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-rw-r--r--src/math/sinh.go93
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diff --git a/src/math/sinh.go b/src/math/sinh.go
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+// 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.
+
+package math
+
+/*
+ Floating-point hyperbolic sine and cosine.
+
+ The exponential func is called for arguments
+ greater in magnitude than 0.5.
+
+ A series is used for arguments smaller in magnitude than 0.5.
+
+ Cosh(x) is computed from the exponential func for
+ all arguments.
+*/
+
+// Sinh returns the hyperbolic sine of x.
+//
+// Special cases are:
+//
+// Sinh(±0) = ±0
+// Sinh(±Inf) = ±Inf
+// Sinh(NaN) = NaN
+func Sinh(x float64) float64 {
+ if haveArchSinh {
+ return archSinh(x)
+ }
+ return sinh(x)
+}
+
+func sinh(x float64) float64 {
+ // The coefficients are #2029 from Hart & Cheney. (20.36D)
+ const (
+ P0 = -0.6307673640497716991184787251e+6
+ P1 = -0.8991272022039509355398013511e+5
+ P2 = -0.2894211355989563807284660366e+4
+ P3 = -0.2630563213397497062819489e+2
+ Q0 = -0.6307673640497716991212077277e+6
+ Q1 = 0.1521517378790019070696485176e+5
+ Q2 = -0.173678953558233699533450911e+3
+ )
+
+ sign := false
+ if x < 0 {
+ x = -x
+ sign = true
+ }
+
+ var temp float64
+ switch {
+ case x > 21:
+ temp = Exp(x) * 0.5
+
+ case x > 0.5:
+ ex := Exp(x)
+ temp = (ex - 1/ex) * 0.5
+
+ default:
+ sq := x * x
+ temp = (((P3*sq+P2)*sq+P1)*sq + P0) * x
+ temp = temp / (((sq+Q2)*sq+Q1)*sq + Q0)
+ }
+
+ if sign {
+ temp = -temp
+ }
+ return temp
+}
+
+// Cosh returns the hyperbolic cosine of x.
+//
+// Special cases are:
+//
+// Cosh(±0) = 1
+// Cosh(±Inf) = +Inf
+// Cosh(NaN) = NaN
+func Cosh(x float64) float64 {
+ if haveArchCosh {
+ return archCosh(x)
+ }
+ return cosh(x)
+}
+
+func cosh(x float64) float64 {
+ x = Abs(x)
+ if x > 21 {
+ return Exp(x) * 0.5
+ }
+ ex := Exp(x)
+ return (ex + 1/ex) * 0.5
+}