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@gdm85 gdm85/round.go
Created Nov 22, 2017

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Round function for Go < 1.10
package main
import (
"math"
)
// some constants copied from https://github.com/golang/go/blob/master/src/math/bits.go
const (
shift = 64 - 11 - 1
bias = 1023
mask = 0x7FF
)
// Round returns the nearest integer, rounding half away from zero.
// This function is available natively in Go 1.10
//
// 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)
}
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