1
// Copyright 2010 The Go Authors. All rights reserved.
2
// Use of this source code is governed by a BSD-style
3
// license that can be found in the LICENSE file.
8
// The original C code, the long comment, and the constants
9
// below are from FreeBSD's /usr/src/lib/msun/src/e_acosh.c
10
// and came with this notice. The go code is a simplified
11
// version of the original C.
13
// ====================================================
14
// Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
16
// Developed at SunPro, a Sun Microsystems, Inc. business.
17
// Permission to use, copy, modify, and distribute this
18
// software is freely granted, provided that this notice
20
// ====================================================
26
// acosh(x) = log [ x + sqrt(x*x-1) ]
28
// acosh(x) := log(x)+ln2, if x is large; else
29
// acosh(x) := log(2x-1/(sqrt(x*x-1)+x)) if x>2; else
30
// acosh(x) := log1p(t+sqrt(2.0*t+t*t)); where t=x-1.
33
// acosh(x) is NaN with signal if x<1.
34
// acosh(NaN) is NaN without signal.
37
// Acosh(x) calculates the inverse hyperbolic cosine of x.
40
// Acosh(x) = NaN if x < 1
42
func Acosh(x float64) float64 {
44
Ln2 = 6.93147180559945286227e-01 // 0x3FE62E42FEFA39EF
45
Large = 1 << 28 // 2**28
47
// TODO(rsc): Remove manual inlining of IsNaN
48
// when compiler does it for us
49
// first case is special case
51
case x < 1 || x != x: // x < 1 || IsNaN(x):
56
return Log(x) + Ln2 // x > 2**28
58
return Log(2*x - 1/(x+Sqrt(x*x-1))) // 2**28 > x > 2
61
return Log1p(t + Sqrt(2*t+t*t)) // 2 >= x > 1