1 /* SPDX-License-Identifier: GPL-2.0 */ 2 #ifndef _ASM_GENERIC_DIV64_H 3 #define _ASM_GENERIC_DIV64_H 4 /* 5 * Copyright (C) 2003 Bernardo Innocenti <bernie@develer.com> 6 * Based on former asm-ppc/div64.h and asm-m68knommu/div64.h 7 * 8 * Optimization for constant divisors on 32-bit machines: 9 * Copyright (C) 2006-2015 Nicolas Pitre 10 * 11 * The semantics of do_div() are: 12 * 13 * uint32_t do_div(uint64_t *n, uint32_t base) 14 * { 15 * uint32_t remainder = *n % base; 16 * *n = *n / base; 17 * return remainder; 18 * } 19 * 20 * NOTE: macro parameter n is evaluated multiple times, 21 * beware of side effects! 22 */ 23 24 #include <linux/types.h> 25 #include <linux/compiler.h> 26 27 #if BITS_PER_LONG == 64 28 29 /** 30 * do_div - returns 2 values: calculate remainder and update new dividend 31 * @n: uint64_t dividend (will be updated) 32 * @base: uint32_t divisor 33 * 34 * Summary: 35 * ``uint32_t remainder = n % base;`` 36 * ``n = n / base;`` 37 * 38 * Return: (uint32_t)remainder 39 * 40 * NOTE: macro parameter @n is evaluated multiple times, 41 * beware of side effects! 42 */ 43 # define do_div(n,base) ({ \ 44 uint32_t __base = (base); \ 45 uint32_t __rem; \ 46 __rem = ((uint64_t)(n)) % __base; \ 47 (n) = ((uint64_t)(n)) / __base; \ 48 __rem; \ 49 }) 50 51 #elif BITS_PER_LONG == 32 52 53 #include <linux/log2.h> 54 55 /* 56 * If the divisor happens to be constant, we determine the appropriate 57 * inverse at compile time to turn the division into a few inline 58 * multiplications which ought to be much faster. And yet only if compiling 59 * with a sufficiently recent gcc version to perform proper 64-bit constant 60 * propagation. 61 * 62 * (It is unfortunate that gcc doesn't perform all this internally.) 63 */ 64 65 #ifndef __div64_const32_is_OK 66 #define __div64_const32_is_OK (__GNUC__ >= 4) 67 #endif 68 69 #define __div64_const32(n, ___b) \ 70 ({ \ 71 /* \ 72 * Multiplication by reciprocal of b: n / b = n * (p / b) / p \ 73 * \ 74 * We rely on the fact that most of this code gets optimized \ 75 * away at compile time due to constant propagation and only \ 76 * a few multiplication instructions should remain. \ 77 * Hence this monstrous macro (static inline doesn't always \ 78 * do the trick here). \ 79 */ \ 80 uint64_t ___res, ___x, ___t, ___m, ___n = (n); \ 81 uint32_t ___p, ___bias; \ 82 \ 83 /* determine MSB of b */ \ 84 ___p = 1 << ilog2(___b); \ 85 \ 86 /* compute m = ((p << 64) + b - 1) / b */ \ 87 ___m = (~0ULL / ___b) * ___p; \ 88 ___m += (((~0ULL % ___b + 1) * ___p) + ___b - 1) / ___b; \ 89 \ 90 /* one less than the dividend with highest result */ \ 91 ___x = ~0ULL / ___b * ___b - 1; \ 92 \ 93 /* test our ___m with res = m * x / (p << 64) */ \ 94 ___res = ((___m & 0xffffffff) * (___x & 0xffffffff)) >> 32; \ 95 ___t = ___res += (___m & 0xffffffff) * (___x >> 32); \ 96 ___res += (___x & 0xffffffff) * (___m >> 32); \ 97 ___t = (___res < ___t) ? (1ULL << 32) : 0; \ 98 ___res = (___res >> 32) + ___t; \ 99 ___res += (___m >> 32) * (___x >> 32); \ 100 ___res /= ___p; \ 101 \ 102 /* Now sanitize and optimize what we've got. */ \ 103 if (~0ULL % (___b / (___b & -___b)) == 0) { \ 104 /* special case, can be simplified to ... */ \ 105 ___n /= (___b & -___b); \ 106 ___m = ~0ULL / (___b / (___b & -___b)); \ 107 ___p = 1; \ 108 ___bias = 1; \ 109 } else if (___res != ___x / ___b) { \ 110 /* \ 111 * We can't get away without a bias to compensate \ 112 * for bit truncation errors. To avoid it we'd need an \ 113 * additional bit to represent m which would overflow \ 114 * a 64-bit variable. \ 115 * \ 116 * Instead we do m = p / b and n / b = (n * m + m) / p. \ 117 */ \ 118 ___bias = 1; \ 119 /* Compute m = (p << 64) / b */ \ 120 ___m = (~0ULL / ___b) * ___p; \ 121 ___m += ((~0ULL % ___b + 1) * ___p) / ___b; \ 122 } else { \ 123 /* \ 124 * Reduce m / p, and try to clear bit 31 of m when \ 125 * possible, otherwise that'll need extra overflow \ 126 * handling later. \ 127 */ \ 128 uint32_t ___bits = -(___m & -___m); \ 129 ___bits |= ___m >> 32; \ 130 ___bits = (~___bits) << 1; \ 131 /* \ 132 * If ___bits == 0 then setting bit 31 is unavoidable. \ 133 * Simply apply the maximum possible reduction in that \ 134 * case. Otherwise the MSB of ___bits indicates the \ 135 * best reduction we should apply. \ 136 */ \ 137 if (!___bits) { \ 138 ___p /= (___m & -___m); \ 139 ___m /= (___m & -___m); \ 140 } else { \ 141 ___p >>= ilog2(___bits); \ 142 ___m >>= ilog2(___bits); \ 143 } \ 144 /* No bias needed. */ \ 145 ___bias = 0; \ 146 } \ 147 \ 148 /* \ 149 * Now we have a combination of 2 conditions: \ 150 * \ 151 * 1) whether or not we need to apply a bias, and \ 152 * \ 153 * 2) whether or not there might be an overflow in the cross \ 154 * product determined by (___m & ((1 << 63) | (1 << 31))). \ 155 * \ 156 * Select the best way to do (m_bias + m * n) / (1 << 64). \ 157 * From now on there will be actual runtime code generated. \ 158 */ \ 159 ___res = __arch_xprod_64(___m, ___n, ___bias); \ 160 \ 161 ___res /= ___p; \ 162 }) 163 164 #ifndef __arch_xprod_64 165 /* 166 * Default C implementation for __arch_xprod_64() 167 * 168 * Prototype: uint64_t __arch_xprod_64(const uint64_t m, uint64_t n, bool bias) 169 * Semantic: retval = ((bias ? m : 0) + m * n) >> 64 170 * 171 * The product is a 128-bit value, scaled down to 64 bits. 172 * Assuming constant propagation to optimize away unused conditional code. 173 * Architectures may provide their own optimized assembly implementation. 174 */ 175 static inline uint64_t __arch_xprod_64(const uint64_t m, uint64_t n, bool bias) 176 { 177 uint32_t m_lo = m; 178 uint32_t m_hi = m >> 32; 179 uint32_t n_lo = n; 180 uint32_t n_hi = n >> 32; 181 uint64_t res; 182 uint32_t res_lo, res_hi, tmp; 183 184 if (!bias) { 185 res = ((uint64_t)m_lo * n_lo) >> 32; 186 } else if (!(m & ((1ULL << 63) | (1ULL << 31)))) { 187 /* there can't be any overflow here */ 188 res = (m + (uint64_t)m_lo * n_lo) >> 32; 189 } else { 190 res = m + (uint64_t)m_lo * n_lo; 191 res_lo = res >> 32; 192 res_hi = (res_lo < m_hi); 193 res = res_lo | ((uint64_t)res_hi << 32); 194 } 195 196 if (!(m & ((1ULL << 63) | (1ULL << 31)))) { 197 /* there can't be any overflow here */ 198 res += (uint64_t)m_lo * n_hi; 199 res += (uint64_t)m_hi * n_lo; 200 res >>= 32; 201 } else { 202 res += (uint64_t)m_lo * n_hi; 203 tmp = res >> 32; 204 res += (uint64_t)m_hi * n_lo; 205 res_lo = res >> 32; 206 res_hi = (res_lo < tmp); 207 res = res_lo | ((uint64_t)res_hi << 32); 208 } 209 210 res += (uint64_t)m_hi * n_hi; 211 212 return res; 213 } 214 #endif 215 216 #ifndef __div64_32 217 extern uint32_t __div64_32(uint64_t *dividend, uint32_t divisor); 218 #endif 219 220 /* The unnecessary pointer compare is there 221 * to check for type safety (n must be 64bit) 222 */ 223 # define do_div(n,base) ({ \ 224 uint32_t __base = (base); \ 225 uint32_t __rem; \ 226 (void)(((typeof((n)) *)0) == ((uint64_t *)0)); \ 227 if (__builtin_constant_p(__base) && \ 228 is_power_of_2(__base)) { \ 229 __rem = (n) & (__base - 1); \ 230 (n) >>= ilog2(__base); \ 231 } else if (__div64_const32_is_OK && \ 232 __builtin_constant_p(__base) && \ 233 __base != 0) { \ 234 uint32_t __res_lo, __n_lo = (n); \ 235 (n) = __div64_const32(n, __base); \ 236 /* the remainder can be computed with 32-bit regs */ \ 237 __res_lo = (n); \ 238 __rem = __n_lo - __res_lo * __base; \ 239 } else if (likely(((n) >> 32) == 0)) { \ 240 __rem = (uint32_t)(n) % __base; \ 241 (n) = (uint32_t)(n) / __base; \ 242 } else \ 243 __rem = __div64_32(&(n), __base); \ 244 __rem; \ 245 }) 246 247 #else /* BITS_PER_LONG == ?? */ 248 249 # error do_div() does not yet support the C64 250 251 #endif /* BITS_PER_LONG */ 252 253 #endif /* _ASM_GENERIC_DIV64_H */ 254