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63 lines
1.4 KiB
Go
63 lines
1.4 KiB
Go
// Copyright 2009 The Go Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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// According to https://github.com/golang/go/issues/20100, the Go stdlib will
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// include math.Round beginning with Go 1.10.
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//
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// The following implementation was taken from https://golang.org/cl/43652.
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package math
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import "math"
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const (
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mask = 0x7FF
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shift = 64 - 11 - 1
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bias = 1023
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)
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// Round returns the nearest integer, rounding half away from zero.
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//
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// Special cases are:
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//
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// Round(±0) = ±0
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// Round(±Inf) = ±Inf
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// Round(NaN) = NaN
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func _round(x float64) float64 {
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// Round is a faster implementation of:
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//
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// func Round(x float64) float64 {
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// t := Trunc(x)
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// if Abs(x-t) >= 0.5 {
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// return t + Copysign(1, x)
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// }
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// return t
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// }
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const (
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signMask = 1 << 63
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fracMask = 1<<shift - 1
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half = 1 << (shift - 1)
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one = bias << shift
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)
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bits := math.Float64bits(x)
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e := uint(bits>>shift) & mask
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if e < bias {
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// Round abs(x) < 1 including denormals.
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bits &= signMask // +-0
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if e == bias-1 {
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bits |= one // +-1
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}
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} else if e < bias+shift {
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// Round any abs(x) >= 1 containing a fractional component [0,1).
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//
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// Numbers with larger exponents are returned unchanged since they
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// must be either an integer, infinity, or NaN.
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e -= bias
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bits += half >> e
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bits &^= fracMask >> e
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}
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return math.Float64frombits(bits)
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}
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