Bug #74925 [Nab]: Mismatching floating values

Edit report at https://bugs.php.net/bug.php?id=74925&edit=1

 ID:                 74925
 User updated by:    tuepp at gmx dot de
 Reported by:        tuepp at gmx dot de
 Summary:            Mismatching floating values
 Status:             Not a bug
 Type:               Bug
 Package:            PHP Language Specification
 Operating System:   Windows
 PHP Version:        7.0.21
 Block user comment: N
 Private report:     N

 New Comment:

I know about this issue - and I wonder why there shouldn't be some internal rounding-mechanism.

"Thank you for your interest in PHP." - that must be a bad joke...


Previous Comments:
------------------------------------------------------------------------
[2017-07-14 14:49:38] [email protected]

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.



------------------------------------------------------------------------
[2017-07-14 14:42:09] tuepp at gmx dot de

Description:
------------
Floating number comparison fails for numbers that have to be rounded internal.
This bug may be over 10 years old. I've reported it 5 years ago and it is still not fixed. Now I have an example with one instead of 3 lines of code what might be more shoking. I've documented this bug in my final exam 6 years ago and it feeled like I got some extra points for it - so thank you. But now it's really time to fix it! I'm not sure if I'll report it a third time in another 5 years... So go, get it!

Test script:
---------------
<?php
echo (54.83 + 0.01 == 54.84) ? 'ok' : 'fail'; //fail
echo "<br>\n";
echo ((3 * 202.3) == 606.9) ? 'ok' : 'fail'; //fail
echo "<br>\n";
for($v = -1; $v < 0; $v += 0.2){
	echo "$v; "; // -1; -0.8; -0.6; -0.4; -0.2; -5.5511151231258E-17;
}

Expected result:
----------------
ok
ok
-1; -0.8; -0.6; -0.4; -0.2 

Actual result:
--------------
fail
fail
-1; -0.8; -0.6; -0.4; -0.2; -5.5511151231258E-17;


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Edit this bug report at https://bugs.php.net/bug.php?id=74925&edit=1