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What is the most efficient way to count the number of bits which are set in an integer?
What is the most efficient way to count the number of bits which are set in an integer?
✍: Guest
Many ``bit-fiddling'' problems like this one can be sped up and streamlined using lookup tables (but see question 20.13). Here is a little function which computes the number of bits in a value, 4 bits at a time:
static int bitcounts[] =
{0, 1, 1, 2, 1, 2, 2, 3, 1, 2, 2, 3, 2, 3, 3, 4};
int bitcount(unsigned int u)
{
int n = 0;
for(; u != 0; u >>= 4)
n += bitcounts[u & 0x0f];
return n;
}
2015-02-11, 1120👍, 0💬
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