On 10/11/07, tedd <tedd@xxxxxxxxxxxx> wrote:
>
> At 4:18 PM -0600 10/10/07, <admin@xxxxxxxxxxxxxxxxxxx> wrote:
> >I disagree. I will need to see an example where the round() is
> inaccurate.
>
>
> You may disagree if you wish, but the php function round() is
> inaccurate by definition -- all *rounding* algorithms are inaccurate.
>
thats why i suggested the bcmath based algorithm, as bcmath supports
arbitrary
precision. i built a quick test script using the method from the top
comment of the
bcmath page, and round(). it allows for quick comparisons of the 2
algorithms and
tells you if the results are the same. i messed around w/ it a little bit
and the results
were the same every time.
nathan@devel ~/working/www $ vim bcRound.php
nathan@devel ~/working/www $ ./bcRound.php 5.58635634564356 6
round result: 5.586356
roundbc result: 5.586356
the results are different
nathan@devel ~/working/www $ vim bcRound.php
nathan@devel ~/working/www $ ./bcRound.php 5.58635634564356 6
round result: 5.586356
roundbc result: 5.586356
the results are the same
nathan@devel ~/working/www $ ./bcRound.php 5.58635634564356 8
round result: 5.58635635
roundbc result: 5.58635635
the results are the same
nathan@devel ~/working/www $ ./bcRound.php 5.58635634564356 3
round result: 5.586
roundbc result: 5.586
the results are the same
i dont know what the point of the toFixed() function is (posted earlier).
round takes a second parameter that specifies the desired precision.
#!/usr/bin/php
<?php
if($argc != 3) {
die('Usage: rounder.php <float> <precision>' . PHP_EOL);
}
$float = $argv[1];
$precision = $argv[2];
$roundResult = round($float, $precision);
$roundbcResult = roundbc($float, $precision);
echo "round result: $roundResult" . PHP_EOL;
echo "roundbc result: $roundbcResult" . PHP_EOL;
if($roundResult !== $roundbcResult) {
echo 'the results are the same' . PHP_EOL;
} else {
echo 'the results are different' . PHP_EOL;
}
/// borrowed from post on php.net
function roundbc($x, $p) {
$x = trim($x);
$data = explode(".",$x);
if(substr($data[1],$p,1) >= "5") {
//generate the add string.
$i=0;
$addString = "5";
while($i < $p) {
$addString = "0" . $addString;
$i++;
}//end while.
$addString = "." . $addString;
//now add the addString to the original fraction.
$sum = bcadd($data[0] . "." . $data [1],$addString,$p+1);
//explode the result.
$sumData = explode(".",$sum);
//now, return the correct precision on the rounded number.
return $sumData[0] . "." . substr($sumData[1],0,$p);
} else {
//don't round the value and return the orignal to the desired
//precision or less.
return $data[0] . "." . substr($data[1],0,$p);
}//end if/else.
}//end roundbc.
?>
-nathan
