1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
|
/* SPDX-License-Identifier: GPL-2.0 */
#ifndef _ASM_GENERIC_DIV64_H
#define _ASM_GENERIC_DIV64_H
/*
* Copyright (C) 2003 Bernardo Innocenti <bernie@develer.com>
* Based on former asm-ppc/div64.h and asm-m68knommu/div64.h
*
* Optimization for constant divisors on 32-bit machines:
* Copyright (C) 2006-2015 Nicolas Pitre
*
* The semantics of do_div() is, in C++ notation, observing that the name
* is a function-like macro and the n parameter has the semantics of a C++
* reference:
*
* uint32_t do_div(uint64_t &n, uint32_t base)
* {
* uint32_t remainder = n % base;
* n = n / base;
* return remainder;
* }
*
* NOTE: macro parameter n is evaluated multiple times,
* beware of side effects!
*/
#include <linux/types.h>
#include <linux/compiler.h>
#if BITS_PER_LONG == 64
/**
* do_div - returns 2 values: calculate remainder and update new dividend
* @n: uint64_t dividend (will be updated)
* @base: uint32_t divisor
*
* Summary:
* ``uint32_t remainder = n % base;``
* ``n = n / base;``
*
* Return: (uint32_t)remainder
*
* NOTE: macro parameter @n is evaluated multiple times,
* beware of side effects!
*/
# define do_div(n,base) ({ \
uint32_t __base = (base); \
uint32_t __rem; \
__rem = ((uint64_t)(n)) % __base; \
(n) = ((uint64_t)(n)) / __base; \
__rem; \
})
#elif BITS_PER_LONG == 32
#include <linux/log2.h>
/*
* If the divisor happens to be constant, we determine the appropriate
* inverse at compile time to turn the division into a few inline
* multiplications which ought to be much faster.
*
* (It is unfortunate that gcc doesn't perform all this internally.)
*/
#define __div64_const32(n, ___b) \
({ \
/* \
* Multiplication by reciprocal of b: n / b = n * (p / b) / p \
* \
* We rely on the fact that most of this code gets optimized \
* away at compile time due to constant propagation and only \
* a few multiplication instructions should remain. \
* Hence this monstrous macro (static inline doesn't always \
* do the trick here). \
*/ \
uint64_t ___res, ___x, ___t, ___m, ___n = (n); \
uint32_t ___p; \
bool ___bias = false; \
\
/* determine MSB of b */ \
___p = 1 << ilog2(___b); \
\
/* compute m = ((p << 64) + b - 1) / b */ \
___m = (~0ULL / ___b) * ___p; \
___m += (((~0ULL % ___b + 1) * ___p) + ___b - 1) / ___b; \
\
/* one less than the dividend with highest result */ \
___x = ~0ULL / ___b * ___b - 1; \
\
/* test our ___m with res = m * x / (p << 64) */ \
___res = (___m & 0xffffffff) * (___x & 0xffffffff); \
___t = (___m & 0xffffffff) * (___x >> 32) + (___res >> 32); \
___res = (___m >> 32) * (___x >> 32) + (___t >> 32); \
___t = (___m >> 32) * (___x & 0xffffffff) + (___t & 0xffffffff);\
___res = (___res + (___t >> 32)) / ___p; \
\
/* Now validate what we've got. */ \
if (___res != ___x / ___b) { \
/* \
* We can't get away without a bias to compensate \
* for bit truncation errors. To avoid it we'd need an \
* additional bit to represent m which would overflow \
* a 64-bit variable. \
* \
* Instead we do m = p / b and n / b = (n * m + m) / p. \
*/ \
___bias = true; \
/* Compute m = (p << 64) / b */ \
___m = (~0ULL / ___b) * ___p; \
___m += ((~0ULL % ___b + 1) * ___p) / ___b; \
} \
\
/* Reduce m / p to help avoid overflow handling later. */ \
___p /= (___m & -___m); \
___m /= (___m & -___m); \
\
/* \
* Perform (m_bias + m * n) / (1 << 64). \
* From now on there will be actual runtime code generated. \
*/ \
___res = __arch_xprod_64(___m, ___n, ___bias); \
\
___res /= ___p; \
})
#ifndef __arch_xprod_64
/*
* Default C implementation for __arch_xprod_64()
*
* Prototype: uint64_t __arch_xprod_64(const uint64_t m, uint64_t n, bool bias)
* Semantic: retval = ((bias ? m : 0) + m * n) >> 64
*
* The product is a 128-bit value, scaled down to 64 bits.
* Hoping for compile-time optimization of conditional code.
* Architectures may provide their own optimized assembly implementation.
*/
#ifdef CONFIG_CC_OPTIMIZE_FOR_PERFORMANCE
static __always_inline
#else
static inline
#endif
uint64_t __arch_xprod_64(const uint64_t m, uint64_t n, bool bias)
{
uint32_t m_lo = m;
uint32_t m_hi = m >> 32;
uint32_t n_lo = n;
uint32_t n_hi = n >> 32;
uint64_t x, y;
/* Determine if overflow handling can be dispensed with. */
bool no_ovf = __builtin_constant_p(m) &&
((m >> 32) + (m & 0xffffffff) < 0x100000000);
if (no_ovf) {
x = (uint64_t)m_lo * n_lo + (bias ? m : 0);
x >>= 32;
x += (uint64_t)m_lo * n_hi;
x += (uint64_t)m_hi * n_lo;
x >>= 32;
x += (uint64_t)m_hi * n_hi;
} else {
x = (uint64_t)m_lo * n_lo + (bias ? m_lo : 0);
y = (uint64_t)m_lo * n_hi + (uint32_t)(x >> 32) + (bias ? m_hi : 0);
x = (uint64_t)m_hi * n_hi + (uint32_t)(y >> 32);
y = (uint64_t)m_hi * n_lo + (uint32_t)y;
x += (uint32_t)(y >> 32);
}
return x;
}
#endif
#ifndef __div64_32
extern uint32_t __div64_32(uint64_t *dividend, uint32_t divisor);
#endif
/* The unnecessary pointer compare is there
* to check for type safety (n must be 64bit)
*/
# define do_div(n,base) ({ \
uint32_t __base = (base); \
uint32_t __rem; \
(void)(((typeof((n)) *)0) == ((uint64_t *)0)); \
if (__builtin_constant_p(__base) && \
is_power_of_2(__base)) { \
__rem = (n) & (__base - 1); \
(n) >>= ilog2(__base); \
} else if (__builtin_constant_p(__base) && \
__base != 0) { \
uint32_t __res_lo, __n_lo = (n); \
(n) = __div64_const32(n, __base); \
/* the remainder can be computed with 32-bit regs */ \
__res_lo = (n); \
__rem = __n_lo - __res_lo * __base; \
} else if (likely(((n) >> 32) == 0)) { \
__rem = (uint32_t)(n) % __base; \
(n) = (uint32_t)(n) / __base; \
} else { \
__rem = __div64_32(&(n), __base); \
} \
__rem; \
})
#else /* BITS_PER_LONG == ?? */
# error do_div() does not yet support the C64
#endif /* BITS_PER_LONG */
#endif /* _ASM_GENERIC_DIV64_H */
|
