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Bug #77675 Floating Value Bug
Submitted: 2019-02-27 14:14 UTC Modified: 2019-02-27 14:31 UTC
From: joni dot ttv at gmx dot de Assigned: cmb (profile)
Status: Not a bug Package: Math related
PHP Version: 7.2.15 OS: Debian, Mac OS
Private report: No CVE-ID: None
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 [2019-02-27 14:14 UTC] joni dot ttv at gmx dot de

there is a problem when adding float values:

If you add 76.50 + 15.96 + 7.54 the result ist 100.00. If you var_dump the sum the result is also 100.00. But when you compare the sum and 100.00 the result is that they are not equal.
If you swap the last two numbers, the sum is correct and also the comparison.

Test script:

// Prints 100
var_dump(76.50 + 15.96 + 7.54);

// Prints false (should be true)
var_dump((76.50 + 15.96 + 7.54) == 100.00);

// Prints false (should be true)
var_dump((76.50 + 15.96 + 7.54) == (76.50 + 7.54 + 15.96));

Expected result:

Actual result:


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 [2019-02-27 14:31 UTC]
-Status: Open +Status: Not a bug -Assigned To: +Assigned To: cmb
 [2019-02-27 14:31 UTC]
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:

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