Bug #61855 [Nab]: Wrong division of float numbers

Edit report at https://bugs.php.net/bug.php?id=61855&edit=1 ID: 61855 Updated by: rasmus@php.net Reported by: martin dot edlman at gmail dot com Summary: Wrong division of float numbers Status: Not a bug Type: Bug Package: Math related Operating System: Linux PHP Version: 5.3.10 Block user comment: N Private report: N New Comment: And just for the record, no, the same C code definitely does not return the "correct numbers" as you put it: #include <stdio.h> #include <math.h> int main(char *argv[], int argc) { double a = 1.2; double b = 0.4; double v = a/b; printf("v(15) = %.15f\n", v); printf("v(16) = %.16f\n", v); printf("v = %f\n", v); printf("floor(v) = %f\n",floor(v)); } That, I hope you would agree, is the closest thing to the same C code. % cc a.c -o a -lm % ./a v(15) = 3.000000000000000 v(16) = 2.9999999999999996 v = 3.000000 floor(v) = 2.000000 That looks remarkably like the PHP output. Previous Comments: ------------------------------------------------------------------------ [2012-04-26 07:33:20] pajoye@php.net 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. ------------------------------------------------------------------------ [2012-04-26 06:53:50] martin dot edlman at gmail dot com Description: ------------ --- From manual page: http://www.php.net/function.floor#refsect1-function.floor-description --- I encountered problem when dividing float numbers. It's simple formula which can be solved by 10 year old child. But not by PHP! See example. The problem is that displayed value (3) doesn't correspond with internal value 2.999999999999999 and floor() then returns 2 which is obviously incorrect result! And that's serious problem. The same code in C returns correct numbers. Test script: --------------- <?php $a = 1.2; $b = 0.4; $v = $a / $b; printf("v(15) = %.15f\n", $v); printf("v(16) = %.16f\n", $v); print "v = $v\n"; print "floor(v) = ".floor($v)."\n"; ?> Expected result: ---------------- v(15) = 3.000000000000000 v(16) = 3.0000000000000000 v = 3 floor(v) = 3 Actual result: -------------- v(15) = 3.000000000000000 v(16) = 2.9999999999999996 v = 3 floor(v) = 2 ------------------------------------------------------------------------ -- Edit this bug report at https://bugs.php.net/bug.php?id=61855&edit=1