count of bits set in a long

[Kevin D. Quitt]

In article <Mazyneu00WB6EAjWo8 at andrew.cmu.edu> sa1z+ at andrew.cmu.edu (Sudheer Apte) writes:
>I was thinking along these lines:
>
>static int num_bits[256] = {0, 1, 1, 2, 1, ... /* etc. */ };
>
>struct four_pack { char a; char b; char c; char d;};
>
>int bit_count(i)
>unsigned long i;
>{
>	struct four_pack f;
>	f = (struct four_pack) i;
>	return num_bits[f.a] + num_bits[f.b] + num_bits[f.c] +
>		num_bits[f.d];
>}
>
>Would this be faster, in reality, than shifts and iteration? 
>

    Massively.  Look at the code produced - it is generally two or three
instructions per byte. 

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Kevin D. Quitt         demott!kdq   kdq at demott.com
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