compare two float values

[neha_chhatre@yahoo.co.in]

can anybody tell me how to compare two float values
say for example
t and check are two variables declared float how to compare t and
check
please help me as soon as possible

[Joachim Schmitz]

Re: compare two float values

neha_chhatre@ya hoo.co.in wrote:

can anybody tell me how to compare two float values
say for example
t and check are two variables declared float how to compare t and
check
please help me as soon as possible

float t, check;
....
if ( t check)
printf("%f is greater than %f\n" t, check);
else
printf("%f is less than %f\n" t, check);

Don't compare for equality, won't work for float (or double), rather compare
the difference against some delta that suits your needs for accuracy

Bye, Jojo

[Joachim Schmitz]

Re: compare two float values

Joachim Schmitz wrote:

neha_chhatre@ya hoo.co.in wrote:

>can anybody tell me how to compare two float values
>say for example
>t and check are two variables declared float how to compare t and
>check
>please help me as soon as possible

float t, check;
...
if ( t check)
printf("%f is greater than %f\n" t, check);
else
printf("%f is less than %f\n" t, check);
>
Don't compare for equality, won't work for float (or double), rather
compare the difference against some delta that suits your needs for
accuracy

oops, epsilon, not delta, off by one in greek alphabeth...

[neha_chhatre@yahoo.co.in]

Re: compare two float values

actually i want to check wether two float values are equal or not
equal
i.e suppose t and t1 are two float values and i want to check wether t
and t1 are equal or not

please send in syntax form as in code form

please tell me how to do,

[Mark Bluemel]

Re: compare two float values

neha_chhatre@ya hoo.co.in wrote:

actually i want to check wether two float values are equal or not
equal
i.e suppose t and t1 are two float values and i want to check wether t
and t1 are equal or not
>
please send in syntax form as in code form

Smells like homework to me...

have you looked at the FAQ (http://www.c-faq.com)? There's a whole
section on floating point numbers, and question 14.5 is probably
close to what you want.

[santosh]

Re: compare two float values

neha_chhatre@ya hoo.co.in wrote:

actually i want to check wether two float values are equal or not
equal
i.e suppose t and t1 are two float values and i want to check wether t
and t1 are equal or not
>
please send in syntax form as in code form
>
please tell me how to do,

Please quote relevant parts of the post to which you are replying. This
is good practise on Usenet.

Comparing floats for equality is fraught with danger as many values are
not perfectly representible in binary floating point. You might find
that you need to allow for a small variation on either side of the
comparison value, just like the margin of error in scientific
experiments.

You might want to read:

<http://www.cygnus-software.com/papers/comparingfloats/Comparing%20flo ating%20point%2 0numbers.htm>
<http://docs.sun.com/source/806-3568/ncg_goldberg.ht ml>

[Kenneth Brody]

Re: compare two float values

neha_chhatre@ya hoo.co.in wrote:

>
actually i want to check wether two float values are equal or not
equal
i.e suppose t and t1 are two float values and i want to check wether t
and t1 are equal or not
>
please send in syntax form as in code form
>
please tell me how to do,

How would you check for equality if t and t1 were "int"?

How would you check for equality if t and t1 were "short"?

How would you check for equality if t and t1 were "long"?

Now, how would you check for equality if t and t1 were "float"?

Or did you have something else in mind for what "equal" means?

--
+-------------------------+--------------------+-----------------------+
| Kenneth J. Brody | www.hvcomputer.com | #include |
| kenbrody/at\spamcop.net | www.fptech.com | <std_disclaimer .h|
+-------------------------+--------------------+-----------------------+
Don't e-mail me at: <mailto:ThisIsA SpamTrap@gmail. com>

[Pietro Cerutti]

Re: compare two float values

Kenneth Brody wrote:

neha_chhatre@ya hoo.co.in wrote:

>actually i want to check wether two float values are equal or not
>equal
>i.e suppose t and t1 are two float values and i want to check wether t
>and t1 are equal or not
>>
>please send in syntax form as in code form
>>
>please tell me how to do,

>
How would you check for equality if t and t1 were "int"?
>
How would you check for equality if t and t1 were "short"?
>
How would you check for equality if t and t1 were "long"?
>
Now, how would you check for equality if t and t1 were "float"?

In a different way than above....

>
Or did you have something else in mind for what "equal" means?
>

--
Pietro Cerutti

PGP Public Key:

http://gahr.ch/pgp

[Pietro Cerutti]

Re: compare two float values

Kenneth Brody wrote:

neha_chhatre@ya hoo.co.in wrote:

>actually i want to check wether two float values are equal or not
>equal
>i.e suppose t and t1 are two float values and i want to check wether t
>and t1 are equal or not
>>
>please send in syntax form as in code form
>>
>please tell me how to do,

>
How would you check for equality if t and t1 were "int"?
>
How would you check for equality if t and t1 were "short"?
>
How would you check for equality if t and t1 were "long"?
>
Now, how would you check for equality if t and t1 were "float"?

In a different way than above....

>
Or did you have something else in mind for what "equal" means?
>

--
Pietro Cerutti

PGP Public Key:

http://gahr.ch/pgp

[CBFalconer]

Re: compare two float values

neha_chhatre@ya hoo.co.in wrote:

>
actually i want to check wether two float values are equal or not
equal. i.e suppose t and t1 are two float values and i want to
check wether t and t1 are equal or not

#include <float.h /* FLT_EPSILON */
#include <math.h /* fabsf() */

int floatequal(floa t t, float t1) {

float criterion;

criterion = (fabsf(t) + fabsf(t1)) * FLT_EPSILON;
if (fabsf(t - t1) criterion) return 0; /* not equal */
else return 1; /* equal */
} /* untested */

--
[mail]: Chuck F (cbfalconer at maineline dot net)
[page]: <http://cbfalconer.home .att.net>
Try the download section.



--
Posted via a free Usenet account from http://www.teranews.com

[neha_chhatre@yahoo.co.in]

Re: compare two float values

thank you for giving me the site url

[Eric Sosman]

Re: compare two float values

CBFalconer wrote:

neha_chhatre@ya hoo.co.in wrote:

>actually i want to check wether two float values are equal or not
>equal. i.e suppose t and t1 are two float values and i want to
>check wether t and t1 are equal or not

>
#include <float.h /* FLT_EPSILON */
#include <math.h /* fabsf() */
>
int floatequal(floa t t, float t1) {
>
float criterion;
>
criterion = (fabsf(t) + fabsf(t1)) * FLT_EPSILON;
if (fabsf(t - t1) criterion) return 0; /* not equal */
else return 1; /* equal */
} /* untested */

Needs a little more work for NaNs and infinities ...

More to the point, the choice of a proper epsilon is
not dictated solely by the machine's precision, but also
by the computations that produced the numbers. For example,
if you calculate a binomial coefficient as

exp(lgamma(n)-lgamma(m)-lgamma(n-m))*n/(m*(n-m))

.... the accuracy of the result will quite likely depend a
good deal on the accuracies of the four transcendental
function evaluations, as well as on the fundamental precision
of the floating-point representation. An "approximat ely
equal" comparison based solely on the machine's epsilon might
lead one to conclude that the number five-card poker hands
(52 choose 5 == 52!/(5!*47!) == 2598960) is not an integer!

--
Eric.Sosman@sun .com

[user923005]

Re: compare two float values

On Feb 20, 6:42 am, neha_chha...@ya hoo.co.in wrote:

can anybody tell me how to compare two float values
say for example
t and check are two variables declared float how to compare t and
check
please help me as soon as possible

This should be a FAQ.

#include <float.h>
#include <math.h>

int double_compare (double d1, double d2)
{
if (d1 d2)
if ((d1 - d2) < fabs (d1 * DBL_EPSILON))
return 0;
else
return 1;
if (d1 < d2)
if ((d2 - d1) < fabs (d2 * DBL_EPSILON))
return 0;
else
return -1;
return 0;
}

int float_compare (float d1, float d2)
{
if (d1 d2)
if ((d1 - d2) < fabsf (d1 * FLT_EPSILON))
return 0;
else
return 1;
if (d1 < d2)
if ((d2 - d1) < fabsf (d2 * FLT_EPSILON))
return 0;
else
return -1;
return 0;
}

#ifdef UNIT_TEST

#include <stdio.h>

int main ()
{
double u = 1.0;
double v = u + 1e-14;
double big = 1.0;
double a = 1.0, b = 0.9999999999999 9999999999999;
printf ("compare(%* g, %*g) = %d.\n", DBL_DIG+2, a, DBL_DIG+2, b,
double_compare (a, b));
a *= -1;
b *= -1;
printf ("compare(%* g, %*g) = %d.\n", DBL_DIG+2, a, DBL_DIG+2, b,
double_compare (a, b));

big *= 1 << 16;
big *= 1 << 16;
big *= 1 << 16;
big *= 1 << 16;


printf ("compare(%* g, %*g) = %d.\n", DBL_DIG+2, u, DBL_DIG+2, v,
double_compare (u, v));


u *= big;
v *= big;

printf ("compare(%* g, %*g) = %d.\n", DBL_DIG+2, u, DBL_DIG+2, v,
double_compare (u, v));

return 0;
}

#endif

[Mark McIntyre]

Re: compare two float values

Kenneth Brody wrote:

>
How would you check for equality if t and t1 were "int"?
Now, how would you check for equality if t and t1 were "float"?

By some different means. Two mathematically identical floats may compare
inequal by obvious methods.

Or did you have something else in mind for what "equal" means?

Doubtful, but he also probably expected the below to print "true".

#include <stdio.h>
#include <math.h>
int main(void)
{
printf("%f %f %s\n",
exp(log(4.444)) , 4.444,
exp(log(4.444)) ==4.444?"true": "false");
return 0;
}

$ ./a.out
4.444000 4.444000 false

--
Mark McIntyre

CLC FAQ <http://c-faq.com/>
CLC readme: <http://www.ungerhu.com/jxh/clc.welcome.txt >

[CBFalconer]

Re: compare two float values

user923005 wrote:

neha_chha...@ya hoo.co.in wrote:
>

>can anybody tell me how to compare two float values, say for
>example t and check are two variables declared float how to
>compare t and check

>
This should be a FAQ.
>
#include <float.h>
#include <math.h>
>
int double_compare (double d1, double d2)
{
if (d1 d2)
if ((d1 - d2) < fabs (d1 * DBL_EPSILON))
return 0;
else
return 1;
if (d1 < d2)
if ((d2 - d1) < fabs (d2 * DBL_EPSILON))
return 0;
else
return -1;
return 0;
}

What if d1 == DBL_EPSILON and d2 == -LARGE_NUMBER? I think you are
trying to do too much in one routine. I also think I have the
foul-up condition fouled. :-)

--
[mail]: Chuck F (cbfalconer at maineline dot net)
[page]: <http://cbfalconer.home .att.net>
Try the download section.



--
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