..f
}

default
{
    state_entry()
    {

        // always measure how small, not only how fast

        llOwnerSay((string) llGetFreeMemory() + " free bytes of code at default.state_entry");

        // always take more than one measurement

        integer repeateds;
        for (repeateds = 0; repeateds < 3; ++repeateds)
        {

            // declare test variables

            float counter;

            // declare framework variables

            float i = 0;
            float j = 0;
            integer max = 10000; // 2ms of work takes 20 seconds to repeat 10,000 times, plus overhead

            // begin

            float t0 = llGetTime();

            // loop to measure elapsed time to run sample code

            do
            {

              // test once or more
// hex1(0x7fffFFFF);
// hex2(0x7fffFFFF);
// hex3(0x7fffFFFF);
// bits2nybbles4(0x7fffFFFF);
// bits2nybbles5(0x7fffFFFF);
      
            } while (++i < max);

            float t1 = llGetTime();

            // loop to measure elapsed time to run no code

            do ; while (++j < max);

            float t2 = llGetTime();

            // complain if time ran backwards
            
            if (!((t0 <= t1) && (t1 <= t2)))
            {
                llOwnerSay("MEANINGLESS RESULT -- SIMULATED TIME RAN BACKWARDS -- TRY AGAIN");
            }
            
            // report average time elapsed per run

            float elapsedms = 1000.0 * (((t1 - t0) - (t2 - t1)) / max);
            llOwnerSay((string) elapsedms + "+-??% ms may have elapsed on average in each of");
            llOwnerSay((string) max + " trials of running the code in the loop");
        }
    }
}