/* SPDX-License-Identifier: GPL-2.0 */
#ifndef _ASM_GENERIC_DIV64_H
#define _ASM_GENERIC_DIV64_H
/*
 * Copyright (C) 2003 Bernardo Innocenti <bernie@develer.com>
 * Based on former asm-ppc/div64.h and asm-m68knommu/div64.h
 *
 * Optimization for constant divisors on 32-bit machines:
 * Copyright (C) 2006-2015 Nicolas Pitre
 *
 * The semantics of do_div() is, in C++ notation, observing that the name
 * is a function-like macro and the n parameter has the semantics of a C++
 * reference:
 *
 * uint32_t do_div(uint64_t &n, uint32_t base)
 * {
 *      uint32_t remainder = n % base;
 *      n = n / base;
 *      return remainder;
 * }
 *
 * NOTE: macro parameter n is evaluated multiple times,
 *       beware of side effects!
 */

#include <linux/types.h>
#include <linux/compiler.h>

#if BITS_PER_LONG == 64

/**
 * do_div - returns 2 values: calculate remainder and update new dividend
 * @n: uint64_t dividend (will be updated)
 * @base: uint32_t divisor
 *
 * Summary:
 * ``uint32_t remainder = n % base;``
 * ``n = n / base;``
 *
 * Return: (uint32_t)remainder
 *
 * NOTE: macro parameter @n is evaluated multiple times,
 * beware of side effects!
 */
# define do_div(n,base) ({                                      \
        uint32_t __base = (base);                               \
        uint32_t __rem;                                         \
        __rem = ((uint64_t)(n)) % __base;                       \
        (n) = ((uint64_t)(n)) / __base;                         \
        __rem;                                                  \
 })

#elif BITS_PER_LONG == 32

#include <linux/log2.h>

/*
 * If the divisor happens to be constant, we determine the appropriate
 * inverse at compile time to turn the division into a few inline
 * multiplications which ought to be much faster. And yet only if compiling
 * with a sufficiently recent gcc version to perform proper 64-bit constant
 * propagation.
 *
 * (It is unfortunate that gcc doesn't perform all this internally.)
 */

#ifndef __div64_const32_is_OK
#define __div64_const32_is_OK (__GNUC__ >= 4)
#endif

#define __div64_const32(n, ___b)                                        \
({                                                                      \
        /*                                                              \
         * Multiplication by reciprocal of b: n / b = n * (p / b) / p   \
         *                                                              \
         * We rely on the fact that most of this code gets optimized    \
         * away at compile time due to constant propagation and only    \
         * a few multiplication instructions should remain.             \
         * Hence this monstrous macro (static inline doesn't always     \
         * do the trick here).                                          \
         */                                                             \
        uint64_t ___res, ___x, ___t, ___m, ___n = (n);                  \
        uint32_t ___p, ___bias;                                         \
                                                                        \
        /* determine MSB of b */                                        \
        ___p = 1 << ilog2(___b);                                        \
                                                                        \
        /* compute m = ((p << 64) + b - 1) / b */                       \
        ___m = (~0ULL / ___b) * ___p;                                   \
        ___m += (((~0ULL % ___b + 1) * ___p) + ___b - 1) / ___b;        \
                                                                        \
        /* one less than the dividend with highest result */            \
        ___x = ~0ULL / ___b * ___b - 1;                                 \
                                                                        \
        /* test our ___m with res = m * x / (p << 64) */                \
        ___res = ((___m & 0xffffffff) * (___x & 0xffffffff)) >> 32;     \
        ___t = ___res += (___m & 0xffffffff) * (___x >> 32);            \
        ___res += (___x & 0xffffffff) * (___m >> 32);                   \
        ___t = (___res < ___t) ? (1ULL << 32) : 0;                      \
        ___res = (___res >> 32) + ___t;                                 \
        ___res += (___m >> 32) * (___x >> 32);                          \
        ___res /= ___p;                                                 \
                                                                        \
        /* Now sanitize and optimize what we've got. */                 \
        if (~0ULL % (___b / (___b & -___b)) == 0) {                     \
                /* special case, can be simplified to ... */            \
                ___n /= (___b & -___b);                                 \
                ___m = ~0ULL / (___b / (___b & -___b));                 \
                ___p = 1;                                               \
                ___bias = 1;                                            \
        } else if (___res != ___x / ___b) {                             \
                /*                                                      \
                 * We can't get away without a bias to compensate       \
                 * for bit truncation errors.  To avoid it we'd need an \
                 * additional bit to represent m which would overflow   \
                 * a 64-bit variable.                                   \
                 *                                                      \
                 * Instead we do m = p / b and n / b = (n * m + m) / p. \
                 */                                                     \
                ___bias = 1;                                            \
                /* Compute m = (p << 64) / b */                         \
                ___m = (~0ULL / ___b) * ___p;                           \
                ___m += ((~0ULL % ___b + 1) * ___p) / ___b;             \
        } else {                                                        \
                /*                                                      \
                 * Reduce m / p, and try to clear bit 31 of m when      \
                 * possible, otherwise that'll need extra overflow      \
                 * handling later.                                      \
                 */                                                     \
                uint32_t ___bits = -(___m & -___m);                     \
                ___bits |= ___m >> 32;                                  \
                ___bits = (~___bits) << 1;                              \
                /*                                                      \
                 * If ___bits == 0 then setting bit 31 is  unavoidable. \
                 * Simply apply the maximum possible reduction in that  \
                 * case. Otherwise the MSB of ___bits indicates the     \
                 * best reduction we should apply.                      \
                 */                                                     \
                if (!___bits) {                                         \
                        ___p /= (___m & -___m);                         \
                        ___m /= (___m & -___m);                         \
                } else {                                                \
                        ___p >>= ilog2(___bits);                        \
                        ___m >>= ilog2(___bits);                        \
                }                                                       \
                /* No bias needed. */                                   \
                ___bias = 0;                                            \
        }                                                               \
                                                                        \
        /*                                                              \
         * Now we have a combination of 2 conditions:                   \
         *                                                              \
         * 1) whether or not we need to apply a bias, and               \
         *                                                              \
         * 2) whether or not there might be an overflow in the cross    \
         *    product determined by (___m & ((1 << 63) | (1 << 31))).   \
         *                                                              \
         * Select the best way to do (m_bias + m * n) / (1 << 64).      \
         * From now on there will be actual runtime code generated.     \
         */                                                             \
        ___res = __arch_xprod_64(___m, ___n, ___bias);                  \
                                                                        \
        ___res /= ___p;                                                 \
})

#ifndef __arch_xprod_64
/*
 * Default C implementation for __arch_xprod_64()
 *
 * Prototype: uint64_t __arch_xprod_64(const uint64_t m, uint64_t n, bool bias)
 * Semantic:  retval = ((bias ? m : 0) + m * n) >> 64
 *
 * The product is a 128-bit value, scaled down to 64 bits.
 * Assuming constant propagation to optimize away unused conditional code.
 * Architectures may provide their own optimized assembly implementation.
 */
static inline uint64_t __arch_xprod_64(const uint64_t m, uint64_t n, bool bias)
{
        uint32_t m_lo = m;
        uint32_t m_hi = m >> 32;
        uint32_t n_lo = n;
        uint32_t n_hi = n >> 32;
        uint64_t res;
        uint32_t res_lo, res_hi, tmp;

        if (!bias) {
                res = ((uint64_t)m_lo * n_lo) >> 32;
        } else if (!(m & ((1ULL << 63) | (1ULL << 31)))) {
                /* there can't be any overflow here */
                res = (m + (uint64_t)m_lo * n_lo) >> 32;
        } else {
                res = m + (uint64_t)m_lo * n_lo;
                res_lo = res >> 32;
                res_hi = (res_lo < m_hi);
                res = res_lo | ((uint64_t)res_hi << 32);
        }

        if (!(m & ((1ULL << 63) | (1ULL << 31)))) {
                /* there can't be any overflow here */
                res += (uint64_t)m_lo * n_hi;
                res += (uint64_t)m_hi * n_lo;
                res >>= 32;
        } else {
                res += (uint64_t)m_lo * n_hi;
                tmp = res >> 32;
                res += (uint64_t)m_hi * n_lo;
                res_lo = res >> 32;
                res_hi = (res_lo < tmp);
                res = res_lo | ((uint64_t)res_hi << 32);
        }

        res += (uint64_t)m_hi * n_hi;

        return res;
}
#endif

#ifndef __div64_32
extern uint32_t __div64_32(uint64_t *dividend, uint32_t divisor);
#endif

/* The unnecessary pointer compare is there
 * to check for type safety (n must be 64bit)
 */
# define do_div(n,base) ({                              \
        uint32_t __base = (base);                       \
        uint32_t __rem;                                 \
        (void)(((typeof((n)) *)0) == ((uint64_t *)0));  \
        if (__builtin_constant_p(__base) &&             \
            is_power_of_2(__base)) {                    \
                __rem = (n) & (__base - 1);             \
                (n) >>= ilog2(__base);                  \
        } else if (__div64_const32_is_OK &&             \
                   __builtin_constant_p(__base) &&      \
                   __base != 0) {                       \
                uint32_t __res_lo, __n_lo = (n);        \
                (n) = __div64_const32(n, __base);       \
                /* the remainder can be computed with 32-bit regs */ \
                __res_lo = (n);                         \
                __rem = __n_lo - __res_lo * __base;     \
        } else if (likely(((n) >> 32) == 0)) {          \
                __rem = (uint32_t)(n) % __base;         \
                (n) = (uint32_t)(n) / __base;           \
        } else                                          \
                __rem = __div64_32(&(n), __base);       \
        __rem;                                          \
 })

#else /* BITS_PER_LONG == ?? */

# error do_div() does not yet support the C64

#endif /* BITS_PER_LONG */

#endif /* _ASM_GENERIC_DIV64_H */