ref: 1415efdcd838cf482072ef08e765a8ce960bfdde
dir: /tpl/math/round.go/
// Copyright 2009 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
// According to https://github.com/golang/go/issues/20100, the Go stdlib will
// include math.Round beginning with Go 1.10.
//
// The following implementation was taken from https://golang.org/cl/43652.
package math
import "math"
const (
mask = 0x7FF
shift = 64 - 11 - 1
bias = 1023
)
// Round returns the nearest integer, rounding half away from zero.
//
// Special cases are:
// Round(±0) = ±0
// Round(±Inf) = ±Inf
// Round(NaN) = NaN
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
// }
const (
signMask = 1 << 63
fracMask = 1<<shift - 1
half = 1 << (shift - 1)
one = bias << shift
)
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 |= one // +-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.
e -= bias
bits += half >> e
bits &^= fracMask >> e
}
return math.Float64frombits(bits)
}