Add vendoring

vendor/github.com/valyala/histogram/LICENSE

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+The MIT License (MIT)
+
+Copyright (c) 2019 Aliaksandr Valialkin
+
+Permission is hereby granted, free of charge, to any person obtaining a copy
+of this software and associated documentation files (the "Software"), to deal
+in the Software without restriction, including without limitation the rights
+to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+copies of the Software, and to permit persons to whom the Software is
+furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in all
+copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+SOFTWARE.

vendor/github.com/valyala/histogram/README.md

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+[![GoDoc](https://godoc.org/github.com/valyala/histogram?status.svg)](http://godoc.org/github.com/valyala/histogram)
+[![Go Report](https://goreportcard.com/badge/github.com/valyala/histogram)](https://goreportcard.com/report/github.com/valyala/histogram)
+
+
+# histogram
+
+Fast histograms for Go.
+
+See [docs](https://godoc.org/github.com/valyala/histogram).

vendor/github.com/valyala/histogram/histogram.go

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+// Package histogram provides building blocks for fast histograms.
+package histogram
+
+import (
+	"math"
+	"sort"
+	"sync"
+
+	"github.com/valyala/fastrand"
+)
+
+var (
+	infNeg = math.Inf(-1)
+	infPos = math.Inf(1)
+	nan    = math.NaN()
+)
+
+// Fast is a fast histogram.
+//
+// It cannot be used from concurrently running goroutines without
+// external synchronization.
+type Fast struct {
+	max   float64
+	min   float64
+	count uint64
+
+	a   []float64
+	tmp []float64
+	rng fastrand.RNG
+}
+
+// NewFast returns new fast histogram.
+func NewFast() *Fast {
+	f := &Fast{}
+	f.Reset()
+	return f
+}
+
+// Reset resets the histogram.
+func (f *Fast) Reset() {
+	f.max = infNeg
+	f.min = infPos
+	f.count = 0
+	if len(f.a) > 0 {
+		f.a = f.a[:0]
+		f.tmp = f.tmp[:0]
+	} else {
+		// Free up memory occupied by unused histogram.
+		f.a = nil
+		f.tmp = nil
+	}
+	// Reset rng state in order to get repeatable results
+	// for the same sequence of values passed to Fast.Update.
+	// See https://github.com/VictoriaMetrics/VictoriaMetrics/issues/1612
+	f.rng.Seed(1)
+}
+
+// Update updates the f with v.
+func (f *Fast) Update(v float64) {
+	if v > f.max {
+		f.max = v
+	}
+	if v < f.min {
+		f.min = v
+	}
+
+	f.count++
+	if len(f.a) < maxSamples {
+		f.a = append(f.a, v)
+		return
+	}
+	if n := int(f.rng.Uint32n(uint32(f.count))); n < len(f.a) {
+		f.a[n] = v
+	}
+}
+
+const maxSamples = 1000
+
+// Quantile returns the quantile value for the given phi.
+func (f *Fast) Quantile(phi float64) float64 {
+	f.tmp = append(f.tmp[:0], f.a...)
+	sort.Float64s(f.tmp)
+	return f.quantile(phi)
+}
+
+// Quantiles appends quantile values to dst for the given phis.
+func (f *Fast) Quantiles(dst, phis []float64) []float64 {
+	f.tmp = append(f.tmp[:0], f.a...)
+	sort.Float64s(f.tmp)
+	for _, phi := range phis {
+		q := f.quantile(phi)
+		dst = append(dst, q)
+	}
+	return dst
+}
+
+func (f *Fast) quantile(phi float64) float64 {
+	if len(f.tmp) == 0 || math.IsNaN(phi) {
+		return nan
+	}
+	if phi <= 0 {
+		return f.min
+	}
+	if phi >= 1 {
+		return f.max
+	}
+	idx := uint(phi*float64(len(f.tmp)-1) + 0.5)
+	if idx >= uint(len(f.tmp)) {
+		idx = uint(len(f.tmp) - 1)
+	}
+	return f.tmp[idx]
+}
+
+// GetFast returns a histogram from a pool.
+func GetFast() *Fast {
+	v := fastPool.Get()
+	if v == nil {
+		return NewFast()
+	}
+	return v.(*Fast)
+}
+
+// PutFast puts hf to the pool.
+//
+// hf cannot be used after this call.
+func PutFast(f *Fast) {
+	f.Reset()
+	fastPool.Put(f)
+}
+
+var fastPool sync.Pool