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/export.h> 22 #include <linux/kernel.h> 23 #include <linux/math64.h> 24 25 /* Not needed on 64bit architectures */ 26 #if BITS_PER_LONG == 32 27 28 #ifndef __div64_32 29 uint32_t __attribute__((weak)) __div64_32(uint64_t *n, uint32_t base) 30 { 31 uint64_t rem = *n; 32 uint64_t b = base; 33 uint64_t res, d = 1; 34 uint32_t high = rem >> 32; 35 36 /* Reduce the thing a bit first */ 37 res = 0; 38 if (high >= base) { 39 high /= base; 40 res = (uint64_t) high << 32; 41 rem -= (uint64_t) (high*base) << 32; 42 } 43 44 while ((int64_t)b > 0 && b < rem) { 45 b = b+b; 46 d = d+d; 47 } 48 49 do { 50 if (rem >= b) { 51 rem -= b; 52 res += d; 53 } 54 b >>= 1; 55 d >>= 1; 56 } while (d); 57 58 *n = res; 59 return rem; 60 } 61 EXPORT_SYMBOL(__div64_32); 62 #endif 63 64 /** 65 * div_s64_rem - signed 64bit divide with 64bit divisor and remainder 66 * @dividend: 64bit dividend 67 * @divisor: 64bit divisor 68 * @remainder: 64bit remainder 69 */ 70 #ifndef div_s64_rem 71 s64 div_s64_rem(s64 dividend, s32 divisor, s32 *remainder) 72 { 73 u64 quotient; 74 75 if (dividend < 0) { 76 quotient = div_u64_rem(-dividend, abs(divisor), (u32 *)remainder); 77 *remainder = -*remainder; 78 if (divisor > 0) 79 quotient = -quotient; 80 } else { 81 quotient = div_u64_rem(dividend, abs(divisor), (u32 *)remainder); 82 if (divisor < 0) 83 quotient = -quotient; 84 } 85 return quotient; 86 } 87 EXPORT_SYMBOL(div_s64_rem); 88 #endif 89 90 /** 91 * div64_u64_rem - unsigned 64bit divide with 64bit divisor and remainder 92 * @dividend: 64bit dividend 93 * @divisor: 64bit divisor 94 * @remainder: 64bit remainder 95 * 96 * This implementation is a comparable to algorithm used by div64_u64. 97 * But this operation, which includes math for calculating the remainder, 98 * is kept distinct to avoid slowing down the div64_u64 operation on 32bit 99 * systems. 100 */ 101 #ifndef div64_u64_rem 102 u64 div64_u64_rem(u64 dividend, u64 divisor, u64 *remainder) 103 { 104 u32 high = divisor >> 32; 105 u64 quot; 106 107 if (high == 0) { 108 u32 rem32; 109 quot = div_u64_rem(dividend, divisor, &rem32); 110 *remainder = rem32; 111 } else { 112 int n = fls(high); 113 quot = div_u64(dividend >> n, divisor >> n); 114 115 if (quot != 0) 116 quot--; 117 118 *remainder = dividend - quot * divisor; 119 if (*remainder >= divisor) { 120 quot++; 121 *remainder -= divisor; 122 } 123 } 124 125 return quot; 126 } 127 EXPORT_SYMBOL(div64_u64_rem); 128 #endif 129 130 /** 131 * div64_u64 - unsigned 64bit divide with 64bit divisor 132 * @dividend: 64bit dividend 133 * @divisor: 64bit divisor 134 * 135 * This implementation is a modified version of the algorithm proposed 136 * by the book 'Hacker's Delight'. The original source and full proof 137 * can be found here and is available for use without restriction. 138 * 139 * 'http://www.hackersdelight.org/hdcodetxt/divDouble.c.txt' 140 */ 141 #ifndef div64_u64 142 u64 div64_u64(u64 dividend, u64 divisor) 143 { 144 u32 high = divisor >> 32; 145 u64 quot; 146 147 if (high == 0) { 148 quot = div_u64(dividend, divisor); 149 } else { 150 int n = fls(high); 151 quot = div_u64(dividend >> n, divisor >> n); 152 153 if (quot != 0) 154 quot--; 155 if ((dividend - quot * divisor) >= divisor) 156 quot++; 157 } 158 159 return quot; 160 } 161 EXPORT_SYMBOL(div64_u64); 162 #endif 163 164 /** 165 * div64_s64 - signed 64bit divide with 64bit divisor 166 * @dividend: 64bit dividend 167 * @divisor: 64bit divisor 168 */ 169 #ifndef div64_s64 170 s64 div64_s64(s64 dividend, s64 divisor) 171 { 172 s64 quot, t; 173 174 quot = div64_u64(abs(dividend), abs(divisor)); 175 t = (dividend ^ divisor) >> 63; 176 177 return (quot ^ t) - t; 178 } 179 EXPORT_SYMBOL(div64_s64); 180 #endif 181 182 #endif /* BITS_PER_LONG == 32 */ 183 184 /* 185 * Iterative div/mod for use when dividend is not expected to be much 186 * bigger than divisor. 187 */ 188 u32 iter_div_u64_rem(u64 dividend, u32 divisor, u64 *remainder) 189 { 190 return __iter_div_u64_rem(dividend, divisor, remainder); 191 } 192 EXPORT_SYMBOL(iter_div_u64_rem); 193 194 #ifndef mul_u64_u64_div_u64 195 u64 mul_u64_u64_div_u64(u64 a, u64 b, u64 c) 196 { 197 u64 res = 0, div, rem; 198 int shift; 199 200 /* can a * b overflow ? */ 201 if (ilog2(a) + ilog2(b) > 62) { 202 /* 203 * (b * a) / c is equal to 204 * 205 * (b / c) * a + 206 * (b % c) * a / c 207 * 208 * if nothing overflows. Can the 1st multiplication 209 * overflow? Yes, but we do not care: this can only 210 * happen if the end result can't fit in u64 anyway. 211 * 212 * So the code below does 213 * 214 * res = (b / c) * a; 215 * b = b % c; 216 */ 217 div = div64_u64_rem(b, c, &rem); 218 res = div * a; 219 b = rem; 220 221 shift = ilog2(a) + ilog2(b) - 62; 222 if (shift > 0) { 223 /* drop precision */ 224 b >>= shift; 225 c >>= shift; 226 if (!c) 227 return res; 228 } 229 } 230 231 return res + div64_u64(a * b, c); 232 } 233 #endif 234