floor
(PHP 4, PHP 5)
floor — Округляет дробь в меньшую сторону
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Коментарии
mathematical functions lack a floating point version of the modulo operation, which returns the difference between the floor() of the argument and the argument itself:
<?php
function fmod($value) {
return $value - floor($value);
}
?>
Very useful with trigonometric functions to reduce the angle argument to a circle that includes angle 0.
Useful also to reduce an arbitrarily large floating point value into an entropy source, by first transforming this value into a pair using logarithm functions with distinct bases (add 1 if the function can return 0, to avoid floating point errors with logarithms!):
<?php
$f = 1 + @disk_free_space("/tmp");
$r = (int)(fmod(Log($f)) * 0x7FFFFFFF)
^ (int)(fmod(Log10($f)) * 0x7FFFFFFF)
?>
Then $r can be used as a good entropy source, if the free space in your temporary folder used by PHP is constantly evolving within a large range of values.
You can combine this value by xoring it with other values such as time(), (int)microtime(), ip2long($_SERVER['REMOTE_ADDR'], $_SERVER['REMOTE_PORT'], getmypid(), ...
Beware of FLOAT weirdness!
Floats have a mind of their own, and what may look like an integer stored in a float isn't.
Here's a baffling example of how floor can be tripped up by this:
<?php
$price = 79.99;
print $price."\r\n"; // correct result, 79.99 shown
$price = $price * 100;
print $price."\r\n"; // correct result, 7999 shown
print floor($price); // 7998 shown! what's going on?
?>
The thing to remember here is that the way a float stores a value makes it very easy for these kind of things to happen. When the 79.99 was multiplied by 100, the actual value stored in the float was probably something like 7998.9999999999999999999999999999999999, PHP would print out 7999 when the value is displayed but floor would therefore round this down to 7998.
THe moral of this story - never use float for anything that needs to be accurate! If you're doing prices for products or a shopping cart, then always use an integer and store prices as a number of pence, you'll thank me for this later :)
<?php
echo floor(1.6); // will output "1"
echo floor(-1.6); // will output "-2"
?>
instead use intval (seems to work v5.1.6):
<?php
echo intval(1.6); // will output "1"
echo intval(-1.6); // will output "-1"
?>
Note:
<?php
$int = 0.99999999999999999;
echo floor($int); // returns 1
?>
and
<?php
$int = 0.9999999999999999;
echo floor($int); // returns 0
?>
I believe this behavior of the floor function was intended. Note that it says "the next lowest integer". -1 is "higher" than -1.6. As in, -1 is logically greater than -1.6. To go lower the floor function would go to -2 which is logically less than -1.6.
Floor isn't trying to give you the number closest to zero, it's giving you the lowest bounding integer of a float.
In reply to Glen who commented:
Glen
01-Dec-2007 04:22
<?php
echo floor(1.6); // will output "1"
echo floor(-1.6); // will output "-2"
?>
instead use intval (seems to work v5.1.6):
<?php
echo intval(1.6); // will output "1"
echo intval(-1.6); // will output "-1"
?>
But, if you want the number closest to zero, you could use this:
<?php
if($foo > 0) {
floor($foo);
} else {
ceil($foo);
}
?>
-benrr101
Have solved a "price problem":
<?php
$peny = floor($row->price*1000) - floor($row->price)*1000)/10;
?>
If you're wanting to round down to the nearest hundred:
<?php
function rounddowntohundred($theNumber) {
if (strlen($theNumber)<3) {
$theNumber=$theNumber;
} else {
$theNumber=substr($theNumber, 0, strlen($theNumber)-2) . "00";
}
return $theNumber;
}
?>
I use this function to floor with decimals:
<?php
function floordec($zahl,$decimals=2){
return floor($zahl*pow(10,$decimals))/pow(10,$decimals);
}
?>
A correction to the funcion floor_dec from the user "php is the best".
If the number is 0.05999 it returns 0.59 because the zero at left position is deleted.
I just added a '1' and after the floor or ceil call remove with a substr.
Hope it helps.
function floor_dec($number,$precision = 2,$separator = '.') {
$numberpart=explode($separator,$number);
$numberpart[1]=substr_replace($numberpart[1],$separator,$precision,0);
if($numberpart[0]>=0) {
$numberpart[1]=substr(floor('1'.$numberpart[1]),1);
} else {
$numberpart[1]=substr(ceil('1'.$numberpart[1]),1);
}
$ceil_number= array($numberpart[0],$numberpart[1]);
return implode($separator,$ceil_number);
}
Warning: do not use Seppili's function to floor with decimals. It will lead you to a lot of trouble because of float number precision.
For example floordec(0.29, 2) will result in 0.28.
Here's a little fix that will help you get around some problems:
<?php
function floordec($value,$decimals=2){
return floor($value*pow(10,$decimals)+0.5)/pow(10,$decimals);
}
?>
<?php
echo (2.3 * 100) . ' - ' . round(2.3 * 100, 0) . ' - ' . floor(2.3 * 100);
?>.
Result:
230 - 230 - 229
Be careful!