prometheus/storage/buffer.go
Nathan Baulch 50cd453c8f
Some checks failed
buf.build / lint and publish (push) Waiting to run
CI / Go tests (push) Waiting to run
CI / More Go tests (push) Waiting to run
CI / Go tests with previous Go version (push) Waiting to run
CI / UI tests (push) Waiting to run
CI / Go tests on Windows (push) Waiting to run
CI / Mixins tests (push) Waiting to run
CI / Build Prometheus for common architectures (0) (push) Waiting to run
CI / Build Prometheus for common architectures (1) (push) Waiting to run
CI / Build Prometheus for common architectures (2) (push) Waiting to run
CI / Build Prometheus for all architectures (0) (push) Waiting to run
CI / Build Prometheus for all architectures (1) (push) Waiting to run
CI / Build Prometheus for all architectures (10) (push) Waiting to run
CI / Build Prometheus for all architectures (11) (push) Waiting to run
CI / Build Prometheus for all architectures (2) (push) Waiting to run
CI / Build Prometheus for all architectures (3) (push) Waiting to run
CI / Build Prometheus for all architectures (4) (push) Waiting to run
CI / Build Prometheus for all architectures (5) (push) Waiting to run
CI / Build Prometheus for all architectures (6) (push) Waiting to run
CI / Build Prometheus for all architectures (7) (push) Waiting to run
CI / Build Prometheus for all architectures (8) (push) Waiting to run
CI / Build Prometheus for all architectures (9) (push) Waiting to run
CI / Report status of build Prometheus for all architectures (push) Blocked by required conditions
CI / Check generated parser (push) Waiting to run
CI / golangci-lint (push) Waiting to run
CI / fuzzing (push) Waiting to run
CI / codeql (push) Waiting to run
CI / Publish main branch artifacts (push) Blocked by required conditions
CI / Publish release artefacts (push) Blocked by required conditions
CI / Publish UI on npm Registry (push) Blocked by required conditions
Scorecards supply-chain security / Scorecards analysis (push) Waiting to run
Push README to Docker Hub / Push README to Docker Hub (push) Has been cancelled
Push README to Docker Hub / Push README to quay.io (push) Has been cancelled
chore: Fix typos (#14868)
* Fix typos

---------

Signed-off-by: Nathan Baulch <nathan.baulch@gmail.com>
2024-09-10 22:32:03 +02:00

859 lines
20 KiB
Go

// Copyright 2017 The Prometheus Authors
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
package storage
import (
"fmt"
"math"
"github.com/prometheus/prometheus/model/histogram"
"github.com/prometheus/prometheus/tsdb/chunkenc"
"github.com/prometheus/prometheus/tsdb/chunks"
)
// BufferedSeriesIterator wraps an iterator with a look-back buffer.
type BufferedSeriesIterator struct {
hReader histogram.Histogram
fhReader histogram.FloatHistogram
it chunkenc.Iterator
buf *sampleRing
delta int64
lastTime int64
valueType chunkenc.ValueType
}
// NewBuffer returns a new iterator that buffers the values within the time range
// of the current element and the duration of delta before, initialized with an
// empty iterator. Use Reset() to set an actual iterator to be buffered.
func NewBuffer(delta int64) *BufferedSeriesIterator {
return NewBufferIterator(chunkenc.NewNopIterator(), delta)
}
// NewBufferIterator returns a new iterator that buffers the values within the
// time range of the current element and the duration of delta before.
func NewBufferIterator(it chunkenc.Iterator, delta int64) *BufferedSeriesIterator {
bit := &BufferedSeriesIterator{
buf: newSampleRing(delta, 0, chunkenc.ValNone),
delta: delta,
}
bit.Reset(it)
return bit
}
// Reset re-uses the buffer with a new iterator, resetting the buffered time
// delta to its original value.
func (b *BufferedSeriesIterator) Reset(it chunkenc.Iterator) {
b.it = it
b.lastTime = math.MinInt64
b.buf.reset()
b.buf.delta = b.delta
b.valueType = it.Next()
}
// ReduceDelta lowers the buffered time delta, for the current SeriesIterator only.
func (b *BufferedSeriesIterator) ReduceDelta(delta int64) bool {
return b.buf.reduceDelta(delta)
}
// PeekBack returns the nth previous element of the iterator. If there is none buffered,
// ok is false.
func (b *BufferedSeriesIterator) PeekBack(n int) (sample chunks.Sample, ok bool) {
return b.buf.nthLast(n)
}
// Buffer returns an iterator over the buffered data. Invalidates previously
// returned iterators.
func (b *BufferedSeriesIterator) Buffer() *SampleRingIterator {
return b.buf.iterator()
}
// Seek advances the iterator to the element at time t or greater.
func (b *BufferedSeriesIterator) Seek(t int64) chunkenc.ValueType {
t0 := t - b.buf.delta
// If the delta would cause us to seek backwards, preserve the buffer
// and just continue regular advancement while filling the buffer on the way.
if b.valueType != chunkenc.ValNone && t0 > b.lastTime {
b.buf.reset()
b.valueType = b.it.Seek(t0)
switch b.valueType {
case chunkenc.ValNone:
return chunkenc.ValNone
case chunkenc.ValFloat, chunkenc.ValHistogram, chunkenc.ValFloatHistogram:
b.lastTime = b.AtT()
default:
panic(fmt.Errorf("BufferedSeriesIterator: unknown value type %v", b.valueType))
}
}
if b.lastTime >= t {
return b.valueType
}
for {
if b.valueType = b.Next(); b.valueType == chunkenc.ValNone || b.lastTime >= t {
return b.valueType
}
}
}
// Next advances the iterator to the next element.
func (b *BufferedSeriesIterator) Next() chunkenc.ValueType {
// Add current element to buffer before advancing.
switch b.valueType {
case chunkenc.ValNone:
return chunkenc.ValNone
case chunkenc.ValFloat:
t, f := b.it.At()
b.buf.addF(fSample{t: t, f: f})
case chunkenc.ValHistogram:
t, h := b.it.AtHistogram(&b.hReader)
b.buf.addH(hSample{t: t, h: h})
case chunkenc.ValFloatHistogram:
t, fh := b.it.AtFloatHistogram(&b.fhReader)
b.buf.addFH(fhSample{t: t, fh: fh})
default:
panic(fmt.Errorf("BufferedSeriesIterator: unknown value type %v", b.valueType))
}
b.valueType = b.it.Next()
if b.valueType != chunkenc.ValNone {
b.lastTime = b.AtT()
}
return b.valueType
}
// At returns the current float element of the iterator.
func (b *BufferedSeriesIterator) At() (int64, float64) {
return b.it.At()
}
// AtHistogram returns the current histogram element of the iterator.
func (b *BufferedSeriesIterator) AtHistogram(fh *histogram.Histogram) (int64, *histogram.Histogram) {
return b.it.AtHistogram(fh)
}
// AtFloatHistogram returns the current float-histogram element of the iterator.
func (b *BufferedSeriesIterator) AtFloatHistogram(fh *histogram.FloatHistogram) (int64, *histogram.FloatHistogram) {
return b.it.AtFloatHistogram(fh)
}
// AtT returns the current timestamp of the iterator.
func (b *BufferedSeriesIterator) AtT() int64 {
return b.it.AtT()
}
// Err returns the last encountered error.
func (b *BufferedSeriesIterator) Err() error {
return b.it.Err()
}
type fSample struct {
t int64
f float64
}
func (s fSample) T() int64 {
return s.t
}
func (s fSample) F() float64 {
return s.f
}
func (s fSample) H() *histogram.Histogram {
panic("H() called for fSample")
}
func (s fSample) FH() *histogram.FloatHistogram {
panic("FH() called for fSample")
}
func (s fSample) Type() chunkenc.ValueType {
return chunkenc.ValFloat
}
type hSample struct {
t int64
h *histogram.Histogram
}
func (s hSample) T() int64 {
return s.t
}
func (s hSample) F() float64 {
panic("F() called for hSample")
}
func (s hSample) H() *histogram.Histogram {
return s.h
}
func (s hSample) FH() *histogram.FloatHistogram {
return s.h.ToFloat(nil)
}
func (s hSample) Type() chunkenc.ValueType {
return chunkenc.ValHistogram
}
type fhSample struct {
t int64
fh *histogram.FloatHistogram
}
func (s fhSample) T() int64 {
return s.t
}
func (s fhSample) F() float64 {
panic("F() called for fhSample")
}
func (s fhSample) H() *histogram.Histogram {
panic("H() called for fhSample")
}
func (s fhSample) FH() *histogram.FloatHistogram {
return s.fh
}
func (s fhSample) Type() chunkenc.ValueType {
return chunkenc.ValFloatHistogram
}
type sampleRing struct {
delta int64
// Lookback buffers. We use iBuf for mixed samples, but one of the three
// concrete ones for homogeneous samples. (Only one of the four bufs is
// allowed to be populated!) This avoids the overhead of the interface
// wrapper for the happy (and by far most common) case of homogeneous
// samples.
iBuf []chunks.Sample
fBuf []fSample
hBuf []hSample
fhBuf []fhSample
bufInUse bufType
i int // Position of most recent element in ring buffer.
f int // Position of first element in ring buffer.
l int // Number of elements in buffer.
it SampleRingIterator
}
type bufType int
const (
noBuf bufType = iota // Nothing yet stored in sampleRing.
iBuf
fBuf
hBuf
fhBuf
)
// newSampleRing creates a new sampleRing. If you do not know the preferred
// value type yet, use a size of 0 (in which case the provided typ doesn't
// matter). On the first add, a buffer of size 16 will be allocated with the
// preferred type being the type of the first added sample.
func newSampleRing(delta int64, size int, typ chunkenc.ValueType) *sampleRing {
r := &sampleRing{delta: delta}
r.reset()
if size <= 0 {
// Will initialize on first add.
return r
}
switch typ {
case chunkenc.ValFloat:
r.fBuf = make([]fSample, size)
case chunkenc.ValHistogram:
r.hBuf = make([]hSample, size)
case chunkenc.ValFloatHistogram:
r.fhBuf = make([]fhSample, size)
default:
// Do not initialize anything because the 1st sample will be
// added to one of the other bufs anyway.
}
return r
}
func (r *sampleRing) reset() {
r.l = 0
r.i = -1
r.f = 0
r.bufInUse = noBuf
// The first sample after the reset will always go to a specialized
// buffer. If we later need to change to the interface buffer, we'll
// copy from the specialized buffer to the interface buffer. For that to
// work properly, we have to reset the interface buffer here, too.
r.iBuf = r.iBuf[:0]
}
// Resets and returns the iterator. Invalidates previously returned iterators.
func (r *sampleRing) iterator() *SampleRingIterator {
r.it.reset(r)
return &r.it
}
// SampleRingIterator is returned by BufferedSeriesIterator.Buffer() and can be
// used to iterate samples buffered in the lookback window.
type SampleRingIterator struct {
r *sampleRing
i int
t int64
f float64
h *histogram.Histogram
fh *histogram.FloatHistogram
}
func (it *SampleRingIterator) reset(r *sampleRing) {
it.r = r
it.i = -1
it.h = nil
it.fh = nil
}
func (it *SampleRingIterator) Next() chunkenc.ValueType {
it.i++
if it.i >= it.r.l {
return chunkenc.ValNone
}
switch it.r.bufInUse {
case fBuf:
s := it.r.atF(it.i)
it.t = s.t
it.f = s.f
return chunkenc.ValFloat
case hBuf:
s := it.r.atH(it.i)
it.t = s.t
it.h = s.h
return chunkenc.ValHistogram
case fhBuf:
s := it.r.atFH(it.i)
it.t = s.t
it.fh = s.fh
return chunkenc.ValFloatHistogram
}
s := it.r.at(it.i)
it.t = s.T()
switch s.Type() {
case chunkenc.ValHistogram:
it.h = s.H()
it.fh = nil
return chunkenc.ValHistogram
case chunkenc.ValFloatHistogram:
it.fh = s.FH()
it.h = nil
return chunkenc.ValFloatHistogram
default:
it.f = s.F()
return chunkenc.ValFloat
}
}
// At returns the current float element of the iterator.
func (it *SampleRingIterator) At() (int64, float64) {
return it.t, it.f
}
// AtHistogram returns the current histogram element of the iterator.
func (it *SampleRingIterator) AtHistogram() (int64, *histogram.Histogram) {
return it.t, it.h
}
// AtFloatHistogram returns the current histogram element of the iterator. If the
// current sample is an integer histogram, it will be converted to a float histogram.
// An optional histogram.FloatHistogram can be provided to avoid allocating a new
// object for the conversion.
func (it *SampleRingIterator) AtFloatHistogram(fh *histogram.FloatHistogram) (int64, *histogram.FloatHistogram) {
if it.fh == nil {
return it.t, it.h.ToFloat(fh)
}
if fh != nil {
it.fh.CopyTo(fh)
return it.t, fh
}
return it.t, it.fh.Copy()
}
func (it *SampleRingIterator) AtT() int64 {
return it.t
}
func (r *sampleRing) at(i int) chunks.Sample {
j := (r.f + i) % len(r.iBuf)
return r.iBuf[j]
}
func (r *sampleRing) atF(i int) fSample {
j := (r.f + i) % len(r.fBuf)
return r.fBuf[j]
}
func (r *sampleRing) atH(i int) hSample {
j := (r.f + i) % len(r.hBuf)
return r.hBuf[j]
}
func (r *sampleRing) atFH(i int) fhSample {
j := (r.f + i) % len(r.fhBuf)
return r.fhBuf[j]
}
// add adds a sample to the ring buffer and frees all samples that fall out of
// the delta range. Note that this method works for any sample
// implementation. If you know you are dealing with one of the implementations
// from this package (fSample, hSample, fhSample), call one of the specialized
// methods addF, addH, or addFH for better performance.
func (r *sampleRing) add(s chunks.Sample) {
if r.bufInUse == noBuf {
// First sample.
switch s := s.(type) {
case fSample:
r.bufInUse = fBuf
r.fBuf = addF(s, r.fBuf, r)
case hSample:
r.bufInUse = hBuf
r.hBuf = addH(s, r.hBuf, r)
case fhSample:
r.bufInUse = fhBuf
r.fhBuf = addFH(s, r.fhBuf, r)
}
return
}
if r.bufInUse != iBuf {
// Nothing added to the interface buf yet. Let's check if we can
// stay specialized.
switch s := s.(type) {
case fSample:
if r.bufInUse == fBuf {
r.fBuf = addF(s, r.fBuf, r)
return
}
case hSample:
if r.bufInUse == hBuf {
r.hBuf = addH(s, r.hBuf, r)
return
}
case fhSample:
if r.bufInUse == fhBuf {
r.fhBuf = addFH(s, r.fhBuf, r)
return
}
}
// The new sample isn't a fit for the already existing
// ones. Copy the latter into the interface buffer where needed.
// The interface buffer is assumed to be of length zero at this point.
switch r.bufInUse {
case fBuf:
for _, s := range r.fBuf {
r.iBuf = append(r.iBuf, s)
}
r.fBuf = nil
case hBuf:
for _, s := range r.hBuf {
r.iBuf = append(r.iBuf, s)
}
r.hBuf = nil
case fhBuf:
for _, s := range r.fhBuf {
r.iBuf = append(r.iBuf, s)
}
r.fhBuf = nil
}
r.bufInUse = iBuf
}
r.iBuf = addSample(s, r.iBuf, r)
}
// addF is a version of the add method specialized for fSample.
func (r *sampleRing) addF(s fSample) {
switch r.bufInUse {
case fBuf: // Add to existing fSamples.
r.fBuf = addF(s, r.fBuf, r)
case noBuf: // Add first sample.
r.fBuf = addF(s, r.fBuf, r)
r.bufInUse = fBuf
case iBuf: // Already have interface samples. Add to the interface buf.
r.iBuf = addSample(s, r.iBuf, r)
default:
// Already have specialized samples that are not fSamples.
// Need to call the checked add method for conversion.
r.add(s)
}
}
// addH is a version of the add method specialized for hSample.
func (r *sampleRing) addH(s hSample) {
switch r.bufInUse {
case hBuf: // Add to existing hSamples.
r.hBuf = addH(s, r.hBuf, r)
case noBuf: // Add first sample.
r.hBuf = addH(s, r.hBuf, r)
r.bufInUse = hBuf
case iBuf: // Already have interface samples. Add to the interface buf.
r.iBuf = addSample(s, r.iBuf, r)
default:
// Already have specialized samples that are not hSamples.
// Need to call the checked add method for conversion.
r.add(s)
}
}
// addFH is a version of the add method specialized for fhSample.
func (r *sampleRing) addFH(s fhSample) {
switch r.bufInUse {
case fhBuf: // Add to existing fhSamples.
r.fhBuf = addFH(s, r.fhBuf, r)
case noBuf: // Add first sample.
r.fhBuf = addFH(s, r.fhBuf, r)
r.bufInUse = fhBuf
case iBuf: // Already have interface samples. Add to the interface buf.
r.iBuf = addSample(s, r.iBuf, r)
default:
// Already have specialized samples that are not fhSamples.
// Need to call the checked add method for conversion.
r.add(s)
}
}
// genericAdd is a generic implementation of adding a chunks.Sample
// implementation to a buffer of a sample ring. However, the Go compiler
// currently (go1.20) decides to not expand the code during compile time, but
// creates dynamic code to handle the different types. That has a significant
// overhead during runtime, noticeable in PromQL benchmarks. For example, the
// "RangeQuery/expr=rate(a_hundred[1d]),steps=.*" benchmarks show about 7%
// longer runtime, 9% higher allocation size, and 10% more allocations.
// Therefore, genericAdd has been manually implemented for all the types
// (addSample, addF, addH, addFH) below.
//
// func genericAdd[T chunks.Sample](s T, buf []T, r *sampleRing) []T {
// l := len(buf)
// // Grow the ring buffer if it fits no more elements.
// if l == 0 {
// buf = make([]T, 16)
// l = 16
// }
// if l == r.l {
// newBuf := make([]T, 2*l)
// copy(newBuf[l+r.f:], buf[r.f:])
// copy(newBuf, buf[:r.f])
//
// buf = newBuf
// r.i = r.f
// r.f += l
// l = 2 * l
// } else {
// r.i++
// if r.i >= l {
// r.i -= l
// }
// }
//
// buf[r.i] = s
// r.l++
//
// // Free head of the buffer of samples that just fell out of the range.
// tmin := s.T() - r.delta
// for buf[r.f].T() < tmin {
// r.f++
// if r.f >= l {
// r.f -= l
// }
// r.l--
// }
// return buf
// }
// addSample is a handcoded specialization of genericAdd (see above).
func addSample(s chunks.Sample, buf []chunks.Sample, r *sampleRing) []chunks.Sample {
l := len(buf)
// Grow the ring buffer if it fits no more elements.
if l == 0 {
buf = make([]chunks.Sample, 16)
l = 16
}
if l == r.l {
newBuf := make([]chunks.Sample, 2*l)
copy(newBuf[l+r.f:], buf[r.f:])
copy(newBuf, buf[:r.f])
buf = newBuf
r.i = r.f
r.f += l
l = 2 * l
} else {
r.i++
if r.i >= l {
r.i -= l
}
}
buf[r.i] = s
r.l++
// Free head of the buffer of samples that just fell out of the range.
tmin := s.T() - r.delta
for buf[r.f].T() < tmin {
r.f++
if r.f >= l {
r.f -= l
}
r.l--
}
return buf
}
// addF is a handcoded specialization of genericAdd (see above).
func addF(s fSample, buf []fSample, r *sampleRing) []fSample {
l := len(buf)
// Grow the ring buffer if it fits no more elements.
if l == 0 {
buf = make([]fSample, 16)
l = 16
}
if l == r.l {
newBuf := make([]fSample, 2*l)
copy(newBuf[l+r.f:], buf[r.f:])
copy(newBuf, buf[:r.f])
buf = newBuf
r.i = r.f
r.f += l
l = 2 * l
} else {
r.i++
if r.i >= l {
r.i -= l
}
}
buf[r.i] = s
r.l++
// Free head of the buffer of samples that just fell out of the range.
tmin := s.T() - r.delta
for buf[r.f].T() < tmin {
r.f++
if r.f >= l {
r.f -= l
}
r.l--
}
return buf
}
// addH is a handcoded specialization of genericAdd (see above).
func addH(s hSample, buf []hSample, r *sampleRing) []hSample {
l := len(buf)
// Grow the ring buffer if it fits no more elements.
if l == 0 {
buf = make([]hSample, 16)
l = 16
}
if l == r.l {
newBuf := make([]hSample, 2*l)
copy(newBuf[l+r.f:], buf[r.f:])
copy(newBuf, buf[:r.f])
buf = newBuf
r.i = r.f
r.f += l
l = 2 * l
} else {
r.i++
if r.i >= l {
r.i -= l
}
}
buf[r.i].t = s.t
if buf[r.i].h == nil {
buf[r.i].h = s.h.Copy()
} else {
s.h.CopyTo(buf[r.i].h)
}
r.l++
// Free head of the buffer of samples that just fell out of the range.
tmin := s.T() - r.delta
for buf[r.f].T() < tmin {
r.f++
if r.f >= l {
r.f -= l
}
r.l--
}
return buf
}
// addFH is a handcoded specialization of genericAdd (see above).
func addFH(s fhSample, buf []fhSample, r *sampleRing) []fhSample {
l := len(buf)
// Grow the ring buffer if it fits no more elements.
if l == 0 {
buf = make([]fhSample, 16)
l = 16
}
if l == r.l {
newBuf := make([]fhSample, 2*l)
copy(newBuf[l+r.f:], buf[r.f:])
copy(newBuf, buf[:r.f])
buf = newBuf
r.i = r.f
r.f += l
l = 2 * l
} else {
r.i++
if r.i >= l {
r.i -= l
}
}
buf[r.i].t = s.t
if buf[r.i].fh == nil {
buf[r.i].fh = s.fh.Copy()
} else {
s.fh.CopyTo(buf[r.i].fh)
}
r.l++
// Free head of the buffer of samples that just fell out of the range.
tmin := s.T() - r.delta
for buf[r.f].T() < tmin {
r.f++
if r.f >= l {
r.f -= l
}
r.l--
}
return buf
}
// reduceDelta lowers the buffered time delta, dropping any samples that are
// out of the new delta range.
func (r *sampleRing) reduceDelta(delta int64) bool {
if delta > r.delta {
return false
}
r.delta = delta
if r.l == 0 {
return true
}
switch r.bufInUse {
case fBuf:
genericReduceDelta(r.fBuf, r)
case hBuf:
genericReduceDelta(r.hBuf, r)
case fhBuf:
genericReduceDelta(r.fhBuf, r)
default:
genericReduceDelta(r.iBuf, r)
}
return true
}
func genericReduceDelta[T chunks.Sample](buf []T, r *sampleRing) {
// Free head of the buffer of samples that just fell out of the range.
l := len(buf)
tmin := buf[r.i].T() - r.delta
for buf[r.f].T() < tmin {
r.f++
if r.f >= l {
r.f -= l
}
r.l--
}
}
// nthLast returns the nth most recent element added to the ring.
func (r *sampleRing) nthLast(n int) (chunks.Sample, bool) {
if n > r.l {
return fSample{}, false
}
i := r.l - n
switch r.bufInUse {
case fBuf:
return r.atF(i), true
case hBuf:
return r.atH(i), true
case fhBuf:
return r.atFH(i), true
default:
return r.at(i), true
}
}
func (r *sampleRing) samples() []chunks.Sample {
res := make([]chunks.Sample, r.l)
k := r.f + r.l
var j int
switch r.bufInUse {
case iBuf:
if k > len(r.iBuf) {
k = len(r.iBuf)
j = r.l - k + r.f
}
n := copy(res, r.iBuf[r.f:k])
copy(res[n:], r.iBuf[:j])
case fBuf:
if k > len(r.fBuf) {
k = len(r.fBuf)
j = r.l - k + r.f
}
resF := make([]fSample, r.l)
n := copy(resF, r.fBuf[r.f:k])
copy(resF[n:], r.fBuf[:j])
for i, s := range resF {
res[i] = s
}
case hBuf:
if k > len(r.hBuf) {
k = len(r.hBuf)
j = r.l - k + r.f
}
resH := make([]hSample, r.l)
n := copy(resH, r.hBuf[r.f:k])
copy(resH[n:], r.hBuf[:j])
for i, s := range resH {
res[i] = s
}
case fhBuf:
if k > len(r.fhBuf) {
k = len(r.fhBuf)
j = r.l - k + r.f
}
resFH := make([]fhSample, r.l)
n := copy(resFH, r.fhBuf[r.f:k])
copy(resFH[n:], r.fhBuf[:j])
for i, s := range resFH {
res[i] = s
}
}
return res
}