which bits are set

[Eychaner, Glenn C.]

In article <1990Dec18.093905.17196 at kithrup.COM>, sef at kithrup.COM (Sean Eric Fagan) writes...
>In article <15598:Dec1804:57:0390 at kramden.acf.nyu.edu> brnstnd at kramden.acf.nyu.edu (Dan Bernstein) writes:
>>Eek. Why do you want to make this so slow?
> 
Ok, to throw my two cents in, this is the algorithm I use...

int bit_set_array [SIZE];

void test_for_bits (int test_int)
{
int j = 0;

while (test_int) {
    bit_set_array [j] = test_int & 1;
    test_int >>= 1;
    j++;
    }
for (; j < SIZE; j++) bit_set_array [j] = 0;
}

Note that this has the advantage of dropping out if test_int is small.
Alternatively:

while (j < SIZE) {

has the advantage of not filling the array at the end.
(I hope this is right.  It's a conversion from my parity calculation program,
 which is:)

parity = 0;
while (test_int) {
    parity ^= test_int & 1;
    test_int >>= 1;
    }
return (parity);

I love bitwise operators!

Glenn Eychaner   |Eychaner at SunCub.Caltech.edu |Remember: It is easier to ride a
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