.I am trying to correct some PHP code to calculate probability of generating a block for bitbot. bd_ and llama have provided some debate regarding how to calculate it and I suggest it be moved to forum for further eyes to analyze their findings and to come to a conclusion on best formula to calculate probability.

For now, here's code I've been using:

//var p = target*rate*1000/Math.pow(2,256);

//var txt = "<table border='1'>

// <tr style='font-weight:bold'> <td>Probability</td> <td>Time</td></tr>\n"+"

// <tr> <td>Average</td> <td>"+getHumanTime(1/p)+"</td></tr>\n"+getRow(0.50,p)+getRow(0.95,p)+"</table>";

//document.getElementById('answer').innerHTML = txt;

//function getRow(prob,p) { return "<tr><td>"+100*prob+"%</td><td>"+getHumanTime(-Math.log(1-prob)/p)+"</td></tr>\n";

bcscale(256);

$a = bcsub(bcpow(2,256),1);

$b = bcmul(bcpow(2,32),$difficulty);

$target = bcdiv($a,$b); // target

$pph = bcdiv($target,bcpow(2,256)); // probability per hash

if (isset($_GET["r"]) && $_GET["r"] != "") {

$rate = $_GET["r"];

if (is_numeric($rate)) {

function humantime($secs) {

if ($secs<0) return false;

$m = (int)($secs / 60); $s = $secs % 60; $s = ($s <= 9) ? "0$s" : $s;

$h = (int)($m / 60); $m = $m % 60; $m = ($m <= 9) ? "0$m" : $m;

$d = (int)($h / 24); $h = $h % 24;

return $d."d $h:$m:$s";

}

echo "http://bitcointalk.org/index.php?topic=471.0";exit;

// Where does this go?

// <bd_> To compute the number of hashes needed to reach a success probability of P_targ, you'll want n >= log(P_targ)/log(1-P)

// <bd_> So time needed is (log(P_targ)/log(1-P))/rate

// <bd_> To compute the probability per second, you'll want 1-(1-p)^rate, where p is the probability of a single hash being correct

//$pps = bcdiv(bcmul($target,1000),bcpow(2,256)); // probability per second (according to bd_ this is wrong)

bcscale(16); // Next calculation takes too long for higher bits

$pps = bcsub(1,bcpow(bcsub(1,$pph),$rate)); // probability per second

//echo "probabiliy per second == 1-(1-p)^rate == 1-(1-$pph)^$rate == $pps";exit;

// Comment next line for 256-bits of data

bcscale(16);

$ppr = bcmul($pps,$rate);

//$ppr = $pps;

$etaAvg = humantime(bcdiv(1,$ppr));

$eta25 = humantime(bcdiv(-log(.75),$ppr));

$eta50 = humantime(bcdiv(-log(.5),$ppr));

$eta75 = humantime(bcdiv(-log(.25),$ppr));

$eta95 = humantime(bcdiv(-log(.05),$ppr));

$eta99 = humantime(bcdiv(-log(.01),$ppr));

echo "ProbabilityPerSecond($ppr) Avg($etaAvg) 25%($eta25) 50%($eta50) 75%($eta75) 95%($eta95) 99%($eta99)";

} else echo "This command requires either no argument or a numeric argument representing khash/sec.";

}

else {

bcscale(32);

$pph = bcmul($pph,1);

echo "ProbabilityPerHash($pph)";

}

http://nullvoid.org/bitcoin/bc.php?q=gethashprobability&r=2000 where r is your khash/sec