Update bcachefs sources to 50847e296b34 bcachefs: Check subvol <-> inode pointers...

[bcachefs-tools-debian] / include / linux / mean_and_variance.h

diff --git a/include/linux/mean_and_variance.h b/include/linux/mean_and_variance.h
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+++ b/include/linux/mean_and_variance.h
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+/* 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__) && !defined(CONFIG_PARISC)
+
+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 {
+       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, bool initted, u8 weight);
+
+s64 mean_and_variance_weighted_get_mean(struct mean_and_variance_weighted s,
+               u8 weight);
+u64 mean_and_variance_weighted_get_variance(struct mean_and_variance_weighted s,
+               u8 weight);
+u32 mean_and_variance_weighted_get_stddev(struct mean_and_variance_weighted s,
+               u8 weight);
+
+#endif // MEAN_AND_VAIRANCE_H_