/*
 * Copyright (c) 2013 Richard Braun.
 *
 * This program is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program.  If not, see <http://www.gnu.org/licenses/>.
 *
 *
 * Arbitrary-length bit arrays.
 */

#ifndef _KERN_BITMAP_H
#define _KERN_BITMAP_H

#include <kern/limits.h>
#include <kern/macros.h>
#include <kern/string.h>
#include <machine/atomic.h>

#define BITMAP_LONGS(nr_bits) DIV_CEIL(nr_bits, LONG_BIT)

/*
 * Declare a bitmap.
 */
#define BITMAP_DECLARE(name, nr_bits) unsigned long name[BITMAP_LONGS(nr_bits)]

/*
 * Helper functions.
 */

static inline void
bitmap_lookup(volatile unsigned long **bm, int *bit)
{
    int i;

    i = BITMAP_LONGS(*bit + 1) - 1;
    *bm += i;
    *bit -= i * LONG_BIT;
}

static inline unsigned long
bitmap_mask(int bit)
{
    return (1UL << bit);
}

/*
 * Public interface.
 */

/*
 * Initialize a bitmap, setting all bits to 0.
 */
static inline void
bitmap_init(unsigned long *bm, int nr_bits)
{
    int n;

    n = BITMAP_LONGS(nr_bits);
    memset(bm, 0, n * sizeof(unsigned long));
}

static inline void
bitmap_set(volatile unsigned long *bm, int bit)
{
    if (bit >= LONG_BIT)
        bitmap_lookup(&bm, &bit);

    *bm |= bitmap_mask(bit);
}

static inline void
bitmap_set_atomic(volatile unsigned long *bm, int bit)
{
    if (bit >= LONG_BIT)
        bitmap_lookup(&bm, &bit);

    atomic_or(bm, bitmap_mask(bit));
}

static inline void
bitmap_clear(volatile unsigned long *bm, int bit)
{
    if (bit >= LONG_BIT)
        bitmap_lookup(&bm, &bit);

    *bm &= ~bitmap_mask(bit);
}

static inline void
bitmap_clear_atomic(volatile unsigned long *bm, int bit)
{
    if (bit >= LONG_BIT)
        bitmap_lookup(&bm, &bit);

    atomic_and(bm, ~bitmap_mask(bit));
}

static inline int
bitmap_test(volatile unsigned long *bm, int bit)
{
    if (bit >= LONG_BIT)
        bitmap_lookup(&bm, &bit);

    return ((*bm & bitmap_mask(bit)) != 0);
}

/*
 * Return the index of the next set bit in the bitmap, starting (and
 * including) the given bit index, or -1 if the bitmap is empty.
 */
static inline int
bitmap_find_next(volatile unsigned long *bm, int nr_bits, int bit)
{
    volatile unsigned long *start, *end;
    unsigned long word;

    start = bm;
    end = bm + BITMAP_LONGS(nr_bits);

    if (bit >= LONG_BIT)
        bitmap_lookup(&bm, &bit);

    word = *bm;

    if (bit < LONG_BIT)
        word &= ~(bitmap_mask(bit) - 1);

    for (;;) {
        bit = __builtin_ffsl(word);

        if (bit != 0)
            return ((bm - start) * LONG_BIT) + bit - 1;

        bm++;

        if (bm >= end)
            return -1;

        word = *bm;
    }
}

static inline int
bitmap_find_first(volatile unsigned long *bm, int nr_bits)
{
    return bitmap_find_next(bm, nr_bits, 0);
}

#endif /* _KERN_BITMAP_H */