Convert infinity to zero

[horacius.rex]

Hi,

I have a code that in some part of the program calculates 1/x for a
lot of different x's. About 1 of 100 times x is equal to zero, so when
I print the result I obtain inf. I wonder if there is a way to detect
this "infinity" and convert it to the float zero. I mean something
like

for i = ....
calculate 1/x_i
if x_i = inf then x_i = 0.
....
Thanks

[horacius.rex]

On 16 mayo, 23:26, gaze...@xmissio n.xmission.com (Kenny McCormack)
wrote:

In article <1179345346.304 531.304...@w5g2 000hsg.googlegr oups.com>,

Irish <irish....@gmai l.comwrote:

On May 16, 12:10 pm, horacius....@gm ail.com wrote:

Hi,

I have a code that in some part of the program calculates 1/x for a
lot of different x's. About 1 of 100 times x is equal to zero, so when
I print the result I obtain inf. I wonder if there is a way to detect
this "infinity" and convert it to the float zero. I mean something
like

for i = ....
calculate 1/x_i
if x_i = inf then x_i = 0.
....

Thanks

Maybe I'm missing something, but if x or x[i] is equal to zero at some
point, I think you should handle that as soon as you know its value
rather than after you divide by it and save yourself (and your CPU)
the trouble of obtaining a value you're going to throw away/replace
with zero.

for(i=...)
if(x[i] == 0) ... // set value to zero
else ... // set value to 1/x[i]
...

Like Tim said, some actual code might help.

But, as always, that's the problem with "simplifyin g your code down to
the smallest, compilable example that demonstrates the problem" (as we
all urge the newbies to do).

See, the actual thing that they are trying to learn is how to handle
errors. So, as we urge them to do, they simplify it down before
posting, then we (wrongly) try to solve their "problem as posted" -
i.e., don't cause the error in the first place - which bears no
relevance to their actual issue (what they are actually trying to teach
themselves).

Hi,

my problem is that I have a black-box routine which gives me the
results. So I can not check before anything. I can only work with the
results.

If not, of course that the solution would be obvious and I would fix
the program for not to give the "infinity" result.

So, any of you know how to solve this programming puzzle ? Can you
handle the infinity ? ....

[Kenny McCormack]

In article <11************ **********@n59g 2000hsh.googleg roups.com>,
<ho**********@g mail.comwrote:
....

>Hi,

my problem is that I have a black-box routine which gives me the
results. So I can not check before anything. I can only work with the
results.

Your real problem is that you posted this twice.

>If not, of course that the solution would be obvious and I would fix
the program for not to give the "infinity" result.

So, any of you know how to solve this programming puzzle ? Can you
handle the infinity ? ....

Exactly my point. That your real problem prevented you from doing it
"the easy way". That was the point I was trying to put in front of some
of the other posters.

[Keith Thompson]

ho**********@gm ail.com writes:

On 16 mayo, 23:26, gaze...@xmissio n.xmission.com (Kenny McCormack)
wrote:

>In article <1179345346.304 531.304...@w5g2 000hsg.googlegr oups.com>,
Irish <irish....@gmai l.comwrote:

>On May 16, 12:10 pm, horacius....@gm ail.com wrote:
I have a code that in some part of the program calculates 1/x for a
lot of different x's. About 1 of 100 times x is equal to zero, so when
I print the result I obtain inf. I wonder if there is a way to detect
this "infinity" and convert it to the float zero.

[...]

my problem is that I have a black-box routine which gives me the
results. So I can not check before anything. I can only work with the
results.

If not, of course that the solution would be obvious and I would fix
the program for not to give the "infinity" result.

So, any of you know how to solve this programming puzzle ? Can you
handle the infinity ? ....

The <math.hheader declares a number of classification macros:

fpclassify() yields an int value for a floating-point argument, one of
FP_INFINITE
FP_NAN
FP_NORMAL
FP_SUBNORMAL
FP_ZERO

Other macros, yielding a true or false result, are:
isfinite()
isinf()
isnan()
isnormal()

These are new in C99, so your implementation may or may not support
them. Even if it does, they may or may not work as you want them to;
the standard doesn't require implementations to support NaNs and
Infinities.

If your black-box routine divides by zero internally (and you're not
able to detect this in advance by checking the arguments you feed into
the black box), then strictly speaking it's already invoked undefined
behavior, and you can't reliably do anything about it. But *if* your
implementation supports the classification macros, and *if* a
floating-point division by zero yields Infinity or NaN (NaN for
0.0/0.0, Infinity for nonzero/0.0), then that's probably your best
bet.

Consult your implementation' s documentation to find out how it behaves
on floating-point division by zero and whether it supports the
classification macros.

See also section 7.12.3 of the C99 standard; the latest draft is
available at
<http://www.open-std.org/jtc1/sc22/wg14/www/docs/n1124.pdf>.

--
Keith Thompson (The_Other_Keit h) ks***@mib.org <http://www.ghoti.net/~kst>
San Diego Supercomputer Center <* <http://users.sdsc.edu/~kst>
"We must do something. This is something. Therefore, we must do this."
-- Antony Jay and Jonathan Lynn, "Yes Minister"