algorithm - How to round down to the nearest significant figure in php

Question

Is there any slick way to round down to the nearest significant figure in php?

So:

0->0
9->9
10->10
17->10
77->70
114->100
745->700
1200->1000

?

Answer 1

$numbers = array(1, 9, 14, 53, 112, 725, 1001, 1200);
foreach($numbers as $number) {
    printf('%d => %d'
            , $number
            , $number - $number % pow(10, floor(log10($number)))
            );
    echo "
";
}

Unfortunately this fails horribly when $number is 0, but it does produce the expected result for positive integers. And it is a math-only solution.