/*
Copyright 2023 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 sdkmath

import "math"

// Copy from https://github.com/aws/aws-sdk-go
// May have been modified by Beijing Volcanoengine Technology Ltd.

// Copied from the Go standard library's (Go 1.12) math/floor.go for use in
// Go version prior to Go 1.10.
const (
	uvone    = 0x3FF0000000000000
	mask     = 0x7FF
	shift    = 64 - 11 - 1
	bias     = 1023
	signMask = 1 << 63
	fracMask = 1<<shift - 1
)

// Round returns the nearest integer, rounding half away from zero.
//
// Special cases are:
//
//	Round(±0) = ±0
//	Round(±Inf) = ±Inf
//	Round(NaN) = NaN
//
// Copied from the Go standard library's (Go 1.12) math/floor.go for use in
// Go version prior to Go 1.10.
func Round(x float64) float64 {
	// Round is a faster implementation of:
	//
	// func Round(x float64) float64 {
	//   t := Trunc(x)
	//   if Abs(x-t) >= 0.5 {
	//     return t + Copysign(1, x)
	//   }
	//   return t
	// }
	bits := math.Float64bits(x)
	e := uint(bits>>shift) & mask
	if e < bias {
		// Round abs(x) < 1 including denormals.
		bits &= signMask // +-0
		if e == bias-1 {
			bits |= uvone // +-1
		}
	} else if e < bias+shift {
		// Round any abs(x) >= 1 containing a fractional component [0,1).
		//
		// Numbers with larger exponents are returned unchanged since they
		// must be either an integer, infinity, or NaN.
		const half = 1 << (shift - 1)
		e -= bias
		bits += half >> e
		bits &^= fracMask >> e
	}
	return math.Float64frombits(bits)
}