exp

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

exp — 计算 e 的指数

说明

exp(float $num): float

返回 e 的 num 次方值。

注意:
用“e”作为自然对数的底数，大约为 2.718282。

参数

num: 要处理的参数

返回值

'e' raised to the power of num

示例

示例 #1 exp() 示例

<?php
echo exp(12) . "\n";
echo exp(5.7);
?>

以上示例会输出：

1.6275E+005
298.87

参见

log() - 自然对数
pow() - 指数表达式

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zooly at globmi dot com ¶

14 years ago

PHP does not have the following math function in any extensions:

frexp() - Extract Mantissa and Exponent of the Floating-Point Value

I've digged many C source codes, and found the simplest implementation as follows:

<?php

function frexp ( $float ) {

  $exponent = ( floor(log($float, 2)) + 1 );
  $mantissa = ( $float * pow(2, -$exponent) );

  return(
    array($mantissa, $exponent)
  );

}

print_r(frexp(0.0345));
print_r(frexp(21.539));

?>

Array
(
    [0] => 0.552
    [1] => -4
)
Array
(
    [0] => 0.67309375
    [1] => 5
)

I have compared the results using a lot of floats against C's frexp function - they are the same.

Note that C and PHP uses different float precisions, for example "4619.3" gives:

C: 0.56387939453125, 13
PHP: 0.563879394531, 13

/Assuming default configurations./