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 <[email protected]> 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() is, in C++ notation, observing that the name 12 * is a function-like macro and the n parameter has the semantics of a C++ 13 * reference: 14 * 15 * uint32_t do_div(uint64_t &n, uint32_t base) 16 * { 17 * uint32_t remainder = n % base; 18 * n = n / base; 19 * return remainder; 20 * } 21 * 22 * NOTE: macro parameter n is evaluated multiple times, 23 * beware of side effects! 24 */ 25 26 #include <linux/types.h> 27 #include <linux/compiler.h> 28 29 #if BITS_PER_LONG == 64 30 31 /** 32 * do_div - returns 2 values: calculate remainder and update new dividend 33 * @n: uint64_t dividend (will be updated) 34 * @base: uint32_t divisor 35 * 36 * Summary: 37 * ``uint32_t remainder = n % base;`` 38 * ``n = n / base;`` 39 * 40 * Return: (uint32_t)remainder 41 * 42 * NOTE: macro parameter @n is evaluated multiple times, 43 * beware of side effects! 44 */ 45 # define do_div(n,base) ({ \ 46 uint32_t __base = (base); \ 47 uint32_t __rem; \ 48 __rem = ((uint64_t)(n)) % __base; \ 49 (n) = ((uint64_t)(n)) / __base; \ 50 __rem; \ 51 }) 52 53 #elif BITS_PER_LONG == 32 54 55 #include <linux/log2.h> 56 57 /* 58 * If the divisor happens to be constant, we determine the appropriate 59 * inverse at compile time to turn the division into a few inline 60 * multiplications which ought to be much faster. 61 * 62 * (It is unfortunate that gcc doesn't perform all this internally.) 63 */ 64 65 #define __div64_const32(n, ___b) \ 66 ({ \ 67 /* \ 68 * Multiplication by reciprocal of b: n / b = n * (p / b) / p \ 69 * \ 70 * We rely on the fact that most of this code gets optimized \ 71 * away at compile time due to constant propagation and only \ 72 * a few multiplication instructions should remain. \ 73 * Hence this monstrous macro (static inline doesn't always \ 74 * do the trick here). \ 75 */ \ 76 uint64_t ___res, ___x, ___t, ___m, ___n = (n); \ 77 uint32_t ___p; \ 78 bool ___bias = false; \ 79 \ 80 /* determine MSB of b */ \ 81 ___p = 1 << ilog2(___b); \ 82 \ 83 /* compute m = ((p << 64) + b - 1) / b */ \ 84 ___m = (~0ULL / ___b) * ___p; \ 85 ___m += (((~0ULL % ___b + 1) * ___p) + ___b - 1) / ___b; \ 86 \ 87 /* one less than the dividend with highest result */ \ 88 ___x = ~0ULL / ___b * ___b - 1; \ 89 \ 90 /* test our ___m with res = m * x / (p << 64) */ \ 91 ___res = (___m & 0xffffffff) * (___x & 0xffffffff); \ 92 ___t = (___m & 0xffffffff) * (___x >> 32) + (___res >> 32); \ 93 ___res = (___m >> 32) * (___x >> 32) + (___t >> 32); \ 94 ___t = (___m >> 32) * (___x & 0xffffffff) + (___t & 0xffffffff);\ 95 ___res = (___res + (___t >> 32)) / ___p; \ 96 \ 97 /* Now validate what we've got. */ \ 98 if (___res != ___x / ___b) { \ 99 /* \ 100 * We can't get away without a bias to compensate \ 101 * for bit truncation errors. To avoid it we'd need an \ 102 * additional bit to represent m which would overflow \ 103 * a 64-bit variable. \ 104 * \ 105 * Instead we do m = p / b and n / b = (n * m + m) / p. \ 106 */ \ 107 ___bias = true; \ 108 /* Compute m = (p << 64) / b */ \ 109 ___m = (~0ULL / ___b) * ___p; \ 110 ___m += ((~0ULL % ___b + 1) * ___p) / ___b; \ 111 } \ 112 \ 113 /* Reduce m / p to help avoid overflow handling later. */ \ 114 ___p /= (___m & -___m); \ 115 ___m /= (___m & -___m); \ 116 \ 117 /* \ 118 * Perform (m_bias + m * n) / (1 << 64). \ 119 * From now on there will be actual runtime code generated. \ 120 */ \ 121 ___res = __arch_xprod_64(___m, ___n, ___bias); \ 122 \ 123 ___res /= ___p; \ 124 }) 125 126 #ifndef __arch_xprod_64 127 /* 128 * Default C implementation for __arch_xprod_64() 129 * 130 * Prototype: uint64_t __arch_xprod_64(const uint64_t m, uint64_t n, bool bias) 131 * Semantic: retval = ((bias ? m : 0) + m * n) >> 64 132 * 133 * The product is a 128-bit value, scaled down to 64 bits. 134 * Hoping for compile-time optimization of conditional code. 135 * Architectures may provide their own optimized assembly implementation. 136 */ 137 static inline uint64_t __arch_xprod_64(const uint64_t m, uint64_t n, bool bias) 138 { 139 uint32_t m_lo = m; 140 uint32_t m_hi = m >> 32; 141 uint32_t n_lo = n; 142 uint32_t n_hi = n >> 32; 143 uint64_t x, y; 144 145 /* Determine if overflow handling can be dispensed with. */ 146 bool no_ovf = __builtin_constant_p(m) && 147 ((m >> 32) + (m & 0xffffffff) < 0x100000000); 148 149 if (no_ovf) { 150 x = (uint64_t)m_lo * n_lo + (bias ? m : 0); 151 x >>= 32; 152 x += (uint64_t)m_lo * n_hi; 153 x += (uint64_t)m_hi * n_lo; 154 x >>= 32; 155 x += (uint64_t)m_hi * n_hi; 156 } else { 157 x = (uint64_t)m_lo * n_lo + (bias ? m_lo : 0); 158 y = (uint64_t)m_lo * n_hi + (uint32_t)(x >> 32) + (bias ? m_hi : 0); 159 x = (uint64_t)m_hi * n_hi + (uint32_t)(y >> 32); 160 y = (uint64_t)m_hi * n_lo + (uint32_t)y; 161 x += (uint32_t)(y >> 32); 162 } 163 164 return x; 165 } 166 #endif 167 168 #ifndef __div64_32 169 extern uint32_t __div64_32(uint64_t *dividend, uint32_t divisor); 170 #endif 171 172 /* The unnecessary pointer compare is there 173 * to check for type safety (n must be 64bit) 174 */ 175 # define do_div(n,base) ({ \ 176 uint32_t __base = (base); \ 177 uint32_t __rem; \ 178 (void)(((typeof((n)) *)0) == ((uint64_t *)0)); \ 179 if (__builtin_constant_p(__base) && \ 180 is_power_of_2(__base)) { \ 181 __rem = (n) & (__base - 1); \ 182 (n) >>= ilog2(__base); \ 183 } else if (__builtin_constant_p(__base) && \ 184 __base != 0) { \ 185 uint32_t __res_lo, __n_lo = (n); \ 186 (n) = __div64_const32(n, __base); \ 187 /* the remainder can be computed with 32-bit regs */ \ 188 __res_lo = (n); \ 189 __rem = __n_lo - __res_lo * __base; \ 190 } else if (likely(((n) >> 32) == 0)) { \ 191 __rem = (uint32_t)(n) % __base; \ 192 (n) = (uint32_t)(n) / __base; \ 193 } else { \ 194 __rem = __div64_32(&(n), __base); \ 195 } \ 196 __rem; \ 197 }) 198 199 #else /* BITS_PER_LONG == ?? */ 200 201 # error do_div() does not yet support the C64 202 203 #endif /* BITS_PER_LONG */ 204 205 #endif /* _ASM_GENERIC_DIV64_H */ 206