Cara menggunakan log() function in php

(PHP 4, PHP 5, PHP 7, PHP 8)

log — Natural logarithm

Description

log(float $num, float $base = M_E): float

Parameters

The value to calculate the logarithm for

The optional logarithmic base to use (defaults to 'e' and so to the natural logarithm).

Return Values

The logarithm of num to base, if given, or the natural logarithm.

See Also

• log10() - Base-10 logarithm
• exp() - Calculates the exponent of e
• pow() - Exponential expression

c0x at mail dot ru ¶

17 years ago

more general version, works fine on negative, very big ($value > 1E+18) and very small ($value < 1E-18) numbers.

function expn($value, $prec = 3, $base = 1000, $prefix = '') {
    $e = array('a', 'f', 'p', 'n', 'u', 'm', '', 'k', 'M', 'G', 'T', 'P', 'E');
    $p = min(max(floor(log(abs($value), $base)), -6), 6);
    return round((float)$value / pow($base, $p), $prec) . $prefx . $e[$p + 6];
}

olafurw [at] gmail.com ¶

13 years ago

For those interested. Works with older than 4.3 versions.

    function byteConvert($bytes)
    {
        $s = array('B', 'Kb', 'MB', 'GB', 'TB', 'PB');
        $e = floor(log($bytes)/log(1024));

              return

ClaudiuS ¶

9 years ago

If you just need to check if N is a perfect power of Base, log() is SLOW compared to a WHILE construct that will be 2x faster!

Tested on range: 1 ... 20.000.000 => while() is 2.105 times faster

$number

mcmeijer at yahoo dot com ¶

17 years ago

$val = 1000000
$val2 = floor(log($val,10)) gives a value of 5 for $val2 and not 6 as expected.
$val2 = floor(log10($val)) gives the correct value.

rhinopete at batpudding dot com ¶

3 years ago

Seems like unit prefixes should have a standard PHP function.  Maybe in the future.

I found this page while looking for a quick unit prefix function.  The one by  olafurw was voted down, I think because it had unchecked array indexes and /0s.  So here it is fixed and readable.

-Should work down to PHP 4.
-Not meant for fractions or negatives, so anything less than 1 returns 0.
-Not very effective on really really large numbers, but it's easy to add more prefixes.
-Doesn't handle non numeric arguments. PHP 7+ can do this: function binaryprefix( int $units, $unit = '' )

// returns reduced $units with a binary prefix
// ex. ( 110974120, 'B' ) == 105.8MiB
// ex. ( 2^100, 'B' ) == 1048576.0YiB
// ex. ( 0.12314, 'B' ) == 0B
function binaryprefix( $units, $unit = '' )
{
    $prefix = array('', 'Ki', 'Mi', 'Gi', 'Ti', 'Pi', 'Ei', 'Zi', 'Yi');
    $exponent = min( floor( log( max( 1, $units ), 1024 ) ), count( $prefix ) - 1 );

    if ( $units < 1024 )
        return sprintf( '%d%s%s', max( 1, $units + 1 ) - 1, $prefix[$exponent], $unit );
    else
        return sprintf( '%.1f%s%s', $units / pow(1024, $exponent), $prefix[$exponent], $unit );
}

https://en.wikipedia.org/wiki/Binary_prefix#Adoption_by_IEC.2C_NIST_and_ISO

Also more colloquially:
    $prefix = array('', 'k', 'm', 'g', 't', 'p', 'e', 'z', 'y');

admin at worldtakeover dot tk ¶

18 years ago

In regards to the note about log in base 10 and the round() function. You need to use floor() instead of round() to find out the order of magnitude. That way, you don't have to worry about subtracting 0.5 or whatever.

dingus_76 at hotmail dot com ¶

14 years ago

well i been pulling my hair out trying to get log to work with big numbers and i ended up writing a bclog function so to save everyone else the stress here it is

function bclog($X,$base=10,$decimalplace=12){
    $integer_value=0;
    while($X < 1){
        $integer_value = $integer_value - 1 ;
        $X = bcmul($X , base);
    }
    while($X >= $base){
        $integer_value = $integer_value + 1;
        $X = bcdiv($X , $base );
    }
    $decimal_fraction = 0.0;
    $partial = 1.0;
    # Replace X with X to the 10th power
    $X = bcpow($X , 10);
    while($decimalplace > 0){
        $partial = bcdiv($partial , 10);
        $digit=0;
        while($X >= $base){
              $digit = $digit + 1;
              $X = bcdiv($X , $base);
        }
        $decimal_fraction = bcadd($decimal_fraction , bcmul($digit , $partial));
        # Replace X with X to the 10th power
        $X = bcpow($X , 10);
        $decimalplace = $decimalplace - 1 ;
    }
    return $integer_value + $decimal_fraction ;
}
?>

Ulf Wostner ¶

16 years ago

#--------------------------------------------------------
#     How many digits does an integer have?
#--------------------------------------------------------function digit_count($n, $base=10) {

  if(