floor

add a note User Contributed Notes

Jared Fine
30-May-2006 11:16


Due to the floating point precision issue (http://www.php.net/float) if you round() one additional decimal point prior to calling floor() you will get the expected result.



For example:

echo floor((0.1 + 0.7) * 10); // echo's 7

echo floor(round((0.1 + 0.7) * 10, 1)); // echo's 8

Andreas Blixt
28-May-2006 04:26


Simpler version of Bruteork's example (though not making use of floor()):

<?php

if ($counter % 2 == 0) echo "even";

?>

peter at harbour-design dot co dot uk
25-Jan-2005 05:52


If you are after just removing the decimal places and returning an integer, try:



<?

$iPosDecimalNo = 5.67;

$iNegDecimalNo = -5.67;



print (int)$iPosDecimalNo;

print (int)$iNegDecimalNo;

?>



result will:



5

-5



No rounding up or down, just truncation and works for positive and negative numbers.

sam at bigroomstudios dot com
31-Aug-2004 11:59


Here's a way to get around jolyon's 79.99 problem (below).  If you want to take a float value representing a price and drop off any fractions of a cent, use this:



<?php



function round_to_penny($amount){

    

    $string = (string)($amount * 100);



    $string_array = split("\.", $string);

    

    $int = (int)$string_array[0];

    

    $return = $int / 100;

    

    return $return;



}



print( round_to_penny(79.99999) ); //result: 79.99



?>



Probably not super efficient, but get's the job done if you've already invested in using float values.



Cheers,

Sam

jolyon at mways dot co dot uk
11-Aug-2004 12:41


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:



<?

$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 :)

illyena at musefish dot net
13-May-2004 06:53


For calculating the number of days, hours, minutes and seconds to an event.



<?

$then = date(mktime(8,0,0,6,25,2004)); //remember that mktime is hour,min,sec,month,day,year

$now = date("U"); // "U" is the number of seconds since the epoch, equivilant to using "YmdHis"



$time = $then - $now; //gets the number of seconds between now and the event

$days = floor($time/86400); //rounds down to the whole number, in this case # of days

echo $days." Days";

$time = $time - ($days*86400); //leaves you with the amount of time ramaining after subtracting the days

$hours = floor($time/3600); //rounds down to the whole number, in this case # of hours

echo $hours." Hours";

$time = $time - ($hours*3600); //leaves you with the amount of time ramaining after subtracting the hours

$min = floor($time/60); //rounds down to the whole number, in this case # of minutes

echo $min." Minutes";

$sec = $time - ($min*60); //leaves you with the amount of time ramaining after subtracting the minutes which is equivilant to the remainins seconds

echo $sec." Seconds";

?>

twindagger2k3 at NOSPAMyahoo dot com
14-Feb-2004 07:58


In response to PHP Helper, the floor function does strip the decimal part if the number is positive. However, if the number is negative, it will not. for example:



<?php



$test = 5.6;

echo floor($test); //5



$test = -5.6;

echo floor($test); //-6



?>



The rounding mentioned in PHP Helper's post will work for both positive and negative numbers.

PHP Helper
20-Dec-2003 06:39


floor basically truncates, or chops off everything to the right of a decimal. For instance, if you have a length of 5.1234, but just wanted the whole number, you could use the following code:



<?php

$length = 5.1234; //this is our original length

$length = floor($length); //length is truncated, original variable name is kept

print "$length"; //this prints our result

?>



This code would print the following: 5



Now, although there is a specific function in PHP for rounding, rounding can also be performed with the floor function. Let's say we wanted to round the length to the hundredths place.



<?php

$length = 5.1234;

$length = floor(($length) * 100 + .5) * .01;

print "$length";

?>



The result is: 5.12



This works because, first, the length is multiplied by 100, which moves the decimal point to the right two places, giving us the value of 512.34. Next .5 is added to the length, which gives us a value of 512.84. Then the floor function truncates the value, leaving us with 512. Lastly, to compensate for multiplying by 100 earlier, now we must divide by 100, or in this case, multiply by .01. This moves the decimal point back 2 places to it's original place and gives us the rounded value of 5.12.



We can also round to other values, such as the thousandths, by adjusting the code as follows:



<?php

$length = 5.1234;

$length = floor(($length) * 1000 + .5) * .001;

print "$length";

?>



Result: 5.123

asp55 at digiclub dot org
15-Feb-2003 06:52


Just a quick example of how to use this method



The first is just used to determine whether a number is even or odd:



<? 

if(($x - (2 * floor($x/2))) == 0) echo "even";

else echo "odd";

?>



The second is just to determine a persons age by comparing their birthday with the current date and rounding down:



<? $age = floor((date(Ymd) - $bday)/10000); ?>

10-Sep-2002 06:08


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:



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!):



$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(), ...

thouartjay at hotmail dot com
24-Jun-2002 09:37


In response to netben's comment, another conversion for a string is:



$myStr = "29.01";

$myStr = (float) $myStr;



In all, any string (as used as in this example) will be treated as float, and no conversion necessary.

alhall at jcw dot org
28-Feb-2002 01:17


//Using floor() to round decimals.

$original_price=12.72

$discount=$original_price*.40;

  $discount=floor(($discount * 100)+.5)/100;

//$discount=5.088

//$discount after floor() = 5.09

mail at sebastian-bopp dot de
07-Feb-2002 12:37


Note:



echo floor(1.6); // will output "1"

echo floor(-1.6); // will output "-2"

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