// SPDX-License-Identifier: GPL-2.0
/*
 * Copyright (C) 2003 Bernardo Innocenti <bernie@develer.com>
 *
 * Based on former do_div() implementation from asm-parisc/div64.h:
 *      Copyright (C) 1999 Hewlett-Packard Co
 *      Copyright (C) 1999 David Mosberger-Tang <davidm@hpl.hp.com>
 *
 *
 * Generic C version of 64bit/32bit division and modulo, with
 * 64bit result and 32bit remainder.
 *
 * The fast case for (n>>32 == 0) is handled inline by do_div().
 *
 * Code generated for this function might be very inefficient
 * for some CPUs. __div64_32() can be overridden by linking arch-specific
 * assembly versions such as arch/ppc/lib/div64.S and arch/sh/lib/div64.S
 * or by defining a preprocessor macro in arch/include/asm/div64.h.
 */

#include <linux/export.h>
#include <linux/kernel.h>
#include <linux/math64.h>

/* Not needed on 64bit architectures */
#if BITS_PER_LONG == 32

#ifndef __div64_32
uint32_t __attribute__((weak)) __div64_32(uint64_t *n, uint32_t base)
{
        uint64_t rem = *n;
        uint64_t b = base;
        uint64_t res, d = 1;
        uint32_t high = rem >> 32;

        /* Reduce the thing a bit first */
        res = 0;
        if (high >= base) {
                high /= base;
                res = (uint64_t) high << 32;
                rem -= (uint64_t) (high*base) << 32;
        }

        while ((int64_t)b > 0 && b < rem) {
                b = b+b;
                d = d+d;
        }

        do {
                if (rem >= b) {
                        rem -= b;
                        res += d;
                }
                b >>= 1;
                d >>= 1;
        } while (d);

        *n = res;
        return rem;
}
EXPORT_SYMBOL(__div64_32);
#endif

/**
 * div_s64_rem - signed 64bit divide with 64bit divisor and remainder
 * @dividend:   64bit dividend
 * @divisor:    64bit divisor
 * @remainder:  64bit remainder
 */
#ifndef div_s64_rem
s64 div_s64_rem(s64 dividend, s32 divisor, s32 *remainder)
{
        u64 quotient;

        if (dividend < 0) {
                quotient = div_u64_rem(-dividend, abs(divisor), (u32 *)remainder);
                *remainder = -*remainder;
                if (divisor > 0)
                        quotient = -quotient;
        } else {
                quotient = div_u64_rem(dividend, abs(divisor), (u32 *)remainder);
                if (divisor < 0)
                        quotient = -quotient;
        }
        return quotient;
}
EXPORT_SYMBOL(div_s64_rem);
#endif

/**
 * div64_u64_rem - unsigned 64bit divide with 64bit divisor and remainder
 * @dividend:   64bit dividend
 * @divisor:    64bit divisor
 * @remainder:  64bit remainder
 *
 * This implementation is a comparable to algorithm used by div64_u64.
 * But this operation, which includes math for calculating the remainder,
 * is kept distinct to avoid slowing down the div64_u64 operation on 32bit
 * systems.
 */
#ifndef div64_u64_rem
u64 div64_u64_rem(u64 dividend, u64 divisor, u64 *remainder)
{
        u32 high = divisor >> 32;
        u64 quot;

        if (high == 0) {
                u32 rem32;
                quot = div_u64_rem(dividend, divisor, &rem32);
                *remainder = rem32;
        } else {
                int n = 1 + fls(high);
                quot = div_u64(dividend >> n, divisor >> n);

                if (quot != 0)
                        quot--;

                *remainder = dividend - quot * divisor;
                if (*remainder >= divisor) {
                        quot++;
                        *remainder -= divisor;
                }
        }

        return quot;
}
EXPORT_SYMBOL(div64_u64_rem);
#endif

/**
 * div64_u64 - unsigned 64bit divide with 64bit divisor
 * @dividend:   64bit dividend
 * @divisor:    64bit divisor
 *
 * This implementation is a modified version of the algorithm proposed
 * by the book 'Hacker's Delight'.  The original source and full proof
 * can be found here and is available for use without restriction.
 *
 * 'http://www.hackersdelight.org/hdcodetxt/divDouble.c.txt'
 */
#ifndef div64_u64
u64 div64_u64(u64 dividend, u64 divisor)
{
        u32 high = divisor >> 32;
        u64 quot;

        if (high == 0) {
                quot = div_u64(dividend, divisor);
        } else {
                int n = 1 + fls(high);
                quot = div_u64(dividend >> n, divisor >> n);

                if (quot != 0)
                        quot--;
                if ((dividend - quot * divisor) >= divisor)
                        quot++;
        }

        return quot;
}
EXPORT_SYMBOL(div64_u64);
#endif

/**
 * div64_s64 - signed 64bit divide with 64bit divisor
 * @dividend:   64bit dividend
 * @divisor:    64bit divisor
 */
#ifndef div64_s64
s64 div64_s64(s64 dividend, s64 divisor)
{
        s64 quot, t;

        quot = div64_u64(abs(dividend), abs(divisor));
        t = (dividend ^ divisor) >> 63;

        return (quot ^ t) - t;
}
EXPORT_SYMBOL(div64_s64);
#endif

#endif /* BITS_PER_LONG == 32 */

/*
 * Iterative div/mod for use when dividend is not expected to be much
 * bigger than divisor.
 */
u32 iter_div_u64_rem(u64 dividend, u32 divisor, u64 *remainder)
{
        return __iter_div_u64_rem(dividend, divisor, remainder);
}
EXPORT_SYMBOL(iter_div_u64_rem);

#ifndef mul_u64_u64_div_u64
u64 mul_u64_u64_div_u64(u64 a, u64 b, u64 c)
{
        u64 res = 0, div, rem;
        int shift;

        /* can a * b overflow ? */
        if (ilog2(a) + ilog2(b) > 62) {
                /*
                 * (b * a) / c is equal to
                 *
                 *      (b / c) * a +
                 *      (b % c) * a / c
                 *
                 * if nothing overflows. Can the 1st multiplication
                 * overflow? Yes, but we do not care: this can only
                 * happen if the end result can't fit in u64 anyway.
                 *
                 * So the code below does
                 *
                 *      res = (b / c) * a;
                 *      b = b % c;
                 */
                div = div64_u64_rem(b, c, &rem);
                res = div * a;
                b = rem;

                shift = ilog2(a) + ilog2(b) - 62;
                if (shift > 0) {
                        /* drop precision */
                        b >>= shift;
                        c >>= shift;
                        if (!c)
                                return res;
                }
        }

        return res + div64_u64(a * b, c);
}
#endif