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.

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

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 ];
}

//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

Ulf Wostner ¶

16 years ago