summaryrefslogtreecommitdiff
path: root/fs/bcachefs/mean_and_variance.h
blob: b2be565bb8f214bc2ac4ebd6efac324ac20b7241 (plain)
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
/* SPDX-License-Identifier: GPL-2.0 */
#ifndef MEAN_AND_VARIANCE_H_
#define MEAN_AND_VARIANCE_H_

#include <linux/types.h>
#include <linux/limits.h>
#include <linux/math.h>
#include <linux/math64.h>

#define SQRT_U64_MAX 4294967295ULL

/*
 * u128_u: u128 user mode, because not all architectures support a real int128
 * type
 *
 * We don't use this version in userspace, because in userspace we link with
 * Rust and rustc has issues with u128.
 */

#if defined(__SIZEOF_INT128__) && defined(__KERNEL__)

typedef struct {
	unsigned __int128 v;
} __aligned(16) u128_u;

static inline u128_u u64_to_u128(u64 a)
{
	return (u128_u) { .v = a };
}

static inline u64 u128_lo(u128_u a)
{
	return a.v;
}

static inline u64 u128_hi(u128_u a)
{
	return a.v >> 64;
}

static inline u128_u u128_add(u128_u a, u128_u b)
{
	a.v += b.v;
	return a;
}

static inline u128_u u128_sub(u128_u a, u128_u b)
{
	a.v -= b.v;
	return a;
}

static inline u128_u u128_shl(u128_u a, s8 shift)
{
	a.v <<= shift;
	return a;
}

static inline u128_u u128_square(u64 a)
{
	u128_u b = u64_to_u128(a);

	b.v *= b.v;
	return b;
}

#else

typedef struct {
	u64 hi, lo;
} __aligned(16) u128_u;

/* conversions */

static inline u128_u u64_to_u128(u64 a)
{
	return (u128_u) { .lo = a };
}

static inline u64 u128_lo(u128_u a)
{
	return a.lo;
}

static inline u64 u128_hi(u128_u a)
{
	return a.hi;
}

/* arithmetic */

static inline u128_u u128_add(u128_u a, u128_u b)
{
	u128_u c;

	c.lo = a.lo + b.lo;
	c.hi = a.hi + b.hi + (c.lo < a.lo);
	return c;
}

static inline u128_u u128_sub(u128_u a, u128_u b)
{
	u128_u c;

	c.lo = a.lo - b.lo;
	c.hi = a.hi - b.hi - (c.lo > a.lo);
	return c;
}

static inline u128_u u128_shl(u128_u i, s8 shift)
{
	u128_u r;

	r.lo = i.lo << shift;
	if (shift < 64)
		r.hi = (i.hi << shift) | (i.lo >> (64 - shift));
	else {
		r.hi = i.lo << (shift - 64);
		r.lo = 0;
	}
	return r;
}

static inline u128_u u128_square(u64 i)
{
	u128_u r;
	u64  h = i >> 32, l = i & U32_MAX;

	r =             u128_shl(u64_to_u128(h*h), 64);
	r = u128_add(r, u128_shl(u64_to_u128(h*l), 32));
	r = u128_add(r, u128_shl(u64_to_u128(l*h), 32));
	r = u128_add(r,          u64_to_u128(l*l));
	return r;
}

#endif

static inline u128_u u64s_to_u128(u64 hi, u64 lo)
{
	u128_u c = u64_to_u128(hi);

	c = u128_shl(c, 64);
	c = u128_add(c, u64_to_u128(lo));
	return c;
}

u128_u u128_div(u128_u n, u64 d);

struct mean_and_variance {
	s64	n;
	s64	sum;
	u128_u	sum_squares;
};

/* expontentially weighted variant */
struct mean_and_variance_weighted {
	bool	init;
	u8	weight;	/* base 2 logarithim */
	s64	mean;
	u64	variance;
};

/**
 * fast_divpow2() - fast approximation for n / (1 << d)
 * @n: numerator
 * @d: the power of 2 denominator.
 *
 * note: this rounds towards 0.
 */
static inline s64 fast_divpow2(s64 n, u8 d)
{
	return (n + ((n < 0) ? ((1 << d) - 1) : 0)) >> d;
}

/**
 * mean_and_variance_update() - update a mean_and_variance struct @s1 with a new sample @v1
 * and return it.
 * @s1: the mean_and_variance to update.
 * @v1: the new sample.
 *
 * see linked pdf equation 12.
 */
static inline void
mean_and_variance_update(struct mean_and_variance *s, s64 v)
{
	s->n++;
	s->sum += v;
	s->sum_squares = u128_add(s->sum_squares, u128_square(abs(v)));
}

s64 mean_and_variance_get_mean(struct mean_and_variance s);
u64 mean_and_variance_get_variance(struct mean_and_variance s1);
u32 mean_and_variance_get_stddev(struct mean_and_variance s);

void mean_and_variance_weighted_update(struct mean_and_variance_weighted *s, s64 v);

s64 mean_and_variance_weighted_get_mean(struct mean_and_variance_weighted s);
u64 mean_and_variance_weighted_get_variance(struct mean_and_variance_weighted s);
u32 mean_and_variance_weighted_get_stddev(struct mean_and_variance_weighted s);

#endif // MEAN_AND_VAIRANCE_H_