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]

Re: About very long Bit-numbers (bitfields?)

Juha Kettunen <not@valid.co m> spoke thus:
[color=blue]
> 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:[/color]

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]

Re: About very long Bit-numbers (bitfields?)

Juha Kettunen <not@valid.co m> spoke thus:
[color=blue]
> 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:[/color]

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]

Re: About very long Bit-numbers (bitfields?)

On Fri, 9 Apr 2004 10:33:24 +0100, "Juha Kettunen" <not@valid.co m> wrote:
[color=blue]
>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;[/color]

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.
[color=blue]
>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:[/color]

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:

https://www.bdsoft.com/tools/stlfilt.html

[Leor Zolman]

Re: About very long Bit-numbers (bitfields?)

On Fri, 9 Apr 2004 10:33:24 +0100, "Juha Kettunen" <not@valid.co m> wrote:
[color=blue]
>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;[/color]

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.
[color=blue]
>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:[/color]

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:

https://www.bdsoft.com/tools/stlfilt.html

[Juha Kettunen]

Re: About very long Bit-numbers (bitfields?)

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" <leor@bdsoft.co m> wrote in message
news:fkrd70l8e9 ip1bc2qbfg6snq0 a0fau8e62@4ax.c om...[color=blue]
> On Fri, 9 Apr 2004 10:33:24 +0100, "Juha Kettunen" <not@valid.co m> wrote:
>[color=green]
> >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;[/color]
>
> 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.
>[color=green]
> >How about if I want to get for example a 640 bit long *one* number (say[/color][/color]
b)[color=blue][color=green]
> >and do the same binary operations to it (b |= 128)? I haven't found[/color][/color]
answer[color=blue][color=green]
> >for this ... do I need to use Bitfields:[/color]
>
> 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[/color]

[Juha Kettunen]

Re: About very long Bit-numbers (bitfields?)

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" <leor@bdsoft.co m> wrote in message
news:fkrd70l8e9 ip1bc2qbfg6snq0 a0fau8e62@4ax.c om...[color=blue]
> On Fri, 9 Apr 2004 10:33:24 +0100, "Juha Kettunen" <not@valid.co m> wrote:
>[color=green]
> >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;[/color]
>
> 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.
>[color=green]
> >How about if I want to get for example a 640 bit long *one* number (say[/color][/color]
b)[color=blue][color=green]
> >and do the same binary operations to it (b |= 128)? I haven't found[/color][/color]
answer[color=blue][color=green]
> >for this ... do I need to use Bitfields:[/color]
>
> 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[/color]

[Juha Kettunen]

Re: About very long Bit-numbers (bitfields?)


"Christophe r Benson-Manica" <ataru@nospam.c yberspace.org> wrote in message
news:c56ql7$1s8 $1@chessie.cirr .com...[color=blue]
> Juha Kettunen <not@valid.co m> spoke thus:
>[color=green]
> > How about if I want to get for example a 640 bit long *one* number (say[/color][/color]
b)[color=blue][color=green]
> > and do the same binary operations to it (b |= 128)? I haven't found[/color][/color]
answer[color=blue][color=green]
> > for this ... do I need to use Bitfields:[/color]
>
> You might look at vector<bool>, although I have no idea how useful
> you'll find it.
>[/color]

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]

Re: About very long Bit-numbers (bitfields?)


"Christophe r Benson-Manica" <ataru@nospam.c yberspace.org> wrote in message
news:c56ql7$1s8 $1@chessie.cirr .com...[color=blue]
> Juha Kettunen <not@valid.co m> spoke thus:
>[color=green]
> > How about if I want to get for example a 640 bit long *one* number (say[/color][/color]
b)[color=blue][color=green]
> > and do the same binary operations to it (b |= 128)? I haven't found[/color][/color]
answer[color=blue][color=green]
> > for this ... do I need to use Bitfields:[/color]
>
> You might look at vector<bool>, although I have no idea how useful
> you'll find it.
>[/color]

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]

Re: About very long Bit-numbers (bitfields?)

On Fri, 9 Apr 2004 13:35:19 +0100, "Juha Kettunen" <not@valid.co m> wrote:
[color=blue]
>
>"Christophe r Benson-Manica" <ataru@nospam.c yberspace.org> wrote in message
>news:c56ql7$1s 8$1@chessie.cir r.com...[color=green]
>> Juha Kettunen <not@valid.co m> spoke thus:
>>[color=darkred]
>> > How about if I want to get for example a 640 bit long *one* number (say[/color][/color]
>b)[color=green][color=darkred]
>> > and do the same binary operations to it (b |= 128)? I haven't found[/color][/color]
>answer[color=green][color=darkred]
>> > for this ... do I need to use Bitfields:[/color]
>>
>> You might look at vector<bool>, although I have no idea how useful
>> you'll find it.
>>[/color]
>
>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.
>[/color]

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:

https://www.bdsoft.com/tools/stlfilt.html

[Leor Zolman]

Re: About very long Bit-numbers (bitfields?)

On Fri, 9 Apr 2004 13:35:19 +0100, "Juha Kettunen" <not@valid.co m> wrote:
[color=blue]
>
>"Christophe r Benson-Manica" <ataru@nospam.c yberspace.org> wrote in message
>news:c56ql7$1s 8$1@chessie.cir r.com...[color=green]
>> Juha Kettunen <not@valid.co m> spoke thus:
>>[color=darkred]
>> > How about if I want to get for example a 640 bit long *one* number (say[/color][/color]
>b)[color=green][color=darkred]
>> > and do the same binary operations to it (b |= 128)? I haven't found[/color][/color]
>answer[color=green][color=darkred]
>> > for this ... do I need to use Bitfields:[/color]
>>
>> You might look at vector<bool>, although I have no idea how useful
>> you'll find it.
>>[/color]
>
>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.
>[/color]

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:

https://www.bdsoft.com/tools/stlfilt.html

[Juha Kettunen]

Re: About very long Bit-numbers (bitfields?)


"Leor Zolman" <leor@bdsoft.co m> wrote in message
news:ad2e70huvn 4hk6r67abr1so6m 6jlt7o0o6@4ax.c om...[color=blue]
> On Fri, 9 Apr 2004 13:35:19 +0100, "Juha Kettunen" <not@valid.co m> wrote:
>
> 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[/color]
without[color=blue]
> 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[/color]

Now I tried that bitset, and ... hmmm.. there is one "problem": it is too
slow! I need to have very fast calculations, and normal bit operations with
integers does that, but it seems to me that bitset is slow. I did two tests:

1.
bitset<31> a;

for (int i=1;i<40000000; i++)
{
a |= (11 << 10);
}


2.
unsigned long f;

for (int i=1;i<40000000; i++)
{
f |= (11 << 10);
}

The first one took about 10 seconds to complete, but the second one
basically 0 seconds!

bitset does the job, but is too slow.

Is there a way to do it fast (basically I mean that if you use bitset<300>
a;)?

[Juha Kettunen]

Re: About very long Bit-numbers (bitfields?)


"Leor Zolman" <leor@bdsoft.co m> wrote in message
news:ad2e70huvn 4hk6r67abr1so6m 6jlt7o0o6@4ax.c om...[color=blue]
> On Fri, 9 Apr 2004 13:35:19 +0100, "Juha Kettunen" <not@valid.co m> wrote:
>
> 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[/color]
without[color=blue]
> 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[/color]

Now I tried that bitset, and ... hmmm.. there is one "problem": it is too
slow! I need to have very fast calculations, and normal bit operations with
integers does that, but it seems to me that bitset is slow. I did two tests:

1.
bitset<31> a;

for (int i=1;i<40000000; i++)
{
a |= (11 << 10);
}


2.
unsigned long f;

for (int i=1;i<40000000; i++)
{
f |= (11 << 10);
}

The first one took about 10 seconds to complete, but the second one
basically 0 seconds!

bitset does the job, but is too slow.

Is there a way to do it fast (basically I mean that if you use bitset<300>
a;)?

[Julie]

Re: About very long Bit-numbers (bitfields?)

Juha Kettunen wrote:[color=blue]
>
> "Leor Zolman" <leor@bdsoft.co m> wrote in message
> news:ad2e70huvn 4hk6r67abr1so6m 6jlt7o0o6@4ax.c om...[color=green]
> > On Fri, 9 Apr 2004 13:35:19 +0100, "Juha Kettunen" <not@valid.co m> wrote:
> >
> > 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[/color]
> without[color=green]
> > 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[/color]
>
> Now I tried that bitset, and ... hmmm.. there is one "problem": it is too
> slow! I need to have very fast calculations, and normal bit operations with
> integers does that, but it seems to me that bitset is slow. I did two tests:
>
> 1.
> bitset<31> a;
>
> for (int i=1;i<40000000; i++)
> {
> a |= (11 << 10);
> }
>
> 2.
> unsigned long f;
>
> for (int i=1;i<40000000; i++)
> {
> f |= (11 << 10);
> }
>
> The first one took about 10 seconds to complete, but the second one
> basically 0 seconds!
>
> bitset does the job, but is too slow.
>
> Is there a way to do it fast (basically I mean that if you use bitset<300>
> a;)?[/color]

Careful there -- did you examine the executable code for loop 2? As far as I
know, it isn't unreasonable to expect an optimizing compiler to reduce that to
a single statement since the loop operand is constant.

Recreate your test using an operand that isn't constant, verify the executable
code, and re-run the test.

[Julie]

Re: About very long Bit-numbers (bitfields?)

Juha Kettunen wrote:[color=blue]
>
> "Leor Zolman" <leor@bdsoft.co m> wrote in message
> news:ad2e70huvn 4hk6r67abr1so6m 6jlt7o0o6@4ax.c om...[color=green]
> > On Fri, 9 Apr 2004 13:35:19 +0100, "Juha Kettunen" <not@valid.co m> wrote:
> >
> > 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[/color]
> without[color=green]
> > 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[/color]
>
> Now I tried that bitset, and ... hmmm.. there is one "problem": it is too
> slow! I need to have very fast calculations, and normal bit operations with
> integers does that, but it seems to me that bitset is slow. I did two tests:
>
> 1.
> bitset<31> a;
>
> for (int i=1;i<40000000; i++)
> {
> a |= (11 << 10);
> }
>
> 2.
> unsigned long f;
>
> for (int i=1;i<40000000; i++)
> {
> f |= (11 << 10);
> }
>
> The first one took about 10 seconds to complete, but the second one
> basically 0 seconds!
>
> bitset does the job, but is too slow.
>
> Is there a way to do it fast (basically I mean that if you use bitset<300>
> a;)?[/color]

Careful there -- did you examine the executable code for loop 2? As far as I
know, it isn't unreasonable to expect an optimizing compiler to reduce that to
a single statement since the loop operand is constant.

Recreate your test using an operand that isn't constant, verify the executable
code, and re-run the test.