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https://github.com/make-42/xyosc
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78 lines
1.5 KiB
Go
78 lines
1.5 KiB
Go
package math32
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// The original C code, the long comment, and the constants
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// below were from http://netlib.sandia.gov/cephes/cmath/tanh.c,
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// available from http://www.netlib.org/cephes/single.tgz.
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// The go code is a simplified version of the original C.
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// tanhf.c
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//
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// Hyperbolic tangent
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//
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//
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//
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// SYNOPSIS:
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//
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// float x, y, tanhf();
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//
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// y = tanhf( x );
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//
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//
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//
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// DESCRIPTION:
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//
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// Returns hyperbolic tangent of argument in the range MINLOG to
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// MAXLOG.
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//
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// A polynomial approximation is used for |x| < 0.625.
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// Otherwise,
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//
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// tanh(x) = sinh(x)/cosh(x) = 1 - 2/(exp(2x) + 1).
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//
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//
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//
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// ACCURACY:
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//
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// Relative error:
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// arithmetic domain # trials peak rms
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// IEEE -2,2 100000 1.3e-7 2.6e-8
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//
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//
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/*
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Cephes Math Library Release 2.2: June, 1992
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Copyright 1984, 1987, 1989, 1992 by Stephen L. Moshier
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Direct inquiries to 30 Frost Street, Cambridge, MA 02140
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*/
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/* Single precision hyperbolic tangent
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* test interval: [-0.625, +0.625]
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* trials: 10000
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* peak relative error: 7.2e-8
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* rms relative error: 2.6e-8
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*/
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func Tanh(x float32) float32 {
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const MAXLOG = 88.02969187150841
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z := Abs(x)
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switch {
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case z > 0.5*MAXLOG:
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if x < 0 {
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return -1
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}
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return 1
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case z >= 0.625:
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s := Exp(z + z)
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z = 1 - 2/(s+1)
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if x < 0 {
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z = -z
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}
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default:
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if x == 0 {
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return x
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}
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s := x * x
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z = ((((-5.70498872745E-3*s+2.06390887954E-2)*s-5.37397155531E-2)*s+1.33314422036E-1)*s-3.33332819422E-1)*s*x + x
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}
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return z
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}
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