root/lib/hweight.c

DEFINITIONS

1. hweight32
2. hweight16
3. hweight8
4. hweight64

#include <linux/module.h>
#include <linux/bitops.h>
#include <asm/types.h>

/**
 * hweightN - returns the hamming weight of a N-bit word
 * @x: the word to weigh
 *
 * The Hamming Weight of a number is the total number of bits set in it.
 */

unsigned int hweight32(unsigned int w)
{
        unsigned int res = w - ((w >> 1) & 0x55555555);
        res = (res & 0x33333333) + ((res >> 2) & 0x33333333);
        res = (res + (res >> 4)) & 0x0F0F0F0F;
        res = res + (res >> 8);
        return (res + (res >> 16)) & 0x000000FF;
}
EXPORT_SYMBOL(hweight32);

unsigned int hweight16(unsigned int w)
{
        unsigned int res = w - ((w >> 1) & 0x5555);
        res = (res & 0x3333) + ((res >> 2) & 0x3333);
        res = (res + (res >> 4)) & 0x0F0F;
        return (res + (res >> 8)) & 0x00FF;
}
EXPORT_SYMBOL(hweight16);

unsigned int hweight8(unsigned int w)
{
        unsigned int res = w - ((w >> 1) & 0x55);
        res = (res & 0x33) + ((res >> 2) & 0x33);
        return (res + (res >> 4)) & 0x0F;
}
EXPORT_SYMBOL(hweight8);

unsigned long hweight64(__u64 w)
{
#if BITS_PER_LONG == 32
        return hweight32((unsigned int)(w >> 32)) + hweight32((unsigned int)w);
#elif BITS_PER_LONG == 64
#ifdef ARCH_HAS_FAST_MULTIPLIER
        w -= (w >> 1) & 0x5555555555555555ul;
        w =  (w & 0x3333333333333333ul) + ((w >> 2) & 0x3333333333333333ul);
        w =  (w + (w >> 4)) & 0x0f0f0f0f0f0f0f0ful;
        return (w * 0x0101010101010101ul) >> 56;
#else
        __u64 res = w - ((w >> 1) & 0x5555555555555555ul);
        res = (res & 0x3333333333333333ul) + ((res >> 2) & 0x3333333333333333ul);
        res = (res + (res >> 4)) & 0x0F0F0F0F0F0F0F0Ful;
        res = res + (res >> 8);
        res = res + (res >> 16);
        return (res + (res >> 32)) & 0x00000000000000FFul;
#endif
#endif
}
EXPORT_SYMBOL(hweight64);