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 31 uint32_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 } 63 EXPORT_SYMBOL(__div64_32); 64 #endif 65 66 /** 67 * div_s64_rem - signed 64bit divide with 64bit divisor and remainder 68 * @dividend: 64bit dividend 69 * @divisor: 64bit divisor 70 * @remainder: 64bit remainder 71 */ 72 #ifndef div_s64_rem 73 s64 div_s64_rem(s64 dividend, s32 divisor, s32 *remainder) 74 { 75 u64 quotient; 76 77 if (dividend < 0) { 78 quotient = div_u64_rem(-dividend, abs(divisor), (u32 *)remainder); 79 *remainder = -*remainder; 80 if (divisor > 0) 81 quotient = -quotient; 82 } else { 83 quotient = div_u64_rem(dividend, abs(divisor), (u32 *)remainder); 84 if (divisor < 0) 85 quotient = -quotient; 86 } 87 return quotient; 88 } 89 EXPORT_SYMBOL(div_s64_rem); 90 #endif 91 92 /** 93 * div64_u64_rem - unsigned 64bit divide with 64bit divisor and remainder 94 * @dividend: 64bit dividend 95 * @divisor: 64bit divisor 96 * @remainder: 64bit remainder 97 * 98 * This implementation is a comparable to algorithm used by div64_u64. 99 * But this operation, which includes math for calculating the remainder, 100 * is kept distinct to avoid slowing down the div64_u64 operation on 32bit 101 * systems. 102 */ 103 #ifndef div64_u64_rem 104 u64 div64_u64_rem(u64 dividend, u64 divisor, u64 *remainder) 105 { 106 u32 high = divisor >> 32; 107 u64 quot; 108 109 if (high == 0) { 110 u32 rem32; 111 quot = div_u64_rem(dividend, divisor, &rem32); 112 *remainder = rem32; 113 } else { 114 int n = fls(high); 115 quot = div_u64(dividend >> n, divisor >> n); 116 117 if (quot != 0) 118 quot--; 119 120 *remainder = dividend - quot * divisor; 121 if (*remainder >= divisor) { 122 quot++; 123 *remainder -= divisor; 124 } 125 } 126 127 return quot; 128 } 129 EXPORT_SYMBOL(div64_u64_rem); 130 #endif 131 132 /** 133 * div64_u64 - unsigned 64bit divide with 64bit divisor 134 * @dividend: 64bit dividend 135 * @divisor: 64bit divisor 136 * 137 * This implementation is a modified version of the algorithm proposed 138 * by the book 'Hacker's Delight'. The original source and full proof 139 * can be found here and is available for use without restriction. 140 * 141 * 'http://www.hackersdelight.org/hdcodetxt/divDouble.c.txt' 142 */ 143 #ifndef div64_u64 144 u64 div64_u64(u64 dividend, u64 divisor) 145 { 146 u32 high = divisor >> 32; 147 u64 quot; 148 149 if (high == 0) { 150 quot = div_u64(dividend, divisor); 151 } else { 152 int n = fls(high); 153 quot = div_u64(dividend >> n, divisor >> n); 154 155 if (quot != 0) 156 quot--; 157 if ((dividend - quot * divisor) >= divisor) 158 quot++; 159 } 160 161 return quot; 162 } 163 EXPORT_SYMBOL(div64_u64); 164 #endif 165 166 /** 167 * div64_s64 - signed 64bit divide with 64bit divisor 168 * @dividend: 64bit dividend 169 * @divisor: 64bit divisor 170 */ 171 #ifndef div64_s64 172 s64 div64_s64(s64 dividend, s64 divisor) 173 { 174 s64 quot, t; 175 176 quot = div64_u64(abs(dividend), abs(divisor)); 177 t = (dividend ^ divisor) >> 63; 178 179 return (quot ^ t) - t; 180 } 181 EXPORT_SYMBOL(div64_s64); 182 #endif 183 184 #endif /* BITS_PER_LONG == 32 */ 185 186 /* 187 * Iterative div/mod for use when dividend is not expected to be much 188 * bigger than divisor. 189 */ 190 u32 iter_div_u64_rem(u64 dividend, u32 divisor, u64 *remainder) 191 { 192 return __iter_div_u64_rem(dividend, divisor, remainder); 193 } 194 EXPORT_SYMBOL(iter_div_u64_rem); 195 196 #ifndef mul_u64_u64_div_u64 197 u64 mul_u64_u64_div_u64(u64 a, u64 b, u64 c) 198 { 199 u64 res = 0, div, rem; 200 int shift; 201 202 /* can a * b overflow ? */ 203 if (ilog2(a) + ilog2(b) > 62) { 204 /* 205 * (b * a) / c is equal to 206 * 207 * (b / c) * a + 208 * (b % c) * a / c 209 * 210 * if nothing overflows. Can the 1st multiplication 211 * overflow? Yes, but we do not care: this can only 212 * happen if the end result can't fit in u64 anyway. 213 * 214 * So the code below does 215 * 216 * res = (b / c) * a; 217 * b = b % c; 218 */ 219 div = div64_u64_rem(b, c, &rem); 220 res = div * a; 221 b = rem; 222 223 shift = ilog2(a) + ilog2(b) - 62; 224 if (shift > 0) { 225 /* drop precision */ 226 b >>= shift; 227 c >>= shift; 228 if (!c) 229 return res; 230 } 231 } 232 233 return res + div64_u64(a * b, c); 234 } 235 #endif 236