Bug #78606 [Nab]: Wrong calculation when dealing with bigint

Edit report at https://bugs.php.net/bug.php?id=78606&edit=1 ID: 78606 Updated by: cmb@php.net Reported by: marcelotpcruz at gmail dot com Summary: Wrong calculation when dealing with bigint Status: Not a bug Type: Bug Package: Math related Operating System: Windows/Unix PHP Version: 7.3.10 Assigned To: cmb Block user comment: N Private report: N New Comment: The quote you've cited is from the section "Converting to integer – From floating point numbers"[1] and as such is irrelevant here. What is relevant is that integral floats are not exact beyond ~ 2**53 (assuming IEEE 754 doubles). Also note that number_format() expects a float, and if you're passing an int, it is converted to float. [1] <https://www.php.net/manual/en/language.types.integer.php#language.types.integer.casting.from-float> Previous Comments: ------------------------------------------------------------------------ [2019-09-29 15:31:05] marcelotpcruz at gmail dot com Good day! According to the manual: "If the float is beyond the boundaries of integer (usually +/- 2.15e+9 = 2^31 on 32-bit platforms and +/- 9.22e+18 = 2^63 on 64-bit platforms other than Windows), the result is undefined, since the float doesn't have enough precision to give an exact integer result." $someInt = pow(2, 55); echo $someInt . '<br>'; echo number_format($someInt-10, 0, '.', ''); $someInt = (float)pow(2,55); echo $someInt . '<br>'; $someInt -= 10; echo (int)$someInt . '<br>'; In the samples I'm using number_format with a 2^55(36028797018963968) - 10, on a 64 bit system, shouldn't it give me 36028797018963958 instead of 36028797018963960? Maybe the docs need to be updated or this looks like a bug. ------------------------------------------------------------------------ [2019-09-29 08:32:16] cmb@php.net Thank you for taking the time to write to us, but this is not a bug. Please double-check the documentation available at http://www.php.net/manual/ and the instructions on how to report a bug at http://bugs.php.net/how-to-report.php See <https://www.php.net/manual/en/language.types.integer.php#language.types.integer.overflow> and <https://www.php.net/manual/en/language.types.float.php>. ------------------------------------------------------------------------ [2019-09-29 02:55:11] marcelotpcruz at gmail dot com Description: ------------ Using a 64 bit install on a 64 bit system: Test script: --------------- <?php $someInt = 36028797018963968;//2^55 echo $someInt . '<br>'; echo number_format($someInt, 10, '.', '') . '<br>'; $someInt-= 10; if((PHP_INT_MAX + 1) === (PHP_INT_MAX + 2)) //This should be false echo 'This should never be echoed<br>'; echo number_format($someInt, 10, '.', '') . '<br>';//Value here is just $someInt minus 10 $maxInt = PHP_INT_MAX; echo $maxInt . '<br>'; echo ++$maxInt . '<br>'; echo --$maxInt . '<br>';//Should print 9223372036854775807 echo number_format(PHP_INT_MAX, 0, '.', '') . '<br>';//Should print 9223372036854775807 Expected result: ---------------- 36028797018963968 36028797018963968.0000000000 36028797018963958.0000000000 9223372036854775807 9.2233720368548E+18 9223372036854775807 9223372036854775807 Actual result: -------------- 36028797018963968 36028797018963968.0000000000 This should never be echoed 36028797018963960.0000000000 9223372036854775807 9.2233720368548E+18 9.2233720368548E+18 9223372036854775808 ------------------------------------------------------------------------ -- Edit this bug report at https://bugs.php.net/bug.php?id=78606&edit=1