cutils: Add bitmask utilities to bitops

#ifndef __CUTILS_BITOPS_H

#define __CUTILS_BITOPS_H

#include <string.h>

#include <strings.h>

#include <sys/cdefs.h>

__BEGIN_DECLS

/*

 * Bitmask Operations

 *

 * Note this doesn't provide any locking/exclusion, and isn't atomic.

 * Additionally no bounds checking is done on the bitmask array.

 *

 * Example:

 *

 * int num_resources;

 * unsigned int resource_bits[BITS_TO_WORDS(num_resources)];

 * bitmask_init(resource_bits, num_resources);

 * ...

 * int bit = bitmask_ffz(resource_bits, num_resources);

 * bitmask_set(resource_bits, bit);

 * ...

 * if (bitmask_test(resource_bits, bit)) { ... }

 * ...

 * bitmask_clear(resource_bits, bit);

 *

 */

#define BITS_PER_WORD    (sizeof(unsigned int) * 8)

#define BITS_TO_WORDS(x) (((x) + BITS_PER_WORD - 1) / BITS_PER_WORD)

#define BIT_IN_WORD(x)   ((x) % BITS_PER_WORD)

#define BIT_WORD(x)      ((x) / BITS_PER_WORD)

#define BIT_MASK(x)      (1 << BIT_IN_WORD(x))

static inline void bitmask_init(unsigned int *bitmask, int num_bits)

{

    memset(bitmask, 0, BITS_TO_WORDS(num_bits)*sizeof(unsigned int));

}

static inline int bitmask_ffz(unsigned int *bitmask, int num_bits)

{

    int bit, result;

    unsigned int i;

    for (i = 0; i < BITS_TO_WORDS(num_bits); i++) {

        bit = ffs(~bitmask[i]);

        if (bit) {

            // ffs is 1-indexed, return 0-indexed result

            bit--;

            result = BITS_PER_WORD * i + bit;

            if (result >= num_bits)

                return -1;

            return result;

        }

    }

    return -1;

}

static inline void bitmask_set(unsigned int *bitmask, int bit)

{

    bitmask[BIT_WORD(bit)] |= BIT_MASK(bit);

}

static inline void bitmask_clear(unsigned int *bitmask, int bit)

{

    bitmask[BIT_WORD(bit)] &= ~BIT_MASK(bit);

}

static inline bool bitmask_test(unsigned int *bitmask, int bit)

{

    return bitmask[BIT_WORD(bit)] & BIT_MASK(bit);

}

static inline int popcount(unsigned int x)

{

    return __builtin_popcount(x);