Bug #80163 [Opn->Nab]: An error in operating a cast to an int

Edit report at https://bugs.php.net/bug.php?id=80163&edit=1 ID: 80163 Updated by: requinix@php.net Reported by: peter dot j dot burling at skymesh dot com dot au Summary: An error in operating a cast to an int -Status: Open +Status: Not a bug Type: Bug Package: Math related Operating System: Linux - Fedora fc30.x86_64 PHP Version: 7.3.22 Block user comment: N Private report: N 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://www.floating-point-gui.de/ Thank you for your interest in PHP. Previous Comments: ------------------------------------------------------------------------ [2020-09-30 01:44:15] peter dot j dot burling at skymesh dot com dot au Description: ------------ Casting to an int where a subtraction equals 0.2, when multiplied by 10 and cast to an int returns a value of 1. If the subtraction equals 0.3 then the result of the above cast will equal 3 Test script: --------------- $kwatts = ((int)(($row[7]Â - $row[4]) * 10))/10 ; with $row[7] = 55.40 with $row[4] = 55.20 but returning a $kwatts value of 0.1 php > $a = 0.1; php > $b = 0.3; php > echo $b - $a ; 0.2 php > echo ($b - $a)* 10 ; 2 php > echo(int)($b - $a)* 10 ; 0 php > echo(int)(($b - $a)* 10) ; 1 php > echo(int)(10 * ($b - $a)) ; 1 php > echo(int)((10 * ($b - $a))) ; 1 ------------------------------------------------------------------------ -- Edit this bug report at https://bugs.php.net/bug.php?id=80163&edit=1