By using this site, you agree to our updated Privacy Policy and our Terms of Use. Manage your Cookies Settings.
446,234 Members | 1,941 Online
Bytes IT Community
+ Ask a Question
Need help? Post your question and get tips & solutions from a community of 446,234 IT Pros & Developers. It's quick & easy.

float and 1's

P: n/a
Hi,
Just like counting the number of bits set to
1 in an integral variable, can we count the same
in a float?

I have two solutions in my mind:

1.
union {
float f;
int i;
}u = { 10 };

Now, count the required number from u.i.
Will this work?
2.
float f;
unsigned char uc[sizeof (float)];

memcpy ( uc, &f, sizeof (float) );

Now count from the array. How about this?
Season's Greetings!

--
Vijay Kumar R Zanvar
My Home Page - http://www.geocities.com/vijoeyz/
Nov 14 '05 #1
Share this Question
Share on Google+
5 Replies


P: n/a
"Vijay Kumar R Zanvar" <vi*****@hotpop.com> wrote in message
news:bt************@ID-203837.news.uni-berlin.de...
Hi,
Just like counting the number of bits set to
1 in an integral variable, can we count the same
in a float?

I have two solutions in my mind:

1.
union {
float f;
int i;
}u = { 10 };

Now, count the required number from u.i.
Will this work?
2.
float f;
unsigned char uc[sizeof (float)];

memcpy ( uc, &f, sizeof (float) );

Now count from the array. How about this?
Season's Greetings!

--
Vijay Kumar R Zanvar
My Home Page - http://www.geocities.com/vijoeyz/

Hello,

It is enough to declare the float then take a char* to it as:
float f;
char *p = &f;
// now do the bit counting in 'p' till sizeof(f) , making at most
sizeof(f)*8 bits

--
Elias
Nov 14 '05 #2

P: n/a
lallous wrote:
Hello,

It is enough to declare the float then take a char* to it as:
float f;
char *p = &f;
You need an explicit cast here. And it should be unsigned char*
probably.

unsigned char *p = (unsigned char *)&f;
// now do the bit counting in 'p' till sizeof(f) , making at most
sizeof(f)*8 bits


Note that this will also count any padding bits if there are any.

--
Thomas.

Nov 14 '05 #3

P: n/a
"Vijay Kumar R Zanvar" <vi*****@hotpop.com> writes:
Just like counting the number of bits set to
1 in an integral variable, can we count the same
in a float?

I have two solutions in my mind:

1.
union {
float f;
int i;
}u = { 10 };

Now, count the required number from u.i.
Will this work?
Not reliably. Note that float and int may or may not be the same
size. (As a matter of style, I'd use "10.0", or even "10.0f", rather
than "10" in the initialization to make it clear that you're
initializing the float member.)
2.
float f;
unsigned char uc[sizeof (float)];

memcpy ( uc, &f, sizeof (float) );

Now count from the array. How about this?


Yes, that should work, though others have pointed out that you don't
really need to copy f to an array.

BTW, I can't think of any use for the number of 1 bits in a float
other than idle curiosity -- not that there's anything wrong with idle
curiosity.

--
Keith Thompson (The_Other_Keith) ks***@mib.org <http://www.ghoti.net/~kst>
San Diego Supercomputer Center <*> <http://www.sdsc.edu/~kst>
Schroedinger does Shakespeare: "To be *and* not to be"
(Note new e-mail address)
Nov 14 '05 #4

P: n/a
On Fri, 2 Jan 2004 13:49:15 +0200, "lallous" <la*****@lgwm.org> wrote
in comp.lang.c:
"Vijay Kumar R Zanvar" <vi*****@hotpop.com> wrote in message
news:bt************@ID-203837.news.uni-berlin.de...
Hi,
Just like counting the number of bits set to
1 in an integral variable, can we count the same
in a float?

I have two solutions in my mind:

1.
union {
float f;
int i;
}u = { 10 };

Now, count the required number from u.i.
Will this work?
2.
float f;
unsigned char uc[sizeof (float)];

memcpy ( uc, &f, sizeof (float) );

Now count from the array. How about this?
Season's Greetings!

--
Vijay Kumar R Zanvar
My Home Page - http://www.geocities.com/vijoeyz/

Hello,

It is enough to declare the float then take a char* to it as:
float f;
char *p = &f;
// now do the bit counting in 'p' till sizeof(f) , making at most
sizeof(f)*8 bits


Aside from what others have said, your very last sentence is
completely wrong. I am working on a platform right now where CHAR_BIT
is 16. sizeof(float) is 2, and a float contains 32 bits.

It is definitely possible for the binary representation of a float to
have more than sizeof(float)*8 1 bits. In fact it could have as many
as sizeof(float)*16 1 bits.

But it will never, ever have more than sizeof(float)*CHAR_BIT 1 bits.

--
Jack Klein
Home: http://JK-Technology.Com
FAQs for
comp.lang.c http://www.eskimo.com/~scs/C-faq/top.html
comp.lang.c++ http://www.parashift.com/c++-faq-lite/
alt.comp.lang.learn.c-c++ ftp://snurse-l.org/pub/acllc-c++/faq
Nov 14 '05 #5

P: n/a
[..]

BTW, I can't think of any use for the number of 1 bits in a float
other than idle curiosity -- not that there's anything wrong with idle
curiosity.


You are right. It was only my curiosity.

Thanks
vijay-z.
Nov 14 '05 #6

This discussion thread is closed

Replies have been disabled for this discussion.