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1/* SPDX-License-Identifier: GPL-2.0 */2#ifndef _ASM_GENERIC_DIV64_H3#define _ASM_GENERIC_DIV64_H4/*5 * Copyright (C) 2003 Bernardo Innocenti <bernie@develer.com>6 * Based on former asm-ppc/div64.h and asm-m68knommu/div64.h7 *8 * Optimization for constant divisors on 32-bit machines:9 * Copyright (C) 2006-2015 Nicolas Pitre10 *11 * The semantics of do_div() is, in C++ notation, observing that the name12 * is a function-like macro and the n parameter has the semantics of a C++13 * reference:14 *15 * uint32_t do_div(uint64_t &n, uint32_t base)16 * {17 * uint32_t remainder = n % base;18 * n = n / base;19 * return remainder;20 * }21 *22 * NOTE: macro parameter n is evaluated multiple times,23 * beware of side effects!24 */25 26#include <linux/types.h>27#include <linux/compiler.h>28 29#if BITS_PER_LONG == 6430 31/**32 * do_div - returns 2 values: calculate remainder and update new dividend33 * @n: uint64_t dividend (will be updated)34 * @base: uint32_t divisor35 *36 * Summary:37 * ``uint32_t remainder = n % base;``38 * ``n = n / base;``39 *40 * Return: (uint32_t)remainder41 *42 * NOTE: macro parameter @n is evaluated multiple times,43 * beware of side effects!44 */45# define do_div(n,base) ({ \46 uint32_t __base = (base); \47 uint32_t __rem; \48 __rem = ((uint64_t)(n)) % __base; \49 (n) = ((uint64_t)(n)) / __base; \50 __rem; \51 })52 53#elif BITS_PER_LONG == 3254 55#include <linux/log2.h>56 57/*58 * If the divisor happens to be constant, we determine the appropriate59 * inverse at compile time to turn the division into a few inline60 * multiplications which ought to be much faster.61 *62 * (It is unfortunate that gcc doesn't perform all this internally.)63 */64 65#define __div64_const32(n, ___b) \66({ \67 /* \68 * Multiplication by reciprocal of b: n / b = n * (p / b) / p \69 * \70 * We rely on the fact that most of this code gets optimized \71 * away at compile time due to constant propagation and only \72 * a few multiplication instructions should remain. \73 * Hence this monstrous macro (static inline doesn't always \74 * do the trick here). \75 */ \76 uint64_t ___res, ___x, ___t, ___m, ___n = (n); \77 uint32_t ___p, ___bias; \78 \79 /* determine MSB of b */ \80 ___p = 1 << ilog2(___b); \81 \82 /* compute m = ((p << 64) + b - 1) / b */ \83 ___m = (~0ULL / ___b) * ___p; \84 ___m += (((~0ULL % ___b + 1) * ___p) + ___b - 1) / ___b; \85 \86 /* one less than the dividend with highest result */ \87 ___x = ~0ULL / ___b * ___b - 1; \88 \89 /* test our ___m with res = m * x / (p << 64) */ \90 ___res = ((___m & 0xffffffff) * (___x & 0xffffffff)) >> 32; \91 ___t = ___res += (___m & 0xffffffff) * (___x >> 32); \92 ___res += (___x & 0xffffffff) * (___m >> 32); \93 ___t = (___res < ___t) ? (1ULL << 32) : 0; \94 ___res = (___res >> 32) + ___t; \95 ___res += (___m >> 32) * (___x >> 32); \96 ___res /= ___p; \97 \98 /* Now sanitize and optimize what we've got. */ \99 if (~0ULL % (___b / (___b & -___b)) == 0) { \100 /* special case, can be simplified to ... */ \101 ___n /= (___b & -___b); \102 ___m = ~0ULL / (___b / (___b & -___b)); \103 ___p = 1; \104 ___bias = 1; \105 } else if (___res != ___x / ___b) { \106 /* \107 * We can't get away without a bias to compensate \108 * for bit truncation errors. To avoid it we'd need an \109 * additional bit to represent m which would overflow \110 * a 64-bit variable. \111 * \112 * Instead we do m = p / b and n / b = (n * m + m) / p. \113 */ \114 ___bias = 1; \115 /* Compute m = (p << 64) / b */ \116 ___m = (~0ULL / ___b) * ___p; \117 ___m += ((~0ULL % ___b + 1) * ___p) / ___b; \118 } else { \119 /* \120 * Reduce m / p, and try to clear bit 31 of m when \121 * possible, otherwise that'll need extra overflow \122 * handling later. \123 */ \124 uint32_t ___bits = -(___m & -___m); \125 ___bits |= ___m >> 32; \126 ___bits = (~___bits) << 1; \127 /* \128 * If ___bits == 0 then setting bit 31 is unavoidable. \129 * Simply apply the maximum possible reduction in that \130 * case. Otherwise the MSB of ___bits indicates the \131 * best reduction we should apply. \132 */ \133 if (!___bits) { \134 ___p /= (___m & -___m); \135 ___m /= (___m & -___m); \136 } else { \137 ___p >>= ilog2(___bits); \138 ___m >>= ilog2(___bits); \139 } \140 /* No bias needed. */ \141 ___bias = 0; \142 } \143 \144 /* \145 * Now we have a combination of 2 conditions: \146 * \147 * 1) whether or not we need to apply a bias, and \148 * \149 * 2) whether or not there might be an overflow in the cross \150 * product determined by (___m & ((1 << 63) | (1 << 31))). \151 * \152 * Select the best way to do (m_bias + m * n) / (1 << 64). \153 * From now on there will be actual runtime code generated. \154 */ \155 ___res = __arch_xprod_64(___m, ___n, ___bias); \156 \157 ___res /= ___p; \158})159 160#ifndef __arch_xprod_64161/*162 * Default C implementation for __arch_xprod_64()163 *164 * Prototype: uint64_t __arch_xprod_64(const uint64_t m, uint64_t n, bool bias)165 * Semantic: retval = ((bias ? m : 0) + m * n) >> 64166 *167 * The product is a 128-bit value, scaled down to 64 bits.168 * Assuming constant propagation to optimize away unused conditional code.169 * Architectures may provide their own optimized assembly implementation.170 */171static inline uint64_t __arch_xprod_64(const uint64_t m, uint64_t n, bool bias)172{173 uint32_t m_lo = m;174 uint32_t m_hi = m >> 32;175 uint32_t n_lo = n;176 uint32_t n_hi = n >> 32;177 uint64_t res;178 uint32_t res_lo, res_hi, tmp;179 180 if (!bias) {181 res = ((uint64_t)m_lo * n_lo) >> 32;182 } else if (!(m & ((1ULL << 63) | (1ULL << 31)))) {183 /* there can't be any overflow here */184 res = (m + (uint64_t)m_lo * n_lo) >> 32;185 } else {186 res = m + (uint64_t)m_lo * n_lo;187 res_lo = res >> 32;188 res_hi = (res_lo < m_hi);189 res = res_lo | ((uint64_t)res_hi << 32);190 }191 192 if (!(m & ((1ULL << 63) | (1ULL << 31)))) {193 /* there can't be any overflow here */194 res += (uint64_t)m_lo * n_hi;195 res += (uint64_t)m_hi * n_lo;196 res >>= 32;197 } else {198 res += (uint64_t)m_lo * n_hi;199 tmp = res >> 32;200 res += (uint64_t)m_hi * n_lo;201 res_lo = res >> 32;202 res_hi = (res_lo < tmp);203 res = res_lo | ((uint64_t)res_hi << 32);204 }205 206 res += (uint64_t)m_hi * n_hi;207 208 return res;209}210#endif211 212#ifndef __div64_32213extern uint32_t __div64_32(uint64_t *dividend, uint32_t divisor);214#endif215 216/* The unnecessary pointer compare is there217 * to check for type safety (n must be 64bit)218 */219# define do_div(n,base) ({ \220 uint32_t __base = (base); \221 uint32_t __rem; \222 (void)(((typeof((n)) *)0) == ((uint64_t *)0)); \223 if (__builtin_constant_p(__base) && \224 is_power_of_2(__base)) { \225 __rem = (n) & (__base - 1); \226 (n) >>= ilog2(__base); \227 } else if (__builtin_constant_p(__base) && \228 __base != 0) { \229 uint32_t __res_lo, __n_lo = (n); \230 (n) = __div64_const32(n, __base); \231 /* the remainder can be computed with 32-bit regs */ \232 __res_lo = (n); \233 __rem = __n_lo - __res_lo * __base; \234 } else if (likely(((n) >> 32) == 0)) { \235 __rem = (uint32_t)(n) % __base; \236 (n) = (uint32_t)(n) / __base; \237 } else { \238 __rem = __div64_32(&(n), __base); \239 } \240 __rem; \241 })242 243#else /* BITS_PER_LONG == ?? */244 245# error do_div() does not yet support the C64246 247#endif /* BITS_PER_LONG */248 249#endif /* _ASM_GENERIC_DIV64_H */250