Bitwise manipulation

[Nehil]

how can u find whether a no has consecutive zero bits either in from
LSB or MSB.
if they exist in between, then what to do? plz clarify.

 

[Malcolm McLean]

how can u find whether a no has consecutive zero bits either in from
LSB or MSB.
if they exist in between, then what to do? plz clarify.

Take the binary complement of the number (~). Take two copies, and shift one
a bit (<<). Then AND (&, just one). If the answer is non-zero, you have
consecutive zero bits.

 

[Nehil]

Take the binary complement of the number (~). Take two copies, and shift one
a bit (<<). Then AND (&, just one). If the answer is non-zero, you have
consecutive zero bits.

Thanks for your answer. but the solution you suggested only tells true
or false, whether consecutive zero bits are there or not.

i need something different :
i want to know how many consecutive zero bits are there?
for exapmle :
let say arr[0] = 10; so bit representation will be (32-bit)

00000000 00000000 00000000 00001010

so answer should be => 29 from MSB and 1 from LSB.
please clarify.
Thanks.

 

[Eric Sosman]

how can u find whether a no has consecutive zero bits either in from
LSB or MSB.
if they exist in between, then what to do? plz clarify.

Are you the same "Nehil" who is undertaking to write
a garbage collector for C? If so, have you ever heard the
advice "Walk before you run?"

Yes, we all know that "A man's reach should exceed his
grasp," but perhaps by not quite so wide a span ...

 

[Nehil]

Are you the same "Nehil" who is undertaking to write
a garbage collector for C? If so, have you ever heard the
advice "Walk before you run?"

Yes, we all know that "A man's reach should exceed his
grasp," but perhaps by not quite so wide a span ...

===================================================================
Yes, i'm the same Nehil. but i could not understand your wordings.
i
came to this doubt in that project only. i designed a bitmap for each
page i allocate, and now want to know how many pages have been
allocated by knowing how many bits are there zero??

is this approach good?

 

[pete]

Take the binary complement of the number (~). Take two copies, and shift one
a bit (<<). Then AND (&, just one). If the answer is non-zero, you have
consecutive zero bits.

Thanks for your answer. but the solution you suggested only tells true
or false, whether consecutive zero bits are there or not.

i need something different :
i want to know how many consecutive zero bits are there?
for exapmle :
let say arr[0] = 10; so bit representation will be (32-bit)

00000000 00000000 00000000 00001010

so answer should be => 29 from MSB and 1 from LSB.
please clarify.

/* BEGIN new.c */

#include <stdio.h>

#define N 10U
#define str(s) # s
#define xstr(s) str(s)

void consecutive_zero_bits(unsigned n, unsigned *most, unsigned *least);

int main(void)
{
unsigned most, least;

consecutive_zero_bits(N, &most, &least);
puts(xstr(N));
printf("%u from MSB and %u from LSB.\n", most, least);
return 0;
}

void consecutive_zero_bits(unsigned n, unsigned *most, unsigned *least)
{
unsigned mask, count;

count = 0;
for (mask = 1; mask != 0; mask *= 2) {
if( (mask & n) == 0) {
++count;
} else {
*least = count;
break;
}
}
count = 0;
for (mask = (0u - 1) / 2 + 1; mask != 0; mask /= 2) {
if( (mask & n) == 0) {
++count;
} else {
*most = count;
break;
}
}
}

/* END new.c */

 

[Malcolm McLean]

===================================================================
Yes, i'm the same Nehil. but i could not understand your wordings.
i
came to this doubt in that project only. i designed a bitmap for each
page i allocate, and now want to know how many pages have been
allocated by knowing how many bits are there zero??

is this approach good?

A garbage collector, let alone an efficient garbage collector, is a very
difficult routine to write. If you can't even do basic bit manipulation - no
shame on you, we were all beginners at some time - then there is no way you
are going to achieve a garbage collector, except by some miracle.

 

[Nehil]

A garbage collector, let alone an efficient garbage collector, is a very
difficult routine to write. If you can't even do basic bit manipulation - no
shame on you, we were all beginners at some time - then there is no way you
are going to achieve a garbage collector, except by some miracle.

Thanks all for your answers and suggestions.
However i've developed it myself and it is working efficiently. it was
bit manipulation that makes me nervous while thinking logic for it.
but i'll practice for it.

the allocator and de-allocator both r working fine.
Actually, the problem i asked to find some effecient solution for it.
by linear searching, i'd already done it.

thnkas all.

 

[Thad Smith]

how can u find whether a no has consecutive zero bits either in from
LSB or MSB.

What does "either in from LSB or MSB" mean?

if they exist in between, then what to do?

Between what?

> plz clarify.

I suggest that _you_ clarify.