About very long Bit-numbers (bitfields?)

[Juha Kettunen]

Hi

I don't know if I am using right words (bit-number), but this is what I
mean:

You can set a 64 bit number:

unsigned long a;

Now you can use binary operators to manipulate variable a (for example
a |= (unsigned long) 128
).

How about if I want to get for example a 640 bit long *one* number (say b)
and do the same binary operations to it (b |= 128)? I haven't found answer
for this ... do I need to use Bitfields:

struct BITS
{
unsigned long b1;
unsigned long b2;
unsigned long b3;
.... (10 times)
};

I don't know ...

[Christopher Benson-Manica]

Juha Kettunen <no*@valid.co m> spoke thus:

How about if I want to get for example a 640 bit long *one* number (say b)
and do the same binary operations to it (b |= 128)? I haven't found answer
for this ... do I need to use Bitfields:

You might look at vector<bool>, although I have no idea how useful
you'll find it.

--
Christopher Benson-Manica | I *should* know what I'm talking about - if I
ataru(at)cybers pace.org | don't, I need to know. Flames welcome.

[Christopher Benson-Manica]

Juha Kettunen <no*@valid.co m> spoke thus:

How about if I want to get for example a 640 bit long *one* number (say b)
and do the same binary operations to it (b |= 128)? I haven't found answer
for this ... do I need to use Bitfields:

You might look at vector<bool>, although I have no idea how useful
you'll find it.

--
Christopher Benson-Manica | I *should* know what I'm talking about - if I
ataru(at)cybers pace.org | don't, I need to know. Flames welcome.

[Leor Zolman]

On Fri, 9 Apr 2004 10:33:24 +0100, "Juha Kettunen" <no*@valid.co m> wrote:

Hi

I don't know if I am using right words (bit-number), but this is what I
mean:

You can set a 64 bit number:

unsigned long a;
Just FYI, the number of bits in a long (unsigned or otherwise) is
platform-dependent. On my system they're only 32 bits. But that doesn't
have much bearing on your real question, which is how to get /real/ long
bit sequences.
How about if I want to get for example a 640 bit long *one* number (say b)
and do the same binary operations to it (b |= 128)? I haven't found answer
for this ... do I need to use Bitfields:

For that, Christopher's suggestion of vector<bool> may be adequate.
vector<bool> is the "black sheep" of the STL container family...becaus e it
doesn't meet all the usual vector requirements:

#include <vector>

int main()
{
std::vector<cha r> vc;
std::vector<boo l> vb;

vc.push_back('x ');
vc.push_back('y ');
vb.push_back(tr ue);
vb.push_back(tr ue);

std::vector<cha r>::iterator vcit = vc.begin();
std::vector<boo l>::iterator vbit = vb.begin();

*vcit = 'z'; // OK
*vbit = false; // OK

char *cp = &vc[0]; // OK
bool *bp = &vb[0]; // Oops: won't compile.

return 0;
}

On the other hand, it provides some operation specialized for bits that
std::vector<som ething-other-than-bool> does not. Josuttis 6.2.6 has the
gory details. If you can avoid the potholes, it may work fine for you.
-leor

--
Leor Zolman --- BD Software --- www.bdsoft.com
On-Site Training in C/C++, Java, Perl and Unix
C++ users: Download BD Software's free STL Error Message Decryptor at:
www.bdsoft.com/tools/stlfilt.html

[Leor Zolman]

On Fri, 9 Apr 2004 10:33:24 +0100, "Juha Kettunen" <no*@valid.co m> wrote:

Hi

I don't know if I am using right words (bit-number), but this is what I
mean:

You can set a 64 bit number:

unsigned long a;
Just FYI, the number of bits in a long (unsigned or otherwise) is
platform-dependent. On my system they're only 32 bits. But that doesn't
have much bearing on your real question, which is how to get /real/ long
bit sequences.
How about if I want to get for example a 640 bit long *one* number (say b)
and do the same binary operations to it (b |= 128)? I haven't found answer
for this ... do I need to use Bitfields:

For that, Christopher's suggestion of vector<bool> may be adequate.
vector<bool> is the "black sheep" of the STL container family...becaus e it
doesn't meet all the usual vector requirements:

#include <vector>

int main()
{
std::vector<cha r> vc;
std::vector<boo l> vb;

vc.push_back('x ');
vc.push_back('y ');
vb.push_back(tr ue);
vb.push_back(tr ue);

std::vector<cha r>::iterator vcit = vc.begin();
std::vector<boo l>::iterator vbit = vb.begin();

*vcit = 'z'; // OK
*vbit = false; // OK

char *cp = &vc[0]; // OK
bool *bp = &vb[0]; // Oops: won't compile.

return 0;
}

On the other hand, it provides some operation specialized for bits that
std::vector<som ething-other-than-bool> does not. Josuttis 6.2.6 has the
gory details. If you can avoid the potholes, it may work fine for you.
-leor

--
Leor Zolman --- BD Software --- www.bdsoft.com
On-Site Training in C/C++, Java, Perl and Unix
C++ users: Download BD Software's free STL Error Message Decryptor at:
www.bdsoft.com/tools/stlfilt.html

[Juha Kettunen]

ok , thanks for you and Christopher. I will check that vector<bool>.

Hmm but I think cannot do bit operations for it:

vector<bool> a;

a |= 128;

The main point is, that I really need to be able to do similar operations
than bit operations to get some benefit in my code (That means, that set
*many* bits at the same time, as b |= 128 does). But maybe I can do it with
that vector ....

But anyway, it seems to be second best (better than normal arrays) if I
cannot use bit operations...

"Leor Zolman" <le**@bdsoft.co m> wrote in message
news:fk******** *************** *********@4ax.c om...

On Fri, 9 Apr 2004 10:33:24 +0100, "Juha Kettunen" <no*@valid.co m> wrote:

Hi

I don't know if I am using right words (bit-number), but this is what I
mean:

You can set a 64 bit number:

unsigned long a;

Just FYI, the number of bits in a long (unsigned or otherwise) is
platform-dependent. On my system they're only 32 bits. But that doesn't
have much bearing on your real question, which is how to get /real/ long
bit sequences.

How about if I want to get for example a 640 bit long *one* number (say b)and do the same binary operations to it (b |= 128)? I haven't found answerfor this ... do I need to use Bitfields:

For that, Christopher's suggestion of vector<bool> may be adequate.
vector<bool> is the "black sheep" of the STL container family...becaus e it
doesn't meet all the usual vector requirements:

#include <vector>

int main()
{
std::vector<cha r> vc;
std::vector<boo l> vb;

vc.push_back('x ');
vc.push_back('y ');
vb.push_back(tr ue);
vb.push_back(tr ue);

std::vector<cha r>::iterator vcit = vc.begin();
std::vector<boo l>::iterator vbit = vb.begin();

*vcit = 'z'; // OK
*vbit = false; // OK

char *cp = &vc[0]; // OK
bool *bp = &vb[0]; // Oops: won't compile.

return 0;
}

On the other hand, it provides some operation specialized for bits that
std::vector<som ething-other-than-bool> does not. Josuttis 6.2.6 has the
gory details. If you can avoid the potholes, it may work fine for you.
-leor

--
Leor Zolman --- BD Software --- www.bdsoft.com
On-Site Training in C/C++, Java, Perl and Unix
C++ users: Download BD Software's free STL Error Message Decryptor at:
www.bdsoft.com/tools/stlfilt.html

[Juha Kettunen]

ok , thanks for you and Christopher. I will check that vector<bool>.

Hmm but I think cannot do bit operations for it:

vector<bool> a;

a |= 128;

The main point is, that I really need to be able to do similar operations
than bit operations to get some benefit in my code (That means, that set
*many* bits at the same time, as b |= 128 does). But maybe I can do it with
that vector ....

But anyway, it seems to be second best (better than normal arrays) if I
cannot use bit operations...

"Leor Zolman" <le**@bdsoft.co m> wrote in message
news:fk******** *************** *********@4ax.c om...

On Fri, 9 Apr 2004 10:33:24 +0100, "Juha Kettunen" <no*@valid.co m> wrote:

Hi

I don't know if I am using right words (bit-number), but this is what I
mean:

You can set a 64 bit number:

unsigned long a;

Just FYI, the number of bits in a long (unsigned or otherwise) is
platform-dependent. On my system they're only 32 bits. But that doesn't
have much bearing on your real question, which is how to get /real/ long
bit sequences.

How about if I want to get for example a 640 bit long *one* number (say b)and do the same binary operations to it (b |= 128)? I haven't found answerfor this ... do I need to use Bitfields:

For that, Christopher's suggestion of vector<bool> may be adequate.
vector<bool> is the "black sheep" of the STL container family...becaus e it
doesn't meet all the usual vector requirements:

#include <vector>

int main()
{
std::vector<cha r> vc;
std::vector<boo l> vb;

vc.push_back('x ');
vc.push_back('y ');
vb.push_back(tr ue);
vb.push_back(tr ue);

std::vector<cha r>::iterator vcit = vc.begin();
std::vector<boo l>::iterator vbit = vb.begin();

*vcit = 'z'; // OK
*vbit = false; // OK

char *cp = &vc[0]; // OK
bool *bp = &vb[0]; // Oops: won't compile.

return 0;
}

On the other hand, it provides some operation specialized for bits that
std::vector<som ething-other-than-bool> does not. Josuttis 6.2.6 has the
gory details. If you can avoid the potholes, it may work fine for you.
-leor

--
Leor Zolman --- BD Software --- www.bdsoft.com
On-Site Training in C/C++, Java, Perl and Unix
C++ users: Download BD Software's free STL Error Message Decryptor at:
www.bdsoft.com/tools/stlfilt.html

[Juha Kettunen]

"Christophe r Benson-Manica" <at***@nospam.c yberspace.org> wrote in message
news:c5******** **@chessie.cirr .com...

Juha Kettunen <no*@valid.co m> spoke thus:

How about if I want to get for example a 640 bit long *one* number (say b) and do the same binary operations to it (b |= 128)? I haven't found answer for this ... do I need to use Bitfields:

You might look at vector<bool>, although I have no idea how useful
you'll find it.

Actually, when I was checking from the "Stroustrup C++" this vector issue
just now, I recognized, that there is a std::bitset vector type as well,
which is definetely most suitable for me: It handles binary values and have
all of those bit operations |=, &=, and so on.

But thanks, i didnt really even think that vectors could solve my problem
.... (I thought i must be a struct).

I will try it now, and see if it *really* works :)...

[Juha Kettunen]

"Christophe r Benson-Manica" <at***@nospam.c yberspace.org> wrote in message
news:c5******** **@chessie.cirr .com...

Juha Kettunen <no*@valid.co m> spoke thus:

How about if I want to get for example a 640 bit long *one* number (say b) and do the same binary operations to it (b |= 128)? I haven't found answer for this ... do I need to use Bitfields:

You might look at vector<bool>, although I have no idea how useful
you'll find it.

Actually, when I was checking from the "Stroustrup C++" this vector issue
just now, I recognized, that there is a std::bitset vector type as well,
which is definetely most suitable for me: It handles binary values and have
all of those bit operations |=, &=, and so on.

But thanks, i didnt really even think that vectors could solve my problem
.... (I thought i must be a struct).

I will try it now, and see if it *really* works :)...

[Leor Zolman]

On Fri, 9 Apr 2004 13:35:19 +0100, "Juha Kettunen" <no*@valid.co m> wrote:

"Christophe r Benson-Manica" <at***@nospam.c yberspace.org> wrote in message
news:c5******* ***@chessie.cir r.com...

Juha Kettunen <no*@valid.co m> spoke thus:

> How about if I want to get for example a 640 bit long *one* number (sayb) > and do the same binary operations to it (b |= 128)? I haven't foundanswer > for this ... do I need to use Bitfields:

You might look at vector<bool>, although I have no idea how useful
you'll find it.

Actually, when I was checking from the "Stroustrup C++" this vector issue
just now, I recognized, that there is a std::bitset vector type as well,
which is definetely most suitable for me: It handles binary values and have
all of those bit operations |=, &=, and so on.

Yes, that's clearly a better starting point, and I'm kicking myself for
having forgotten about std::bitset. So as not to depart this thread without
having at least /something/ helpful to say, let me recommend that you get
yourself a copy of Josuttis' "The C++ Standard Library". It is
indispensable when trying to choose and then use STL facilities... and it
has ten pages on bitset.
-leor

--
Leor Zolman --- BD Software --- www.bdsoft.com
On-Site Training in C/C++, Java, Perl and Unix
C++ users: Download BD Software's free STL Error Message Decryptor at:
www.bdsoft.com/tools/stlfilt.html