unsigned int reverse(unsigned int num, int bits)
{
int ii;
unsigned int n = num&1;
for(ii = 1; ii < bits; ii++)
{
num >>= 1;
n <<= 1;
n |= num&1;
}
return n;
}

用個表效率是最高的了。如用個256格的表，則每八個比特，只要一次運算。理論上效率提高了八倍。