50 lines
1.3 KiB
Go
50 lines
1.3 KiB
Go
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/*
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Copyright (c) 2012, Jan Schlicht <jan.schlicht@gmail.com>
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Permission to use, copy, modify, and/or distribute this software for any purpose
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with or without fee is hereby granted, provided that the above copyright notice
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and this permission notice appear in all copies.
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THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES WITH
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REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY AND
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FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY SPECIAL, DIRECT,
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INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS
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OF USE, DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER
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TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR PERFORMANCE OF
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THIS SOFTWARE.
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*/
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package resize
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import (
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"math"
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)
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var (
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epsilon = math.Nextafter(1.0, 2.0) - 1.0 // machine epsilon
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taylor2bound = math.Sqrt(epsilon)
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taylorNbound = math.Sqrt(taylor2bound)
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)
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// unnormalized sinc function
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func Sinc1(x float64) (y float64) {
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if math.Abs(x) >= taylorNbound {
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y = math.Sin(x) / x
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} else {
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y = 1.0
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if math.Abs(x) >= epsilon {
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x2 := x * x
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y -= x2 / 6.0
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if math.Abs(x) >= taylor2bound {
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y += (x2 * x2) / 120.0
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}
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}
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}
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return
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}
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// normalized sinc function
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func Sinc(x float64) float64 {
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return Sinc1(x * math.Pi)
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}
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