(PHP 4 >= 4.2.0, PHP 5, PHP 7)
is_infinite — 判断是否为无限值
$val
)
如果 val
为无穷大（正的或负的），例如 log(0)
的结果或者任何超出本平台的浮点数范围的值，则返回 TRUE。
val要检查的值
如果 val
为无穷大返回 TRUE，否则返回 FALSE。
fastest version to php <4.2:
<?php function is_infinite($v){$v=$v>>0;return -9e1000==$v||$v==9e1000;}; ?>
the $v=$v>>0; is just to ensure it is a number and its not mandatory.
effectively, the function can be reduced to:
<?php function is_infinite($v){return -9e1000==$v||$v==9e1000;}; ?>
this works because any number that is too big or too small for a float is considered to be infinite or -infinite.
PHP_INT_MAX is The largest integer supported in this build of PHP. Usually int(2147483647). Available since PHP 4.4.0 and PHP 5.0.5
Actually any string ending in INF is more appropriate than any string beginning with INF. Since negative infinity evaluates to "-INF" but it is still infinite. However in either case the STRING "INF" is not infinite, only a float that converts to "INF" or "-INF" is infinite.
A more appropriate function might be:
<?php
if (!is_defined('is_infinite')) { function is_infinite($val) {
return (is_float($val) and ("$val"=='INF' or "$val"=='-INF'));
} }
?>
* However the above function is untested.
@ david,
That will return true for any string ending with "INF".
I think substr("$value",0,3) would be more appropriate.
If you have PHP lower than 4.2 you can simulate the behaviour:
function is_infinite($value) {
return (substr("$value",-3) == "INF");
}
(tested on php 4.1.2)