mirror of https://github.com/docker/cli.git
96 lines
2.5 KiB
Go
96 lines
2.5 KiB
Go
/*
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Copyright 2015 The Kubernetes Authors.
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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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http://www.apache.org/licenses/LICENSE-2.0
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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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*/
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package resource
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import (
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"math"
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"math/big"
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"sync"
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)
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var (
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// A sync pool to reduce allocation.
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intPool sync.Pool
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maxInt64 = big.NewInt(math.MaxInt64)
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)
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func init() {
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intPool.New = func() interface{} {
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return &big.Int{}
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}
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}
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// scaledValue scales given unscaled value from scale to new Scale and returns
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// an int64. It ALWAYS rounds up the result when scale down. The final result might
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// overflow.
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//
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// scale, newScale represents the scale of the unscaled decimal.
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// The mathematical value of the decimal is unscaled * 10**(-scale).
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func scaledValue(unscaled *big.Int, scale, newScale int) int64 {
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dif := scale - newScale
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if dif == 0 {
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return unscaled.Int64()
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}
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// Handle scale up
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// This is an easy case, we do not need to care about rounding and overflow.
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// If any intermediate operation causes overflow, the result will overflow.
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if dif < 0 {
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return unscaled.Int64() * int64(math.Pow10(-dif))
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}
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// Handle scale down
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// We have to be careful about the intermediate operations.
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// fast path when unscaled < max.Int64 and exp(10,dif) < max.Int64
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const log10MaxInt64 = 19
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if unscaled.Cmp(maxInt64) < 0 && dif < log10MaxInt64 {
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divide := int64(math.Pow10(dif))
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result := unscaled.Int64() / divide
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mod := unscaled.Int64() % divide
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if mod != 0 {
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return result + 1
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}
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return result
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}
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// We should only convert back to int64 when getting the result.
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divisor := intPool.Get().(*big.Int)
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exp := intPool.Get().(*big.Int)
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result := intPool.Get().(*big.Int)
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defer func() {
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intPool.Put(divisor)
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intPool.Put(exp)
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intPool.Put(result)
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}()
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// divisor = 10^(dif)
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// TODO: create loop up table if exp costs too much.
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divisor.Exp(bigTen, exp.SetInt64(int64(dif)), nil)
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// reuse exp
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remainder := exp
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// result = unscaled / divisor
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// remainder = unscaled % divisor
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result.DivMod(unscaled, divisor, remainder)
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if remainder.Sign() != 0 {
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return result.Int64() + 1
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}
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return result.Int64()
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}
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