Bug #51547 [Opn->Bgs]: Type casting from int to int after log changes value

Edit report at http://bugs.php.net/bug.php?id=51547&edit=1 ID: 51547 Updated by: degeberg@php.net Reported by: acollins at liv dot ac dot uk Summary: Type casting from int to int after log changes value -Status: Open +Status: Bogus Type: Bug Package: *Math Functions PHP Version: 5.2.13 New Comment: Floating point values have a limited precision. Hence a value might not have the same string representation after any processing. That also includes writing a floating point value in your script and directly printing it without any mathematical operations. If you would like to know more about "floats" and what IEEE 754 is, read this: http://docs.sun.com/source/806-3568/ncg_goldberg.html Thank you for your interest in PHP. Try having a look at this: echo serialize(log(1000, 10)); When you cast to int you just truncate the fractional part. Previous Comments: ------------------------------------------------------------------------ [2010-04-13 11:04:47] acollins at liv dot ac dot uk Note: I assume this is because log() returns a floating point value. I.e. it's a precision issue? ------------------------------------------------------------------------ [2010-04-13 11:03:32] acollins at liv dot ac dot uk Description: ------------ When performing a log(), and immediately type casting afterwards, the value changes. Test script: --------------- <?php $val = 1000; echo log($val, 10) .' == '. (int) log($val, 10); ?> Expected result: ---------------- 3 == 3 Actual result: -------------- 3 == 2 ------------------------------------------------------------------------ -- Edit this bug report at http://bugs.php.net/bug.php?id=51547&edit=1