// SPDX-License-Identifier: GPL-2.0
#include <linux/bitops.h>
#include <linux/bug.h>
#include <linux/export.h>
#include <linux/limits.h>
#include <linux/math.h>
#include <linux/minmax.h>
#include <linux/types.h>

#include <linux/reciprocal_div.h>

/*
 * For a description of the algorithm please have a look at
 * include/linux/reciprocal_div.h
 */

struct reciprocal_value reciprocal_value(u32 d)
{
        struct reciprocal_value R;
        u64 m;
        int l;

        l = fls(d - 1);
        m = ((1ULL << 32) * ((1ULL << l) - d));
        do_div(m, d);
        ++m;
        R.m = (u32)m;
        R.sh1 = min(l, 1);
        R.sh2 = max(l - 1, 0);

        return R;
}
EXPORT_SYMBOL(reciprocal_value);

struct reciprocal_value_adv reciprocal_value_adv(u32 d, u8 prec)
{
        struct reciprocal_value_adv R;
        u32 l, post_shift;
        u64 mhigh, mlow;

        /* ceil(log2(d)) */
        l = fls(d - 1);
        /* NOTE: mlow/mhigh could overflow u64 when l == 32. This case needs to
         * be handled before calling "reciprocal_value_adv", please see the
         * comment at include/linux/reciprocal_div.h.
         */
        WARN(l == 32,
             "ceil(log2(0x%08x)) == 32, %s doesn't support such divisor",
             d, __func__);
        post_shift = l;
        mlow = 1ULL << (32 + l);
        do_div(mlow, d);
        mhigh = (1ULL << (32 + l)) + (1ULL << (32 + l - prec));
        do_div(mhigh, d);

        for (; post_shift > 0; post_shift--) {
                u64 lo = mlow >> 1, hi = mhigh >> 1;

                if (lo >= hi)
                        break;

                mlow = lo;
                mhigh = hi;
        }

        R.m = (u32)mhigh;
        R.sh = post_shift;
        R.exp = l;
        R.is_wide_m = mhigh > U32_MAX;

        return R;
}
EXPORT_SYMBOL(reciprocal_value_adv);