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