mgmarcum

Last reply - and I promise I will never post here again: mmarcum@blackbird:~$ cat test.cc #include <iostream> using namespace std; int main() { cout << (206.8008-15.7608-191.04) << endl; return 0; } mmarcum@blackbird:~$ g++ test.cc mmarcum@blackbird:~$ ./a.out 2.84217e-14 mmarcum@blackbird:~$ Unfrickinbelievable

This is Insane, All I want to do is subtract three floating point numbers and get the right answer. So does openoffice spreadsheet and my linux calculator use a special library? Whats the point of using an ieee compliant floating point processor if its going to give the wrong answer?

So I'm sure someone has seen this before, but I couldn't find a mention of it anywhere. I've replicated this on 3 different php installs: echo (206.8008-15.7608-191.04); the output is: 2.84217094304E-14 wtf?!?! This is simple subtraction! I've also tried echo 206.8008-15.7608-191.04; and echo ((206.8008-15.7608)-191.04); all of them output 2.84217094304E-14 Ok, so this is some type of float/double conversion type bug right? echo (((double)206.8008-(double)15.7608)-(double)191.04); echo (((float)206.8008-(float)15.7608)-(float)191.04); same output. and jst for the hell of it $var= (((float)206.8008-(float)15.7608)-(float)191.04); echo $var; same thing: 2.84217094304E-14 funny thing is that echo (206.8008-15.7608) gives 191.04 so you'd think echo (206.8008-15.7608)-191.04 would output the correct answer. I noticed this because I was using money_format and it was returning -0.00 (yes with the negative sign in front) which is a little closer to the real answer but still incredibly dumb. started trying to debug this and when I echoed out the math that was getting passed to money format I nearly spilled my coffee... verified on these two php versions (cli and apache module) PHP 5.3.2-1ubuntu4 with Suhosin-Patch (cli) (built: Apr 9 2010 08:18:14) PHP 5.1.6 (cli) (built: Jan 4 2010 10:45:55) Can someone tell me what the hell is going here? I'm trying to do simple tax calculations on an ecommerce site. I've been doing php developement for about 7 years now and this is the first time I've ever seen anything like this. All the other php devs in my office are stumped and amazed too.