[algogeeks] Some bit manipulation help

2011-08-28 Thread Nikhil Gupta 
Here is a small piece of program which counts the number of bits set in a
number. I found it online somewhere.
InputOutput00(000)52(101)73(111)

  *int* CountBits (*unsigned* *int* x )
  {
  *static* *unsigned* *int* mask[] *=* { 0x,
  0x,
  0x0F0F0F0F,
  0x00FF00FF,
  0x  } ;
  *int* i ;
  *int* shift ; /* Number of positions to shift to right*/
 *for* ( i *=*0, shift *=*1; i ** 5; i *++*, shift **=* 2)
  x *=* (x ** mask[i ])*+* ( ( x ** shift) ** mask[i]);
  *return* x;
  }

Can anyone explain how this is working?

-- 
Nikhil Gupta
Senior Co-ordinator, Publicity
CSI, NSIT Students' Branch
NSIT, New Delhi, India

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Re: [algogeeks] Some bit manipulation help

2011-08-28 Thread Debabrata Das 
Another approach!!

while(x)
{
x=x(x-1);
count++;
}

On Sun, Aug 28, 2011 at 2:26 PM, Nikhil Gupta nikhilgupta2...@gmail.comwrote:

 Here is a small piece of program which counts the number of bits set in a
 number. I found it online somewhere.
 InputOutput00(000)52(101)73(111)

   *int* CountBits (*unsigned* *int* x )

   {
   *static* *unsigned* *int* mask[] *=* { 0x,

   0x,
   0x0F0F0F0F,
   0x00FF00FF,

   0x  } ;
   *int* i ;
   *int* shift ; /* Number of positions to shift to right*/  
 *for* ( i *=*0, shift *=*1; i ** 5; i *++*, shift **=* 2)

   x *=* (x ** mask[i ])*+* ( ( x ** shift) ** mask[i]);

   *return* x;
   }

 Can anyone explain how this is working?

 --
 Nikhil Gupta
 Senior Co-ordinator, Publicity
 CSI, NSIT Students' Branch
 NSIT, New Delhi, India

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Re: [algogeeks] Some bit manipulation help

2011-08-28 Thread Dheeraj Sharma 
yeah..dat we all know..bt wat actually this code is doing..this is wat am
thinking!!!

On Sun, Aug 28, 2011 at 2:12 AM, Debabrata Das 
debabrata.barunhal...@gmail.com wrote:

 Another approach!!

 while(x)
 {
 x=x(x-1);
 count++;

 }

 On Sun, Aug 28, 2011 at 2:26 PM, Nikhil Gupta 
 nikhilgupta2...@gmail.comwrote:

 Here is a small piece of program which counts the number of bits set in a
 number. I found it online somewhere.
  InputOutput00(000)52(101)73(111)

   *int* CountBits (*unsigned* *int* x )


   {
   *static* *unsigned* *int* mask[] *=* { 0x,


   0x,
   0x0F0F0F0F,
   0x00FF00FF,


   0x  } ;
   *int* i ;
   *int* shift ; /* Number of positions to shift to right*/  
 *for* ( i *=*0, shift *=*1; i ** 5; i *++*, shift **=* 2)


   x *=* (x ** mask[i ])*+* ( ( x ** shift) ** mask[i]);


   *return* x;
   }

 Can anyone explain how this is working?

 --
 Nikhil Gupta
 Senior Co-ordinator, Publicity
 CSI, NSIT Students' Branch
 NSIT, New Delhi, India

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-- 
*Dheeraj Sharma*
Comp Engg.
NIT Kurukshetra
+91 8950264227

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Re: [algogeeks] Some bit manipulation help

2011-08-28 Thread muthu raj 
Can anyone explain logic of  the above code ?
*Muthuraj R
IV th Year , ISE
PESIT , Bangalore*



On Sun, Aug 28, 2011 at 2:16 AM, Dheeraj Sharma dheerajsharma1...@gmail.com
 wrote:

 yeah..dat we all know..bt wat actually this code is doing..this is wat am
 thinking!!!


 On Sun, Aug 28, 2011 at 2:12 AM, Debabrata Das 
 debabrata.barunhal...@gmail.com wrote:

 Another approach!!

 while(x)
 {
 x=x(x-1);
 count++;

 }

 On Sun, Aug 28, 2011 at 2:26 PM, Nikhil Gupta 
 nikhilgupta2...@gmail.comwrote:

 Here is a small piece of program which counts the number of bits set in a
 number. I found it online somewhere.
  InputOutput00(000)52(101)73(111)

   *int* CountBits (*unsigned* *int* x )




   {
   *static* *unsigned* *int* mask[] *=* { 0x,




   0x,
   0x0F0F0F0F,
   0x00FF00FF,




   0x  } ;
   *int* i ;
   *int* shift ; /* Number of positions to shift to right*/  
 *for* ( i *=*0, shift *=*1; i ** 5; i *++*, shift **=* 2)




   x *=* (x ** mask[i ])*+* ( ( x ** shift) ** mask[i]);




   *return* x;
   }

 Can anyone explain how this is working?

 --
 Nikhil Gupta
 Senior Co-ordinator, Publicity
 CSI, NSIT Students' Branch
 NSIT, New Delhi, India

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 --
 *Dheeraj Sharma*
 Comp Engg.
 NIT Kurukshetra
 +91 8950264227


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