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