shekar b.c wrote:
> Hi all
>
> Give a very good method to count the number of ones in a 32 bit
> number. (caution: looping through testing each bit is not a solution).
>
> regards
A fast way to do it is like this (warning, I don't have time to compile
and run it, there might be little errors):
int nrBits[256];
void Fill_nrBits()
{
for (int i=0; i<256; ++i)
{
int countBits=0;
int n=i;
for (int bit=0; bit<8; ++bit)
{
if ((n&1)==1)
++countBits;
n >>= 1;
}
nrBits[i] = countBits;
}
}
int GetNrBits(int n)
{
unsigned char *c = (unsigned char*)&n;
return nrBits[c[0]] + nrBits[c[1]] + nrBits[c[2]] + nrBits[c[3]];
}
int main()
{
Fill_nrBits();
int n = 12345;
int m = GetNrBits(n);
}
--
Mark Van Peteghem
http://www.q-mentum.com -- easier and more powerful unit testing
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