PHP：将数字四舍五入为16位小数

Question

Hi I'm trying to rounding a number into the 16 decimal digits but it only show and doesn't round up till 14 decimal digit .

Here's my attempt:

<?php

$num= 0.16346153846153846;

$round = number_format((float)$num, 17, '.', '');

echo $round * -1;
?>

OUTPUT:

-0.16346153846154

EXPECTED OUTPUT:

0.1634615384615385

I know that float is only 14 decimal digits. Is there any other way around for the 16 decimal digits ?

Answer 1

You can set this parameters at run-time. 16 digits is usually the maximum value on most platforms, larger values giving only meaningless or "fictional" digits:

ini_set("precision", "16");

See Changing precision level floating-point variables

Answer 2

Can you try doing this, & see what happens? (May not be the best way of dealing with floats and numbers though)

$num = 0.16346153846153846;
$new_num = $num * -1;
echo number_format((float)$new_num, 17);

Multiply first, then try rounding the result.

Answer 3

number_format and the precision INI setting uses float , which is likely to result in unexpected behaviour if you're rounding to that many decimal digits.

You can alternatively use the PHP decimal extension with $decimal->toFixed(16) or $decimal->round(16) to achieve this with guaranteed accuracy regardless of your INI.

Answer 4

Recently we experienced an issue with the reading of amount(decimal number) from an excel file which has a decimal number with more than 14 digits after the decimal. The issue is fixed after using the option of an advanced algorithm for converting the decimal number. For this, we need to set,

ini_set('precision', -1);

Ref: http://php.net/precision