POK
e_acoshf.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_acoshf.c -- float version of e_acosh.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 
34 #include <libm.h>
35 #include "math_private.h"
36 
37 static const float
38 one = 1.0,
39 ln2 = 6.9314718246e-01; /* 0x3f317218 */
40 
41 float
42 __ieee754_acoshf(float x)
43 {
44  float t;
45  int32_t hx;
46  GET_FLOAT_WORD(hx,x);
47  if(hx<0x3f800000) { /* x < 1 */
48  return (x-x)/(x-x);
49  } else if(hx >=0x4d800000) { /* x > 2**28 */
50  if(hx >=0x7f800000) { /* x is inf of NaN */
51  return x+x;
52  } else
53  return __ieee754_logf(x)+ln2; /* acosh(huge)=log(2x) */
54  } else if (hx==0x3f800000) {
55  return 0.0; /* acosh(1) = 0 */
56  } else if (hx > 0x40000000) { /* 2**28 > x > 2 */
57  t=x*x;
58  return __ieee754_logf((float)2.0*x-one/(x+__ieee754_sqrtf(t-one)));
59  } else { /* 1<x<2 */
60  t = x-one;
61  return log1pf(t+sqrtf((float)2.0*t+t*t));
62  }
63 }
64 
65 #endif
66