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() 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#ifdef CONFIG_CC_OPTIMIZE_FOR_PERFORMANCE
138static __always_inline
139#else
140static inline
141#endif
142uint64_t __arch_xprod_64(const uint64_t m, uint64_t n, bool bias)
143{
144 uint32_t m_lo = m;
145 uint32_t m_hi = m >> 32;
146 uint32_t n_lo = n;
147 uint32_t n_hi = n >> 32;
148 uint64_t x, y;
149
150 /* Determine if overflow handling can be dispensed with. */
151 bool no_ovf = __builtin_constant_p(m) &&
152 ((m >> 32) + (m & 0xffffffff) < 0x100000000);
153
154 if (no_ovf) {
155 x = (uint64_t)m_lo * n_lo + (bias ? m : 0);
156 x >>= 32;
157 x += (uint64_t)m_lo * n_hi;
158 x += (uint64_t)m_hi * n_lo;
159 x >>= 32;
160 x += (uint64_t)m_hi * n_hi;
161 } else {
162 x = (uint64_t)m_lo * n_lo + (bias ? m_lo : 0);
163 y = (uint64_t)m_lo * n_hi + (uint32_t)(x >> 32) + (bias ? m_hi : 0);
164 x = (uint64_t)m_hi * n_hi + (uint32_t)(y >> 32);
165 y = (uint64_t)m_hi * n_lo + (uint32_t)y;
166 x += (uint32_t)(y >> 32);
167 }
168
169 return x;
170}
171#endif
172
173#ifndef __div64_32
174extern uint32_t __div64_32(uint64_t *dividend, uint32_t divisor);
175#endif
176
177/* The unnecessary pointer compare is there
178 * to check for type safety (n must be 64bit)
179 */
180# define do_div(n,base) ({ \
181 uint32_t __base = (base); \
182 uint32_t __rem; \
183 (void)(((typeof((n)) *)0) == ((uint64_t *)0)); \
184 if (__builtin_constant_p(__base) && \
185 is_power_of_2(__base)) { \
186 __rem = (n) & (__base - 1); \
187 (n) >>= ilog2(__base); \
188 } else if (__builtin_constant_p(__base) && \
189 __base != 0) { \
190 uint32_t __res_lo, __n_lo = (n); \
191 (n) = __div64_const32(n, __base); \
192 /* the remainder can be computed with 32-bit regs */ \
193 __res_lo = (n); \
194 __rem = __n_lo - __res_lo * __base; \
195 } else if (likely(((n) >> 32) == 0)) { \
196 __rem = (uint32_t)(n) % __base; \
197 (n) = (uint32_t)(n) / __base; \
198 } else { \
199 __rem = __div64_32(&(n), __base); \
200 } \
201 __rem; \
202 })
203
204#else /* BITS_PER_LONG == ?? */
205
206# error do_div() does not yet support the C64
207
208#endif /* BITS_PER_LONG */
209
210#endif /* _ASM_GENERIC_DIV64_H */
211

source code of linux/include/asm-generic/div64.h