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-rw-r--r--src/ext/hg64.c327
1 files changed, 327 insertions, 0 deletions
diff --git a/src/ext/hg64.c b/src/ext/hg64.c
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+++ b/src/ext/hg64.c
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+/*
+ * hg64 - 64-bit histograms
+ *
+ * Written by Tony Finch <dot@dotat.at> <fanf@isc.org>
+ *
+ * Copyright (C) Internet Systems Consortium, Inc. ("ISC")
+ *
+ * SPDX-License-Identifier: MPL-2.0
+ *
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, you can obtain one at https://mozilla.org/MPL/2.0/.
+ */
+
+#include <assert.h>
+#include <errno.h>
+#include <stdatomic.h>
+#include <stdbool.h>
+#include <stdint.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+
+#include "hg64.h"
+
+/* number of bins is same as number of bits in a value */
+#define BINS 64
+
+typedef atomic_uint_fast64_t counter;
+typedef _Atomic(counter*) bin_ptr;
+
+struct hg64 {
+ unsigned sigbits;
+ bin_ptr bin[BINS];
+};
+
+static inline counter*
+get_bin(hg64* hg, unsigned b)
+{
+ /* key_to_new_counter() below has the matching store / release */
+ return (atomic_load_explicit(&hg->bin[b], memory_order_acquire));
+}
+
+/*
+ * when we only care about the histogram precision
+ */
+struct hg64p {
+ unsigned sigbits;
+};
+
+#ifdef __has_attribute
+#if __has_attribute(__transparent_union__)
+#define TRANSPARENT __attribute__((__transparent_union__))
+#endif
+#endif
+
+#ifdef TRANSPARENT
+
+typedef union hg64u {
+ hg64* hg;
+ const struct hg64p* hp;
+} hg64u TRANSPARENT;
+
+#define hg64p(hu) ((hu).hp)
+#else
+
+typedef void* hg64u;
+
+#define hg64p(hu) ((const struct hg64p*)(hu))
+#endif
+
+/*
+ * The bins arrays have a static size for simplicity, but that means We
+ * waste a little extra space that could be saved by omitting the
+ * exponents that land in the denormal number bin. The following macros
+ * calculate (at run time) the exact number of keys when we need to do
+ * accurate bounds checks.
+ */
+#define DENORMALS(hp) ((hp)->sigbits - 1)
+#define EXPONENTS(hp) (BINS - DENORMALS(hp))
+#define MANTISSAS(hp) (1 << (hp)->sigbits)
+#define KEYS(hp) (EXPONENTS(hp) * MANTISSAS(hp))
+
+#define BINSIZE(hp) MANTISSAS(hp)
+
+/**********************************************************************/
+
+#define OUTARG(ptr, val) (void)(((ptr) != NULL) && (bool)(*(ptr) = (val)))
+
+/**********************************************************************/
+
+hg64* hg64_create(unsigned sigbits)
+{
+ if (sigbits < 1 || 15 < sigbits) {
+ return (NULL);
+ }
+ hg64* hg = malloc(sizeof(*hg));
+ hg->sigbits = sigbits;
+ /*
+ * it is probably portable to zero-initialize atomics but the
+ * C standard says we shouldn't rely on it; but this loop
+ * should optimize to memset() on most target systems
+ */
+ for (unsigned b = 0; b < BINS; b++) {
+ atomic_init(&hg->bin[b], NULL);
+ }
+ return (hg);
+}
+
+void hg64_destroy(hg64* hg)
+{
+ for (unsigned b = 0; b < BINS; b++) {
+ free(get_bin(hg, b));
+ }
+ *hg = (hg64) { 0 };
+ free(hg);
+}
+
+/**********************************************************************/
+
+static inline uint64_t
+key_to_minval(hg64u hu, unsigned key)
+{
+ unsigned binsize = BINSIZE(hg64p(hu));
+ unsigned exponent = (key / binsize) - 1;
+ uint64_t mantissa = (key % binsize) + binsize;
+ return (key < binsize ? key : mantissa << exponent);
+}
+
+/*
+ * don't shift by 64, and don't underflow exponent; instead,
+ * reduce shift by 1 for each hazard and pre-shift UINT64_MAX
+ */
+static inline uint64_t
+key_to_maxval(hg64u hu, unsigned key)
+{
+ unsigned binsize = BINSIZE(hg64p(hu));
+ unsigned shift = 63 - (key / binsize);
+ uint64_t range = UINT64_MAX / 4 >> shift;
+ return (key_to_minval(hu, key) + range);
+}
+
+/*
+ * This branchless conversion is due to Paul Khuong: see bin_down_of() in
+ * https://pvk.ca/Blog/2015/06/27/linear-log-bucketing-fast-versatile-simple/
+ */
+static inline unsigned
+value_to_key(hg64u hu, uint64_t value)
+{
+ /* fast path */
+ const struct hg64p* hp = hg64p(hu);
+ /* ensure that denormal numbers are all in the same bin */
+ uint64_t binned = value | BINSIZE(hp);
+ int clz = __builtin_clzll((unsigned long long)(binned));
+ /* actually 1 less than the exponent except for denormals */
+ unsigned exponent = 63 - hp->sigbits - clz;
+ /* mantissa has leading bit set except for denormals */
+ unsigned mantissa = value >> exponent;
+ /* leading bit of mantissa adds one to exponent */
+ return ((exponent << hp->sigbits) + mantissa);
+}
+
+static counter*
+key_to_new_counter(hg64* hg, unsigned key)
+{
+ /* slow path */
+ unsigned binsize = BINSIZE(hg);
+ unsigned b = key / binsize;
+ unsigned c = key % binsize;
+ counter* old_bp = NULL;
+ counter* new_bp = malloc(sizeof(counter) * binsize);
+ /* see comment in hg64_create() above */
+ for (unsigned i = 0; i < binsize; i++) {
+ atomic_init(new_bp + i, 0);
+ }
+ bin_ptr* bpp = &hg->bin[b];
+ if (atomic_compare_exchange_strong_explicit(bpp, &old_bp, new_bp,
+ memory_order_acq_rel, memory_order_acquire)) {
+ return (new_bp + c);
+ } else {
+ /* lost the race, so use the winner's counters */
+ free(new_bp);
+ return (old_bp + c);
+ }
+}
+
+static inline counter*
+key_to_counter(hg64* hg, unsigned key)
+{
+ /* fast path */
+ unsigned binsize = BINSIZE(hg);
+ unsigned b = key / binsize;
+ unsigned c = key % binsize;
+ counter* bp = get_bin(hg, b);
+ return (bp == NULL ? NULL : bp + c);
+}
+
+static inline uint64_t
+get_key_count(hg64* hg, unsigned key)
+{
+ counter* ctr = key_to_counter(hg, key);
+ return (ctr == NULL ? 0 : atomic_load_explicit(ctr, memory_order_relaxed));
+}
+
+static inline void
+add_key_count(hg64* hg, unsigned key, uint64_t inc)
+{
+ if (inc == 0)
+ return;
+ counter* ctr = key_to_counter(hg, key);
+ ctr = ctr ? ctr : key_to_new_counter(hg, key);
+ atomic_fetch_add_explicit(ctr, inc, memory_order_relaxed);
+}
+
+/**********************************************************************/
+
+void hg64_inc(hg64* hg, uint64_t value)
+{
+ add_key_count(hg, value_to_key(hg, value), 1);
+}
+
+bool hg64_get(hg64* hg, unsigned key,
+ uint64_t* pmin, uint64_t* pmax, uint64_t* pcount)
+{
+ if (key < KEYS(hg)) {
+ OUTARG(pmin, key_to_minval(hg, key));
+ OUTARG(pmax, key_to_maxval(hg, key));
+ OUTARG(pcount, get_key_count(hg, key));
+ return (true);
+ } else {
+ return (false);
+ }
+}
+
+unsigned
+hg64_next(hg64* hg, unsigned key)
+{
+ key++;
+ while (key < KEYS(hg) && (key & (BINSIZE(hg) - 1)) == 0 && key_to_counter(hg, key) == NULL) {
+ key += BINSIZE(hg);
+ }
+ return (key);
+}
+
+/*
+ * https://fanf2.user.srcf.net/hermes/doc/antiforgery/stats.pdf
+ */
+void hg64_mean_variance(hg64* hg, double* pmean, double* pvar)
+{
+ double pop = 0.0;
+ double mean = 0.0;
+ double sigma = 0.0;
+ uint64_t min, max, count;
+ for (unsigned key = 0;
+ hg64_get(hg, key, &min, &max, &count);
+ key = hg64_next(hg, key)) {
+ double delta = (double)min / 2.0 + (double)max / 2.0 - mean;
+ if (count != 0) { /* avoid division by zero */
+ pop += count;
+ mean += count * delta / pop;
+ sigma += count * delta * (min + max - mean);
+ }
+ }
+ OUTARG(pmean, mean);
+ OUTARG(pvar, sigma / pop);
+}
+
+/**********************************************************************/
+
+void hg64_merge(hg64* target, hg64* source)
+{
+ uint64_t count;
+ for (unsigned skey = 0;
+ hg64_get(source, skey, NULL, NULL, &count);
+ skey = hg64_next(source, skey)) {
+ uint64_t svmin = key_to_minval(source, skey);
+ uint64_t svmax = key_to_maxval(source, skey);
+ unsigned tkmin = value_to_key(target, svmin);
+ unsigned tkmax = value_to_key(target, svmax);
+ unsigned keys = tkmax - tkmin + 1;
+ /* is there a more cunning way to spread out the remainder? */
+ uint64_t div = count / keys;
+ uint64_t rem = count % keys;
+ for (unsigned tkey = tkmin; tkey <= tkmax; tkey++) {
+ uint64_t inc = div + (uint64_t)(tkey < rem);
+ add_key_count(target, tkey, inc);
+ }
+ }
+}
+
+void hg64_diff(hg64* a, hg64* b, hg64* diff)
+{
+ assert((a->sigbits == b->sigbits) && (b->sigbits == diff->sigbits));
+ uint64_t count_a = 0;
+ uint64_t count_b = 0;
+ for (unsigned key = 0;
+ hg64_get(a, key, NULL, NULL, &count_a);
+ key++) {
+ hg64_get(b, key, NULL, NULL, &count_b);
+ add_key_count(diff, key, count_a - count_b);
+ }
+}
+
+unsigned hg64_min_key(hg64* hg)
+{
+ uint64_t pcount;
+ for (unsigned key = 0;
+ hg64_get(hg, key, NULL, NULL, &pcount);
+ key = hg64_next(hg, key)) {
+ if (pcount > 0)
+ return key;
+ }
+ return 0;
+}
+
+unsigned hg64_max_key(hg64* hg)
+{
+ unsigned last_key = 0;
+ uint64_t pcount;
+ for (unsigned key = 0;
+ hg64_get(hg, key, NULL, NULL, &pcount);
+ key = hg64_next(hg, key)) {
+ if (pcount > 0)
+ last_key = key;
+ }
+ return last_key;
+}
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