floating point - Truncate float numbers with PHP

Question

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

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

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

45.8976 => 45.90, 0.0185 => 0.02

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 ) );
}

Answer 1

floor will do as you ask.

floor(45.8976 * 100) / 100;

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?