1// SPDX-License-Identifier: GPL-2.0 2/* 3 * Copyright (C) 2003 Bernardo Innocenti <bernie@develer.com> 4 * 5 * Based on former do_div() implementation from asm-parisc/div64.h: 6 * Copyright (C) 1999 Hewlett-Packard Co 7 * Copyright (C) 1999 David Mosberger-Tang <davidm@hpl.hp.com> 8 * 9 * 10 * Generic C version of 64bit/32bit division and modulo, with 11 * 64bit result and 32bit remainder. 12 * 13 * The fast case for (n>>32 == 0) is handled inline by do_div(). 14 * 15 * Code generated for this function might be very inefficient 16 * for some CPUs. __div64_32() can be overridden by linking arch-specific 17 * assembly versions such as arch/ppc/lib/div64.S and arch/sh/lib/div64.S 18 * or by defining a preprocessor macro in arch/include/asm/div64.h. 19 */ 20 21#include <linux/bitops.h> 22#include <linux/export.h> 23#include <linux/math.h> 24#include <linux/math64.h> 25#include <linux/log2.h> 26 27/* Not needed on 64bit architectures */ 28#if BITS_PER_LONG == 32 29 30#ifndef __div64_32 31uint32_t __attribute__((weak)) __div64_32(uint64_t *n, uint32_t base) 32{ 33 uint64_t rem = *n; 34 uint64_t b = base; 35 uint64_t res, d = 1; 36 uint32_t high = rem >> 32; 37 38 /* Reduce the thing a bit first */ 39 res = 0; 40 if (high >= base) { 41 high /= base; 42 res = (uint64_t) high << 32; 43 rem -= (uint64_t) (high*base) << 32; 44 } 45 46 while ((int64_t)b > 0 && b < rem) { 47 b = b+b; 48 d = d+d; 49 } 50 51 do { 52 if (rem >= b) { 53 rem -= b; 54 res += d; 55 } 56 b >>= 1; 57 d >>= 1; 58 } while (d); 59 60 *n = res; 61 return rem; 62} 63EXPORT_SYMBOL(__div64_32); 64#endif 65 66#ifndef div_s64_rem 67s64 div_s64_rem(s64 dividend, s32 divisor, s32 *remainder) 68{ 69 u64 quotient; 70 71 if (dividend < 0) { 72 quotient = div_u64_rem(-dividend, abs(divisor), (u32 *)remainder); 73 *remainder = -*remainder; 74 if (divisor > 0) 75 quotient = -quotient; 76 } else { 77 quotient = div_u64_rem(dividend, abs(divisor), (u32 *)remainder); 78 if (divisor < 0) 79 quotient = -quotient; 80 } 81 return quotient; 82} 83EXPORT_SYMBOL(div_s64_rem); 84#endif 85 86/* 87 * div64_u64_rem - unsigned 64bit divide with 64bit divisor and remainder 88 * @dividend: 64bit dividend 89 * @divisor: 64bit divisor 90 * @remainder: 64bit remainder 91 * 92 * This implementation is a comparable to algorithm used by div64_u64. 93 * But this operation, which includes math for calculating the remainder, 94 * is kept distinct to avoid slowing down the div64_u64 operation on 32bit 95 * systems. 96 */ 97#ifndef div64_u64_rem 98u64 div64_u64_rem(u64 dividend, u64 divisor, u64 *remainder) 99{ 100 u32 high = divisor >> 32; 101 u64 quot; 102 103 if (high == 0) { 104 u32 rem32; 105 quot = div_u64_rem(dividend, divisor, &rem32); 106 *remainder = rem32; 107 } else { 108 int n = fls(high); 109 quot = div_u64(dividend >> n, divisor >> n); 110 111 if (quot != 0) 112 quot--; 113 114 *remainder = dividend - quot * divisor; 115 if (*remainder >= divisor) { 116 quot++; 117 *remainder -= divisor; 118 } 119 } 120 121 return quot; 122} 123EXPORT_SYMBOL(div64_u64_rem); 124#endif 125 126/* 127 * div64_u64 - unsigned 64bit divide with 64bit divisor 128 * @dividend: 64bit dividend 129 * @divisor: 64bit divisor 130 * 131 * This implementation is a modified version of the algorithm proposed 132 * by the book 'Hacker's Delight'. The original source and full proof 133 * can be found here and is available for use without restriction. 134 * 135 * 'http://www.hackersdelight.org/hdcodetxt/divDouble.c.txt' 136 */ 137#ifndef div64_u64 138u64 div64_u64(u64 dividend, u64 divisor) 139{ 140 u32 high = divisor >> 32; 141 u64 quot; 142 143 if (high == 0) { 144 quot = div_u64(dividend, divisor); 145 } else { 146 int n = fls(high); 147 quot = div_u64(dividend >> n, divisor >> n); 148 149 if (quot != 0) 150 quot--; 151 if ((dividend - quot * divisor) >= divisor) 152 quot++; 153 } 154 155 return quot; 156} 157EXPORT_SYMBOL(div64_u64); 158#endif 159 160#ifndef div64_s64 161s64 div64_s64(s64 dividend, s64 divisor) 162{ 163 s64 quot, t; 164 165 quot = div64_u64(abs(dividend), abs(divisor)); 166 t = (dividend ^ divisor) >> 63; 167 168 return (quot ^ t) - t; 169} 170EXPORT_SYMBOL(div64_s64); 171#endif 172 173#endif /* BITS_PER_LONG == 32 */ 174 175/* 176 * Iterative div/mod for use when dividend is not expected to be much 177 * bigger than divisor. 178 */ 179u32 iter_div_u64_rem(u64 dividend, u32 divisor, u64 *remainder) 180{ 181 return __iter_div_u64_rem(dividend, divisor, remainder); 182} 183EXPORT_SYMBOL(iter_div_u64_rem); 184 185#ifndef mul_u64_u64_div_u64 186u64 mul_u64_u64_div_u64(u64 a, u64 b, u64 c) 187{ 188 u64 res = 0, div, rem; 189 int shift; 190 191 /* can a * b overflow ? */ 192 if (ilog2(a) + ilog2(b) > 62) { 193 /* 194 * (b * a) / c is equal to 195 * 196 * (b / c) * a + 197 * (b % c) * a / c 198 * 199 * if nothing overflows. Can the 1st multiplication 200 * overflow? Yes, but we do not care: this can only 201 * happen if the end result can't fit in u64 anyway. 202 * 203 * So the code below does 204 * 205 * res = (b / c) * a; 206 * b = b % c; 207 */ 208 div = div64_u64_rem(b, c, &rem); 209 res = div * a; 210 b = rem; 211 212 shift = ilog2(a) + ilog2(b) - 62; 213 if (shift > 0) { 214 /* drop precision */ 215 b >>= shift; 216 c >>= shift; 217 if (!c) 218 return res; 219 } 220 } 221 222 return res + div64_u64(a * b, c); 223} 224EXPORT_SYMBOL(mul_u64_u64_div_u64); 225#endif 226