mirror of
https://github.com/netbirdio/gvisor.git
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Etienne Perot
cb0481301f
This adds a new atomic type, `atomicbitops.Float64`, which has similar operations as `atomicbitops.Uint64`. It actually uses `atomicbitops.Uint64` for storing its bits. `atomicbitops.Float64` supports `Swap`, `CompareAndSwap`, and `Add` operations. This is useful in gVisor's metric library for keeping track of the sum-of-squared-deviation statistic of distribution metrics. PiperOrigin-RevId: 537127647
106 lines
3.0 KiB
Go
106 lines
3.0 KiB
Go
// Copyright 2023 The gVisor Authors.
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//
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// Licensed under the Apache License, Version 2.0 (the "License");
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// you may not use this file except in compliance with the License.
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// You may obtain a copy of the License at
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//
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// http://www.apache.org/licenses/LICENSE-2.0
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//
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// Unless required by applicable law or agreed to in writing, software
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// distributed under the License is distributed on an "AS IS" BASIS,
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// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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// See the License for the specific language governing permissions and
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// limitations under the License.
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package atomicbitops
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import (
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"math"
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"gvisor.dev/gvisor/pkg/sync"
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)
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// Float64 is an atomic 64-bit floating-point number.
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//
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// +stateify savable
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type Float64 struct {
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_ sync.NoCopy
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// bits stores the bit of a 64-bit floating point number.
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// It is not (and should not be interpreted as) a real uint64.
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bits Uint64
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}
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// FromFloat64 returns a Float64 initialized to value v.
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//
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//go:nosplit
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func FromFloat64(v float64) Float64 {
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return Float64{bits: FromUint64(math.Float64bits(v))}
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}
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// Load loads the floating-point value.
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//
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//go:nosplit
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func (f *Float64) Load() float64 {
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return math.Float64frombits(f.bits.Load())
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}
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// RacyLoad is analogous to reading an atomic value without using
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// synchronization.
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//
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// It may be helpful to document why a racy operation is permitted.
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//
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//go:nosplit
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func (f *Float64) RacyLoad() float64 {
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return math.Float64frombits(f.bits.RacyLoad())
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}
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// Store stores the given floating-point value in the Float64.
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//
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//go:nosplit
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func (f *Float64) Store(v float64) {
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f.bits.Store(math.Float64bits(v))
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}
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// RacyStore is analogous to setting an atomic value without using
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// synchronization.
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//
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// It may be helpful to document why a racy operation is permitted.
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//
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//go:nosplit
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func (f *Float64) RacyStore(v float64) {
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f.bits.RacyStore(math.Float64bits(v))
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}
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// Swap stores the given value and returns the previously-stored one.
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//
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//go:nosplit
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func (f *Float64) Swap(v float64) float64 {
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return math.Float64frombits(f.bits.Swap(math.Float64bits(v)))
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}
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// CompareAndSwap does a compare-and-swap operation on the float64 value.
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// Note that unlike typical IEEE 754 semantics, this function will treat NaN
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// as equal to itself if all of its bits exactly match.
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//
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//go:nosplit
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func (f *Float64) CompareAndSwap(oldVal, newVal float64) bool {
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return f.bits.CompareAndSwap(math.Float64bits(oldVal), math.Float64bits(newVal))
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}
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// Add increments the float by the given value.
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// Note that unlike an atomic integer, this requires spin-looping until we win
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// the compare-and-swap race, so this may take an indeterminate amount of time.
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//
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//go:nosplit
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func (f *Float64) Add(v float64) {
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// We do a racy load here because we optimistically think it may pass the
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// compare-and-swap operation. If it doesn't, we'll load it safely, so this
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// is OK and not a race for the overall intent of the user to add a number.
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sync.RaceDisable()
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oldVal := f.RacyLoad()
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for !f.CompareAndSwap(oldVal, oldVal+v) {
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oldVal = f.Load()
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}
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sync.RaceEnable()
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}
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