Validating number precision/scale

Question

How would I validate the precision/scale of a number posted from a form to make sure it can be stored in an Oracle NUMBER column? For example:

<input type="number" name="foo" value="123.45" />

The user submits the form to the PHP backend...

<?php
function isValidNumber($number, $precision, $scale) {
    // ???

    return $isValid;
}

// The precision and scale here are actually dynamic
$isValid = isValidNumber($_POST['foo'], 5, 2);

...where I would like to be able to validate the number without trying to insert/update it in Oracle and handle any precision overflow errors (proactive design, rather than reactive). I have not been able to come up with a method of accurately validating all the various fringe cases (Oracle doesn't produce errors for scale overflow - it just rounds to the maximum, but this rounding could lead to precision overflows, which do produce errors, etc.).

Answer 1

function isValidNumber($number, $precision, $scale) {
    $isValid = false;
    if (is_numeric($number)) {
        $num = round(abs($number), $scale);
        $max = str_repeat('9',$precision - $scale).'.'.str_repeat('9',$scale);
        $isValid = $num <= $max;
    }
    return $isValid;
}

Output for isValidNumber($number, 5, 2)

123.456   (valid)
9999.999  (invalid)
99999.999 (invalid)
12.003    (valid)
999.99    (valid)
999.999   (invalid)
1234.5    (invalid)

and finally

isValid(1234567890123456789012345678.90, 30, 2) == **valid**