用 PHP 截断浮点数

2022-01-09 00:00:00 floating-point floating-accuracy php truncate

当一个浮点数需要在浮点数后截断到某位时，事实证明这并不容易.例如，如果必须截断到该点之后的第二个数字，则数字应该是

When a float number needs to be truncated to a certain digit after the floating point, it turns out that it is not easy to be done. For example if the truncating has to be done to second digit after the point, the numbers should be 

45.8976 => 45.89, 0.0185 => 0.01

(点后第二位不按点后第三位四舍五入).

( second digit after the point is not rounded according to the third digit after the point ).

round()、number_format()、sprintf()等函数将数字取整并打印出来

Functions like round(), number_format(), sprintf() round the number and print out

45.8976 => 45.90, 0.0185 => 0.02

我遇到了两种解决方案，我想知道它们是否足够好，哪个更好用

I have met two solutions and I am wondering if they are good enough and which one is better to be used

1.

function truncNumber( $number, $prec = 2 )
{
    return bccomp( $number, 0, 10 ) == 0 ? $number : round( $number - pow( 0.1, bcadd(   $prec, 1 ) ) * 5, $prec );
}

2.

function truncNumber($number, $prec = 2 )
{
    return sprintf( "%.".$prec."f", floor( $number*pow( 10, $prec ) )/pow( 10, $prec ) );
}

推荐答案

floor 会按照你的要求去做.

floor will do as you ask.

floor(45.8976 * 100) / 100;

你不会找到更直接的函数，因为这是一种奇怪的问题.通常你会在数学上四舍五入.出于好奇 - 你需要这个做什么?

You won't find a more direct function for this, since it's a kind of odd thing to ask. Normally you'll round mathematically correct. Out of curiosity - What do you need this for?

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