PHP Australia Conference 2015

# fmod

(PHP 4 >= 4.2.0, PHP 5)

fmodReturns the floating point remainder (modulo) of the division of the arguments

### Description

float fmod ( float `\$x` , float `\$y` )

Returns the floating point remainder of dividing the dividend (`x`) by the divisor (`y`). The remainder (r) is defined as: x = i * y + r, for some integer i. If `y` is non-zero, r has the same sign as `x` and a magnitude less than the magnitude of `y`.

`x`

The dividend

`y`

The divisor

### Return Values

The floating point remainder of `x`/`y`

### Examples

Example #1 Using fmod()

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

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### User Contributed Notes 18 notes

cory at lavacube dot net
8 years ago
``` I don't believe that is correct.Try this out using your patch:<?phpecho 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 secondsWhich 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
8 years ago
``` 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 );<?phpfunction 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 );}?> ```
picaune at hotmail dot com
11 years ago
``` NAN (.net Equivalent = Double.NaN) means "Not-a-Number".Some ways to get NaN are modulo 0, and square root of 0. ```
verdy_p
1 year ago
``` 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 ```
matrebatre
6 years ago
``` I always use this:function modulo(\$n,\$b) {return \$n-\$b*floor(\$n/\$b);}And it appears to work correctly. ```
cory at lavacube dot net
8 years ago
``` A more formal way for generating duration strings:<?phpfunction 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. :-) ```
konstantin at rekk dot de
10 years ago
``` 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). ```
rocan
9 years ago
``` 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   cat0001 - 1 - Blue 0010 - 2 - Red 0100 - 4 - Green  1000 - 8 - Yellow/* Permissions */0010 - 2   - Bob0101 - 5    - John1011 - 11  - Steve1111-  15 - Maryto 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/Bitmaskhttp://uk2.php.net/manual/en/language.operators.bitwise.php ```
cory at simplesystems dot ca
8 years ago
``` 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
9 years ago
``` 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>";?> ```
dePijd
4 years ago
``` This class ran through several unit tests and fixes all failures found in bugs.php.net<?phpabstract 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));    }}?> ```
ysangkok at gmail dot com
7 years ago
``` Please note that this:<?phpfunction 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. ```
KRAER
8 months ago
``` 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);?> ```
alex at xelam dot net
10 years ago
``` Integer ModuloIf 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". ```
jphansen at uga dot edu
9 years ago
``` 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)?> ```
Adrien Gibrat
1 year ago
``` 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'); // === 14If 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'); // ~= 1.232You can use a closure in PHP 5.3 :    \$gcd = function (\$a, \$b) use (&\$gcd) { return \$b ? \$gcd(\$b, \$a % \$b) : \$a; }; ```
linkboss at gmail dot com
4 years ago
``` You can also use the modulo operator '%', which returns the same result :<?php\$var1 = 5;\$var2 = 2;echo \$var1 % \$var2; //Returns 1echo fmod(\$var1,\$var2); //Returns the same?> ```
sam dot fullman at verizon
9 years ago
``` 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 negativeif(\$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. ```