Edit report at https://bugs.php.net/bug.php?id=61855&edit=1
ID: 61855
User updated by:martin dot edlman at gmail dot com
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:
Thanks for explanation, I'll modify PHP code to do some round()s or casts to
float to get expected results.
I used float instead of double (which uses less decimal points) in my C code,
so I got correct results.
#include
#include
int main(char **argv, int argc) {
float a = 1.2;
float b = 0.4;
float 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));
}
v(15) = 3.000
v(16) = 3.
v = 3.00
floor(v) = 3.00
Previous Comments:
[2012-04-26 07:51:41] ras...@php.net
And just for the record, no, the same C code definitely does not return the
"correct numbers" as you put it:
#include
#include
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) = 3.000
v(16) = 2.9996
v = 3.00
floor(v) = 2.00
That looks remarkably like the PHP output.
[2012-04-26 07:33:20] paj...@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
2.999 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:
---
Expected result:
v(15) = 3.000
v(16) = 3.
v = 3
floor(v) = 3
Actual result:
--
v(15) = 3.000
v(16) = 2.9996
v = 3
floor(v) = 2
--
Edit this bug report at https://bugs.php.net/bug.php?id=61855&edit=1
