// SPDX-License-Identifier: GPL-2.0-or-later
/* bit search implementation
 *
 * Copyright (C) 2004 Red Hat, Inc. All Rights Reserved.
 * Written by David Howells (dhowells@redhat.com)
 *
 * Copyright (C) 2008 IBM Corporation
 * 'find_last_bit' is written by Rusty Russell <rusty@rustcorp.com.au>
 * (Inspired by David Howell's find_next_bit implementation)
 *
 * Rewritten by Yury Norov <yury.norov@gmail.com> to decrease
 * size and improve performance, 2015.
 */

#include <linux/bitops.h>
#include <linux/bitmap.h>
#include <linux/export.h>
#include <linux/math.h>
#include <linux/minmax.h>
#include <linux/swab.h>
#include <linux/random.h>

/*
 * Common helper for find_bit() function family
 * @FETCH: The expression that fetches and pre-processes each word of bitmap(s)
 * @MUNGE: The expression that post-processes a word containing found bit (may be empty)
 * @size: The bitmap size in bits
 */
#define FIND_FIRST_BIT(FETCH, MUNGE, size)                                      \
({                                                                              \
        unsigned long idx, val, sz = (size);                                    \
                                                                                \
        for (idx = 0; idx * BITS_PER_LONG < sz; idx++) {                        \
                val = (FETCH);                                                  \
                if (val) {                                                      \
                        sz = min(idx * BITS_PER_LONG + __ffs(MUNGE(val)), sz);  \
                        break;                                                  \
                }                                                               \
        }                                                                       \
                                                                                \
        sz;                                                                     \
})

/*
 * Common helper for find_next_bit() function family
 * @FETCH: The expression that fetches and pre-processes each word of bitmap(s)
 * @MUNGE: The expression that post-processes a word containing found bit (may be empty)
 * @size: The bitmap size in bits
 * @start: The bitnumber to start searching at
 */
#define FIND_NEXT_BIT(FETCH, MUNGE, size, start)                                \
({                                                                              \
        unsigned long mask, idx, tmp, sz = (size), __start = (start);           \
                                                                                \
        if (unlikely(__start >= sz))                                            \
                goto out;                                                       \
                                                                                \
        mask = MUNGE(BITMAP_FIRST_WORD_MASK(__start));                          \
        idx = __start / BITS_PER_LONG;                                          \
                                                                                \
        for (tmp = (FETCH) & mask; !tmp; tmp = (FETCH)) {                       \
                if ((idx + 1) * BITS_PER_LONG >= sz)                            \
                        goto out;                                               \
                idx++;                                                          \
        }                                                                       \
                                                                                \
        sz = min(idx * BITS_PER_LONG + __ffs(MUNGE(tmp)), sz);                  \
out:                                                                            \
        sz;                                                                     \
})

#define FIND_NTH_BIT(FETCH, size, num)                                          \
({                                                                              \
        unsigned long sz = (size), nr = (num), idx, w, tmp = 0;                 \
                                                                                \
        for (idx = 0; (idx + 1) * BITS_PER_LONG <= sz; idx++) {                 \
                if (idx * BITS_PER_LONG + nr >= sz)                             \
                        goto out;                                               \
                                                                                \
                tmp = (FETCH);                                                  \
                w = hweight_long(tmp);                                          \
                if (w > nr)                                                     \
                        goto found;                                             \
                                                                                \
                nr -= w;                                                        \
        }                                                                       \
                                                                                \
        if (sz % BITS_PER_LONG)                                                 \
                tmp = (FETCH) & BITMAP_LAST_WORD_MASK(sz);                      \
found:                                                                          \
        sz = idx * BITS_PER_LONG + fns(tmp, nr);                                \
out:                                                                            \
        sz;                                                                     \
})

#ifndef find_first_bit
/*
 * Find the first set bit in a memory region.
 */
unsigned long _find_first_bit(const unsigned long *addr, unsigned long size)
{
        return FIND_FIRST_BIT(addr[idx], /* nop */, size);
}
EXPORT_SYMBOL(_find_first_bit);
#endif

#ifndef find_first_and_bit
/*
 * Find the first set bit in two memory regions.
 */
unsigned long _find_first_and_bit(const unsigned long *addr1,
                                  const unsigned long *addr2,
                                  unsigned long size)
{
        return FIND_FIRST_BIT(addr1[idx] & addr2[idx], /* nop */, size);
}
EXPORT_SYMBOL(_find_first_and_bit);
#endif

/*
 * Find the first bit set in 1st memory region and unset in 2nd.
 */
unsigned long _find_first_andnot_bit(const unsigned long *addr1,
                                  const unsigned long *addr2,
                                  unsigned long size)
{
        return FIND_FIRST_BIT(addr1[idx] & ~addr2[idx], /* nop */, size);
}
EXPORT_SYMBOL(_find_first_andnot_bit);

/*
 * Find the first set bit in three memory regions.
 */
unsigned long _find_first_and_and_bit(const unsigned long *addr1,
                                      const unsigned long *addr2,
                                      const unsigned long *addr3,
                                      unsigned long size)
{
        return FIND_FIRST_BIT(addr1[idx] & addr2[idx] & addr3[idx], /* nop */, size);
}
EXPORT_SYMBOL(_find_first_and_and_bit);

#ifndef find_first_zero_bit
/*
 * Find the first cleared bit in a memory region.
 */
unsigned long _find_first_zero_bit(const unsigned long *addr, unsigned long size)
{
        return FIND_FIRST_BIT(~addr[idx], /* nop */, size);
}
EXPORT_SYMBOL(_find_first_zero_bit);
#endif

#ifndef find_next_bit
unsigned long _find_next_bit(const unsigned long *addr, unsigned long nbits, unsigned long start)
{
        return FIND_NEXT_BIT(addr[idx], /* nop */, nbits, start);
}
EXPORT_SYMBOL(_find_next_bit);
#endif

unsigned long __find_nth_bit(const unsigned long *addr, unsigned long size, unsigned long n)
{
        return FIND_NTH_BIT(addr[idx], size, n);
}
EXPORT_SYMBOL(__find_nth_bit);

unsigned long __find_nth_and_bit(const unsigned long *addr1, const unsigned long *addr2,
                                 unsigned long size, unsigned long n)
{
        return FIND_NTH_BIT(addr1[idx] & addr2[idx], size, n);
}
EXPORT_SYMBOL(__find_nth_and_bit);

unsigned long __find_nth_andnot_bit(const unsigned long *addr1, const unsigned long *addr2,
                                 unsigned long size, unsigned long n)
{
        return FIND_NTH_BIT(addr1[idx] & ~addr2[idx], size, n);
}
EXPORT_SYMBOL(__find_nth_andnot_bit);

unsigned long __find_nth_and_andnot_bit(const unsigned long *addr1,
                                        const unsigned long *addr2,
                                        const unsigned long *addr3,
                                        unsigned long size, unsigned long n)
{
        return FIND_NTH_BIT(addr1[idx] & addr2[idx] & ~addr3[idx], size, n);
}
EXPORT_SYMBOL(__find_nth_and_andnot_bit);

#ifndef find_next_and_bit
unsigned long _find_next_and_bit(const unsigned long *addr1, const unsigned long *addr2,
                                        unsigned long nbits, unsigned long start)
{
        return FIND_NEXT_BIT(addr1[idx] & addr2[idx], /* nop */, nbits, start);
}
EXPORT_SYMBOL(_find_next_and_bit);
#endif

#ifndef find_next_andnot_bit
unsigned long _find_next_andnot_bit(const unsigned long *addr1, const unsigned long *addr2,
                                        unsigned long nbits, unsigned long start)
{
        return FIND_NEXT_BIT(addr1[idx] & ~addr2[idx], /* nop */, nbits, start);
}
EXPORT_SYMBOL(_find_next_andnot_bit);
#endif

#ifndef find_next_or_bit
unsigned long _find_next_or_bit(const unsigned long *addr1, const unsigned long *addr2,
                                        unsigned long nbits, unsigned long start)
{
        return FIND_NEXT_BIT(addr1[idx] | addr2[idx], /* nop */, nbits, start);
}
EXPORT_SYMBOL(_find_next_or_bit);
#endif

#ifndef find_next_zero_bit
unsigned long _find_next_zero_bit(const unsigned long *addr, unsigned long nbits,
                                         unsigned long start)
{
        return FIND_NEXT_BIT(~addr[idx], /* nop */, nbits, start);
}
EXPORT_SYMBOL(_find_next_zero_bit);
#endif

#ifndef find_last_bit
unsigned long _find_last_bit(const unsigned long *addr, unsigned long size)
{
        if (size) {
                unsigned long val = BITMAP_LAST_WORD_MASK(size);
                unsigned long idx = (size-1) / BITS_PER_LONG;

                do {
                        val &= addr[idx];
                        if (val)
                                return idx * BITS_PER_LONG + __fls(val);

                        val = ~0ul;
                } while (idx--);
        }
        return size;
}
EXPORT_SYMBOL(_find_last_bit);
#endif

unsigned long find_next_clump8(unsigned long *clump, const unsigned long *addr,
                               unsigned long size, unsigned long offset)
{
        offset = find_next_bit(addr, size, offset);
        if (offset == size)
                return size;

        offset = round_down(offset, 8);
        *clump = bitmap_get_value8(addr, offset);

        return offset;
}
EXPORT_SYMBOL(find_next_clump8);

#ifdef __BIG_ENDIAN

#ifndef find_first_zero_bit_le
/*
 * Find the first cleared bit in an LE memory region.
 */
unsigned long _find_first_zero_bit_le(const unsigned long *addr, unsigned long size)
{
        return FIND_FIRST_BIT(~addr[idx], swab, size);
}
EXPORT_SYMBOL(_find_first_zero_bit_le);

#endif

#ifndef find_next_zero_bit_le
unsigned long _find_next_zero_bit_le(const unsigned long *addr,
                                        unsigned long size, unsigned long offset)
{
        return FIND_NEXT_BIT(~addr[idx], swab, size, offset);
}
EXPORT_SYMBOL(_find_next_zero_bit_le);
#endif

#ifndef find_next_bit_le
unsigned long _find_next_bit_le(const unsigned long *addr,
                                unsigned long size, unsigned long offset)
{
        return FIND_NEXT_BIT(addr[idx], swab, size, offset);
}
EXPORT_SYMBOL(_find_next_bit_le);

#endif

#endif /* __BIG_ENDIAN */

/**
 * find_random_bit - find a set bit at random position
 * @addr: The address to base the search on
 * @size: The bitmap size in bits
 *
 * Returns: a position of a random set bit; >= @size otherwise
 */
unsigned long find_random_bit(const unsigned long *addr, unsigned long size)
{
        int w = bitmap_weight(addr, size);

        switch (w) {
        case 0:
                return size;
        case 1:
                /* Performance trick for single-bit bitmaps */
                return find_first_bit(addr, size);
        default:
                return find_nth_bit(addr, size, get_random_u32_below(w));
        }
}
EXPORT_SYMBOL(find_random_bit);