mirror of
https://github.com/TwiN/gatus.git
synced 2024-12-03 05:14:52 +01:00
96 lines
2.5 KiB
Go
96 lines
2.5 KiB
Go
/*
|
|
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()
|
|
}
|