POK
e_coshf.c
1 /*
2  * POK header
3  *
4  * The following file is a part of the POK project. Any modification should
5  * made according to the POK licence. You CANNOT use this file or a part of
6  * this file is this part of a file for your own project
7  *
8  * For more information on the POK licence, please see our LICENCE FILE
9  *
10  * Please follow the coding guidelines described in doc/CODING_GUIDELINES
11  *
12  * Copyright (c) 2007-2009 POK team
13  *
14  * Created by julien on Fri Jan 30 14:41:34 2009
15  */
16 
17 /* e_coshf.c -- float version of e_cosh.c.
18  * Conversion to float by Ian Lance Taylor, Cygnus Support, ian@cygnus.com.
19  */
20 
21 /*
22  * ====================================================
23  * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
24  *
25  * Developed at SunPro, a Sun Microsystems, Inc. business.
26  * Permission to use, copy, modify, and distribute this
27  * software is freely granted, provided that this notice
28  * is preserved.
29  * ====================================================
30  */
31 
32 #ifdef POK_NEEDS_LIBMATH
33 #include <libm.h>
34 #include "math_private.h"
35 
36 static const float huge = 1.0e30;
37 static const float one = 1.0, half=0.5;
38 
39 float
40 __ieee754_coshf(float x)
41 {
42  float t,w;
43  int32_t ix;
44 
45  GET_FLOAT_WORD(ix,x);
46  ix &= 0x7fffffff;
47 
48  /* x is INF or NaN */
49  if(ix>=0x7f800000) return x*x;
50 
51  /* |x| in [0,0.5*ln2], return 1+expm1(|x|)^2/(2*exp(|x|)) */
52  if(ix<0x3eb17218) {
53  t = expm1f(fabsf(x));
54  w = one+t;
55  if (ix<0x24000000) return w; /* cosh(tiny) = 1 */
56  return one+(t*t)/(w+w);
57  }
58 
59  /* |x| in [0.5*ln2,22], return (exp(|x|)+1/exp(|x|)/2; */
60  if (ix < 0x41b00000) {
61  t = __ieee754_expf(fabsf(x));
62  return half*t+half/t;
63  }
64 
65  /* |x| in [22, log(maxdouble)] return half*exp(|x|) */
66  if (ix < 0x42b17180) return half*__ieee754_expf(fabsf(x));
67 
68  /* |x| in [log(maxdouble), overflowthresold] */
69  if (ix<=0x42b2d4fc) {
70  w = __ieee754_expf(half*fabsf(x));
71  t = half*w;
72  return t*w;
73  }
74 
75  /* |x| > overflowthresold, cosh(x) overflow */
76  return huge*huge;
77 }
78 #endif
79