DragonStub/inc/dragonstub/linux/div64.h

/* SPDX-License-Identifier: GPL-2.0 */
#ifndef _ASM_GENERIC_DIV64_H
#define _ASM_GENERIC_DIV64_H
/*
 * Copyright (C) 2003 Bernardo Innocenti <[email protected]>
 * 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 "../types.h"
#include "compiler.h"
#include "bitsperlong.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.
//  *
//  * (It is unfortunate that gcc doesn't perform all this internally.)
//  */

// #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 (__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 */