You can not select more than 25 topics
Topics must start with a letter or number, can include dashes ('-') and can be up to 35 characters long.
95 lines
2.5 KiB
95 lines
2.5 KiB
/* |
|
Copyright 2015 The Kubernetes 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 resource |
|
|
|
import ( |
|
"math" |
|
"math/big" |
|
"sync" |
|
) |
|
|
|
var ( |
|
// A sync pool to reduce allocation. |
|
intPool sync.Pool |
|
maxInt64 = big.NewInt(math.MaxInt64) |
|
) |
|
|
|
func init() { |
|
intPool.New = func() interface{} { |
|
return &big.Int{} |
|
} |
|
} |
|
|
|
// scaledValue scales given unscaled value from scale to new Scale and returns |
|
// an int64. It ALWAYS rounds up the result when scale down. The final result might |
|
// overflow. |
|
// |
|
// scale, newScale represents the scale of the unscaled decimal. |
|
// The mathematical value of the decimal is unscaled * 10**(-scale). |
|
func scaledValue(unscaled *big.Int, scale, newScale int) int64 { |
|
dif := scale - newScale |
|
if dif == 0 { |
|
return unscaled.Int64() |
|
} |
|
|
|
// Handle scale up |
|
// This is an easy case, we do not need to care about rounding and overflow. |
|
// If any intermediate operation causes overflow, the result will overflow. |
|
if dif < 0 { |
|
return unscaled.Int64() * int64(math.Pow10(-dif)) |
|
} |
|
|
|
// Handle scale down |
|
// We have to be careful about the intermediate operations. |
|
|
|
// fast path when unscaled < max.Int64 and exp(10,dif) < max.Int64 |
|
const log10MaxInt64 = 19 |
|
if unscaled.Cmp(maxInt64) < 0 && dif < log10MaxInt64 { |
|
divide := int64(math.Pow10(dif)) |
|
result := unscaled.Int64() / divide |
|
mod := unscaled.Int64() % divide |
|
if mod != 0 { |
|
return result + 1 |
|
} |
|
return result |
|
} |
|
|
|
// We should only convert back to int64 when getting the result. |
|
divisor := intPool.Get().(*big.Int) |
|
exp := intPool.Get().(*big.Int) |
|
result := intPool.Get().(*big.Int) |
|
defer func() { |
|
intPool.Put(divisor) |
|
intPool.Put(exp) |
|
intPool.Put(result) |
|
}() |
|
|
|
// divisor = 10^(dif) |
|
// TODO: create loop up table if exp costs too much. |
|
divisor.Exp(bigTen, exp.SetInt64(int64(dif)), nil) |
|
// reuse exp |
|
remainder := exp |
|
|
|
// result = unscaled / divisor |
|
// remainder = unscaled % divisor |
|
result.DivMod(unscaled, divisor, remainder) |
|
if remainder.Sign() != 0 { |
|
return result.Int64() + 1 |
|
} |
|
|
|
return result.Int64() |
|
}
|
|
|