fmod

(PHP 4 >= 4.2.0, PHP 5, PHP 7)

fmod — 返回除法的浮点数余数

说明

float fmod ( float $x , float $y )

返回被除数（x）除以除数（y）所得的浮点数余数。余数（r）的定义是：x = i * y + r，其中 i 是整数。如果 y 是非零值，则 r 和 x 的符号相同并且其数量值小于 y。

参数

x

被除数

y

除数

返回值

x/y的浮点数余数。

范例

Example #1 fmod() 的使用

<?php
$x = 5.7;
$y = 1.3;
$r = fmod($x, $y);
// $r equals 0.5, because 4 * 1.3 + 0.5 = 5.7
?>

User Contributed Notes

nospam at neonit dot de 04-Jan-2017 07:11
Note that fmod does not behave like a similar function written in PHP itself does due to the lack of fixing floating point representation errors.

Have a look at this:
<?php
var_dump(10 / (10 / 3) === 3.0); // bool(true)
var_dump(fmod(10, 10 / 3)); // float(3.3333333333333)
var_dump(fmod(10, 10 / 3) < 10 / 3); // bool(true)
?>

Internally there is no way of exactly representing the result of 10 / 3, so it will always be a bit above or below the actual result. In this case, the example proves it being a bit above the actual result.

PHP seems quite good at auto-fixing floating point representation errors so they behave like the user would expect it. That's why the first line yields true, although the result is slightly below 3 (like 2.9999999999[something]). I failed to trick PHP into rounding or cropping the result to 2.

However, fmod seems to not apply these fixes during calculations. From 10 / 3 it gets a value slightly below 3, floors it to 2 and returns 10 - 2 * 10 / 3, which is slightly less than the actual result of 10 / 3, but looks like 10 / 3 (third line).

Unfortunately, this is not the expected result. See other notes for high quality fixes.
timo underscore teichert at yahoo dot de 27-Oct-2014 10:40
The behaviour of this function seems to have changed over time.

<?php

echo fmod(3,5);
// php 5.3.2 outputs -2
// php 5.3.8 outputs 3

echo fmod(2,5);
// php 5.3.2 outputs 2
// php 5.3.8 outputs 2

?>

- Timo
KRAER 28-Jan-2014 08:23
To create a list of primes in a bash based on php wich can be resumed after breaking I did use fmod() and some snippets offered by two more users here on php comments.

This will output :
"prime;difference-between-last-and-current-prime"

So credit goes to them. I only did the logfile output.

This will function up to whatever fmod supports as highest value. Just enter the $end value. And do a touch to the logfile followed by chmod 666 so php can access it.

<?php
function tailCustom($filepath, $lines = 1, $adaptive = true) {
 
        // Open file
        $f = @fopen($filepath, "rb");
        if ($f === false) return false;
 
        // Sets buffer size
        if (!$adaptive) $buffer = 4096;
        else $buffer = ($lines < 2 ? 64 : ($lines < 10 ? 512 : 4096));
 
        // Jump to last character
        fseek($f, -1, SEEK_END);
 
        // Read it and adjust line number if necessary
        // (Otherwise the result would be wrong if file doesn't end with a blank line)
        if (fread($f, 1) != "\n") $lines -= 1;
       
        // Start reading
        $output = '';
        $chunk = '';
 
        // While we would like more
        while (ftell($f) > 0 && $lines >= 0) {
 
            // Figure out how far back we should jump
            $seek = min(ftell($f), $buffer);
 
            // Do the jump (backwards, relative to where we are)
            fseek($f, -$seek, SEEK_CUR);
 
            // Read a chunk and prepend it to our output
            $output = ($chunk = fread($f, $seek)) . $output;
 
            // Jump back to where we started reading
            fseek($f, -mb_strlen($chunk, '8bit'), SEEK_CUR);
 
            // Decrease our line counter
            $lines -= substr_count($chunk, "\n");
 
        }
 
        // While we have too many lines
        // (Because of buffer size we might have read too many)
        while ($lines++ < 0) {
 
            // Find first newline and remove all text before that
            $output = substr($output, strpos($output, "\n") + 1);
 
        }
 
        // Close file and return
        fclose($f);
        return trim($output);
 
    }

function isPrime( $num )
{
    for( $i = 2; $i*$i <= $num; $i++ )
        if( !fmod($num,$i) )
            return FALSE;

    return TRUE;
}

$logfile = 'prim_save.log';

$lastline = explode(";", tailCustom($logfile));
$begin = ($lastline[0] +1);
$lastprime = $lastline[0];

$end = 999999999999999999999999999999999999;

$fp = fopen($logfile, 'a');
//Lineformat    $i.';'.$difference.';'."\n"

for($i = $begin; $i<$end; $i++)
{
    if(isPrime($i) == TRUE)
    {
        $difference = $i - $lastprime;
        fputs($fp,$i.';'.$difference.';'."\n");
        $lastprime = $i;
    }
}

fclose($fp);
?>
Adrien Gibrat 06-Jul-2013 07:33
There is an elegant way to do compute gcm :
https://en.wikipedia.org/wiki/Greatest_common_divisor

    // Recursive function to compute gcd (euclidian method)
    function gcd ($a, $b) {
        return $b ? gcd($b, $a % $b) : $a;
    }
    // Then reduce any list of integer
    echo array_reduce(array(42, 56, 28), 'gcd'); // === 14

If you want to work with floating points, use approximation :

    function fgcd ($a, $b) {
        return $b > .01 ? fgcd($b, fmod($a, $b)) : $a; // using fmod
    }
    echo array_reduce(array(2.468, 3.7, 6.1699), 'fgcd'); // ~= 1.232

You can use a closure in PHP 5.3 :

    $gcd = function ($a, $b) use (&$gcd) { return $b ? $gcd($b, $a % $b) : $a; };
verdy_p 12-Dec-2012 11:38
Note that fmod is NOT equivalent to this basic function:

<?php
 function modulo($a, $b) {
    return $a - $b * floor($a / $b);
 }
?>

because fmod() will return a value with the same sign as $a. In other words the floor() function is not correct as it rounds towards -INF instead of towards zero.

To emulate fmod($a, $b) the correct way is:

<?php
 function fmod($a, $b) {
   return $a - $b * (($b < 0) ? ceil($a / $b) : floor($a / $b)));
 }
?>

Note that both functions will throw a DIVISION BY ZERO if $b is null.

The first function modulo() above is the mathematical function which is useful for working on cyclic structures (such as calender computions or trignonometric functions :

- fmod($a, 2*PI) returns a value in [0..2*PI) if $a is positive
- fmod($a, 2*PI) returns a value in [-2*PI..0] if $a is negative
- modulo($a, 2*PI) returns a value always in [0..2*PI) independantly of the sign of $a
dePijd 10-Feb-2010 03:37
This class ran through several unit tests and fixes all failures found in bugs.php.net

<?php
abstract class MyNumber {
    public static function isZero($number, $precision = 0.0000000001)
    {
        $precision = abs($precision);
        return -$precision < (float)$number && (float)$number < $precision;
    }
    public static function isEqual($number1, $number2)
    {
        return self::isZero($number1 - $number2);
    }
    public static function fmod($number1, $number2)
    {
        $rest = fmod($number1, $number2);
        if (self::isEqual($rest, $number2)) {
            return 0.0;
        }
        if (mb_strpos($number1, ".") === false) {
            $decimals1 = 0;
        } else {
            $decimals1 = mb_strlen($number1) - mb_strpos($number1, ".") - 1;
        }
        if (mb_strpos($number2, ".") === false) {
            $decimals2 = 0;
        } else {
            $decimals2 = mb_strlen($number2) - mb_strpos($number2, ".") - 1;
        }
        return (float)round($rest, max($decimals1, $decimals2));
    }
}
?>
linkboss at gmail dot com 18-Oct-2009 02:49
You can also use the modulo operator '%', which returns the same result :

<?php
$var1 = 5;
$var2 = 2;

echo $var1 % $var2; //Returns 1
echo fmod($var1,$var2); //Returns the same
?>
matrebatre 20-May-2008 09:09
I always use this:

function modulo($n,$b) {
return $n-$b*floor($n/$b);
}

And it appears to work correctly.
ysangkok at gmail dot com 01-Jul-2007 06:37
Please note that this:
<?php
function custom_modulo($var1, $var2) {
  $tmp = $var1/$var2;

  return (float) ( $var1 - ( ( (int) ($tmp) ) * $var2 ) );
}

$par1 = 1;
$par2 = 0.2;

echo "fmod:          ";
var_dump(fmod ( $par1 , $par2 ));
echo "custom_modulo: ";
var_dump(custom_modulo ( $par1 , $par2 ));
?>

gives this:

fmod:          float(0.2)
custom_modulo: float(0)

Fmod does not deliver the desired result, therefore I made my own.
cory at lavacube dot net 09-Dec-2005 07:13
I don't believe that is correct.

Try this out using your patch:
<?php

echo duration( mktime(0, 0, 0, 1, 0, 2006)-time() );

?>

As of right now, this will read:
1 month, 22 days, 24 hours, 49 minutes, 15 seconds

Which is completely incorrect. Seeing as how it is the 9th of December.

The real real flaw here is how the 'year' and 'month' periods are calculated. As most months vary in length...

Thank you very much SnakeEater251 for pointing this out.

The quickest way to get slightly more accurate results, is to use averages based on one "true" year, which is 365.25 days.

Change the year and month to:
      'year'       => 31557600, // one 'true year' (365.25 days)
      'month'    => 2629800, // one 'true year' divided by 12 :-)

I will work on developing a true fix, for pin-point accuracy. ;-)

 - Cory Christison
SnakeEater251 27-Nov-2005 07:16
Note on the code given by cory at lavacube dot net.
You will recieve better results by not using floor and using round instead. As you continue increasing to larger amounts of time you will notice that the outputted time is off by large amounts.

so instead of $temp = floor( $int_seconds / $length );
we would use  $temp = round( $int_seconds / $length );

<?php

function duration( $int_seconds=0, $if_reached=null )
{
   $key_suffix = 's';
   $periods = array(
                   'year'        => 31556926,
                   'month'        => 2629743,
                   'day'        => 86400,
                   'hour'        => 3600,
                   'minute'    => 60,
                   'second'    => 1
                   );

   // used to hide 0's in higher periods
   $flag_hide_zero = true;

   // do the loop thang
   foreach( $periods as $key => $length )
   {
       // calculate
       $temp = round( $int_seconds / $length );

       // determine if temp qualifies to be passed to output
       if( !$flag_hide_zero || $temp > 0 )
       {
           // store in an array
           $build[] = $temp.' '.$key.($temp!=1?'s':null);

           // set flag to false, to allow 0's in lower periods
           $flag_hide_zero = false;
       }

       // get the remainder of seconds
       $int_seconds = fmod($int_seconds, $length);
   }

   // return output, if !empty, implode into string, else output $if_reached
   return ( !empty($build)?implode(', ', $build):$if_reached );
}

?>
cory at lavacube dot net 26-Nov-2005 09:38
A more formal way for generating duration strings:

<?php

function duration( $int_seconds=0, $if_reached=null )
{
    $key_suffix = 's';
    $periods = array(
                    'year'        => 31556926,
                    'month'        => 2629743,
                    'day'        => 86400,
                    'hour'        => 3600,
                    'minute'    => 60,
                    'second'    => 1
                    );

    // used to hide 0's in higher periods
    $flag_hide_zero = true;

    // do the loop thang
    foreach( $periods as $key => $length )
    {
        // calculate
        $temp = floor( $int_seconds / $length );

        // determine if temp qualifies to be passed to output
        if( !$flag_hide_zero || $temp > 0 )
        {
            // store in an array
            $build[] = $temp.' '.$key.($temp!=1?'s':null);

            // set flag to false, to allow 0's in lower periods
            $flag_hide_zero = false;
        }

        // get the remainder of seconds
        $int_seconds = fmod($int_seconds, $length);
    }

    // return output, if !empty, implode into string, else output $if_reached
    return ( !empty($build)?implode(', ', $build):$if_reached );
}

?>

Simple use:
<?php

    echo duration( mktime(0, 0, 0, 1, 1, date('Y')+1) - time(), 'Some fancy message to output if duration is already met...' );

?>

Enjoy. :-)
cory at simplesystems dot ca 23-Nov-2005 02:39
Just a note on the previous note by Ryan Means:

Instead of using explode() to get the number before the decimal point, would be to use floor()... floor() rounds fractions down, which is exactly what is needed.

His same example using floor();

<?PHP
$totalsec=XXXXXXX; //Replace the X's with a int value of seconds

$daysarray = floor( $totalsec/86400 );

$partdays = fmod($totalsec, 86400);
$hours = floor( $partdays/3600 );

$parthours = fmod($partdays, 3600);
$min = floor( $parthours/60 );

$sec = fmod($parthours, 60);

echo "days " . $days . "<br>";
echo "hours " . $hours . "<br>";
echo "minutes " . $min . "<br>";
echo "seconds " . $sec . "<br>";
?>
Ryan Means 11-May-2005 03:15
If your given a number of seconds and you want to turn it into Days, hours, minutes, and seconds:
(this is very useful when using the Unix Time Epoch to find the difference from one time to the other)

For Example:
I posted in a bb at one date.. when I post a Unix Time Epoch was marked..
Then When I go back and view it again 2 weeks later I generate the Unix Time Epoch for the current time.
Then take the current time - the posting time, this gives the number of seconds since the post.
Then use the below equations to get days, hours, minutes, and seconds since the post was made:

<?PHP
$totalsec=XXXXXXX; //Replace the X's with a int value of seconds

$daysarray = explode(".", ($totalsec/86400));
$days = $daysarray[0];

$partdays = fmod($totalsec, 86400);
$hoursarray = explode(".", ($partdays/3600));
$hours = $hoursarray[0];

$parthours = fmod($partdays, 3600);
$minarray = explode(".", ($parthours/60));
$min = $minarray[0];

$sec = fmod($parthours, 60);

echo "days " . $days . "<br>";
echo "hours " . $hours . "<br>";
echo "minutes " . $min . "<br>";
echo "seconds " . $sec . "<br>";
?>
sam dot fullman at verizon 24-Feb-2005 04:29
This function behaves wierd in negative regions.  If you have something like an angle that goes through 360 degress of rotation and your angle goes negative, then fmod of -1 should be 359, right?

Here's a way to get that result, so that you get a phase shift vs. just a "negative fmod":

$h= -30; //same as 330 degrees

//handle negative
if($h<0){
    while(true){
        $fail++; if($fail>100)break; //in case loop gets tied up
        $h+=360;
        if($h>=0)break;
    }
}
$h=fmod($h,360);

echo $h;  //will say 330 degrees - we phase shifted up until positive.
rocan 20-Feb-2005 03:10
john at digitizelife dot com:

Well not sure how your comment applys to fmod..

but their is a sure simpler way of coping with situations like this..

its called a bit field (bit masking)
 
e.g.

/* Categories */
bin     dec   cat
0001 - 1 - Blue
0010 - 2 - Red
0100 - 4 - Green 
1000 - 8 - Yellow

/* Permissions */
0010 - 2   - Bob
0101 - 5    - John
1011 - 11  - Steve
1111-  15 - Mary

to find out the permissions for each user you simple need to do a bitwise AND 

$steve_auth=11;

function get_perm($auth)
{
    $cats["Blue"]=1;
    $cats["Red"]=2;
    $cats["Green"]=4;
    $cats["Yellow"]=8;
    $perms=array();
    foreach($cats as $perm=>$catNum)
    {
          if($auth & $catNum)
                $perms[$perm]=true;

    }

    return $perms;
}

print_r(get_perm($steve_auth));
/*
returns
Array
(
    [Blue] => 1
    [Red] => 1
    [Yellow] => 1
)
*/

This is far simpler than your prime number idea, in fact you dont even need a function in any tests for the permmsions on a user you can do them directly using the bitwise and operator.

You may want to read the following

http://en.wikipedia.org/wiki/Bitmask
http://uk2.php.net/manual/en/language.operators.bitwise.php
jphansen at uga dot edu 10-Jan-2005 08:44
fmod() does not mirror a calculator's mod function. For example, fmod(.25, .05) will return .05 instead of 0 due to floor(). Using the aforementioned example, you may get 0 by replacing floor() with round() in a custom fmod().

<?
function fmod_round($x, $y) {
    $i = round($x / $y);
    return $x - $i * $y;
}

var_dump(fmod(.25, .05)); // float(0.05)
var_dump(fmod_round(.25, .05)); // float(0)
?>
konstantin at rekk dot de 27-May-2004 05:10
If you need to reduce an integer to zero if zero and 1 if not, you can use

$sign = (integer)(boolean)$integer;

instead of

$sign = $integer > 0 ? 1 : 0;

it is faster from 100 operations on (at least on my machine).
alex at xelam dot net 16-Feb-2004 10:19
Integer Modulo

If you want the remainder of the division of two Integers rather than Floats, use "%"; eg:

<?php
$a = 4;
$b = 3;

print($a % $b);
?>

Will output "1".
picaune at hotmail dot com 10-Mar-2003 12:57
NAN (.net Equivalent = Double.NaN) means "Not-a-Number".
Some ways to get NaN are modulo 0, and square root of 0.