On Sun, 2009-05-24 at 14:33 +0100, Nathan Rixham wrote:
> Afternoon all,
>
> This is a quick survey, think it would be useful to have the values of
> MAX_FLOAT for each platform, and indeed see if it does differ.
>
> to do this can you please run the following code (bc* required) and
> reply back with the output (and your platform / php version)
>
> code:
> <?php
>
> function getMaxFloat() {
> $value = '1';
> $multiplier = '1';
> while(1) {
> $value = bcadd( $value , $multiplier );
> if( (float)$value == INF ) {
> $value = $oldvalue;
> $multiplier = '1';
> } elseif( ((float)bcadd( $value , '10' )) == INF ) {
> while(1) {
> $value = bcadd( $value , '1' );
> if( (float)$value == INF ) {
> return $oldvalue;
> }
> $oldvalue = $value;
> }
> }
> $oldvalue = $value;
> $multiplier = bcmul( $multiplier , '10' );
> }
> }
>
> define( 'FLOAT_MAX' , getMaxFloat() );
>
> echo FLOAT_MAX . PHP_EOL;
>
> ?>
>
> my results:
>
> Win Vista 32 bit on Intel Quad Core Duo - PHP 5.2.8
> 179769313486231580793728971405303415079934132710037826936173778980444968292764750946649017977587207096330286416692887910946555547851940402630657488671505820681908902000708383676273854845817711531764475730270069855571366959622842914819860834936475292719074168444365510704342711559699508093042880177904174497791
>
> Thanks!
Here's a faster version that takes a split second to evaluate:
<?php
function getMaxFloat()
{
$val1 = 2;
$val2 = 2;
for( ; ; )
{
$val2 = bcmul( $val1, $val1, 0 );
if( (string)((float)$val2) === 'INF' )
{
break;
}
$val1 = $val2;
}
for( ; ; )
{
$val2 = bcadd( $val1, $val1, 0 );
if( (string)((float)$val2) === 'INF' )
{
break;
}
$val1 = $val2;
}
$mod = bcdiv( $val1, 2, 0 );
for( ; ; )
{
if( (float)$mod < 1 )
{
break;
}
$val2 = bcadd( $val1, $mod, 0 );
if( (string)((float)$val2) === 'INF' )
{
$mod = bcdiv( $mod, 2, 0 );
}
else
{
$val1 = $val2;
}
}
return $val1;
}
define( 'FLOAT_MAX' , getMaxFloat() );
echo FLOAT_MAX . PHP_EOL;
?>
Also, when I tried using your INF comparison it always evaluated to
false so I did conversions to string... it's strange though since the
INF constant displayed "INF" when echoed and the (float)$val2 displayed
INF when echoed (when it passed the available limits) but comparing them
yielded false. Anyways:
AMD Phenom(tm) 9850 Quad-Core Processor
PHP 5.2.9
Ubuntu 8.04.2 (Hardy)
179769313486231580793728971405303415079934132710037826936173778980444968292764750946649017977587207096330286416692887910946555547851940402630657488671505820681908902000708383676273854845817711531764475730270069855571366959622842914819860834936475292719074168444365510704342711559699508093042880177904174497791
This is a match to your results.
Cheers,
Rob.
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