lib/libm/src/e_coshf.c

   1 /* e_coshf.c -- float version of e_cosh.c.
   2  * Conversion to float by Ian Lance Taylor, Cygnus Support, ian@cygnus.com.
   3  */
   4
   5 /*
   6  * ====================================================
   7  * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
   8  *
   9  * Developed at SunPro, a Sun Microsystems, Inc. business.
  10  * Permission to use, copy, modify, and distribute this
  11  * software is freely granted, provided that this notice
  12  * is preserved.
  13  * ====================================================
  14  *
  15  * $NetBSD: e_coshf.c,v 1.9 2002/05/26 22:01:49 wiz Exp $
  16  * $DragonFly: src/lib/libm/src/e_coshf.c,v 1.1 2005/07/26 21:15:20 joerg Exp $
  17  */
  18
  19 #include <math.h>
  20 #include "math_private.h"
  21
  22 static const float huge = 1.0e30;
  23 static const float one = 1.0, half=0.5;
  24
  25 float
  26 coshf(float x)
  27 {
  28         float t,w;
  29         int32_t ix;
  30
  31         GET_FLOAT_WORD(ix,x);
  32         ix &= 0x7fffffff;
  33
  34     /* x is INF or NaN */
  35         if(ix>=0x7f800000) return x*x;
  36
  37     /* |x| in [0,0.5*ln2], return 1+expm1(|x|)^2/(2*exp(|x|)) */
  38         if(ix<0x3eb17218) {
  39             t = expm1f(fabsf(x));
  40             w = one+t;
  41             if (ix<0x24000000) return w;        /* cosh(tiny) = 1 */
  42             return one+(t*t)/(w+w);
  43         }
  44
  45     /* |x| in [0.5*ln2,22], return (exp(|x|)+1/exp(|x|)/2; */
  46         if (ix < 0x41b00000) {
  47                 t = expf(fabsf(x));
  48                 return half*t+half/t;
  49         }
  50
  51     /* |x| in [22, log(maxdouble)] return half*exp(|x|) */
  52         if (ix < 0x42b17180)  return half*expf(fabsf(x));
  53
  54     /* |x| in [log(maxdouble), overflowthresold] */
  55         if (ix<=0x42b2d4fc) {
  56             w = expf(half*fabsf(x));
  57             t = half*w;
  58             return t*w;
  59         }
  60
  61     /* |x| > overflowthresold, cosh(x) overflow */
  62         return huge*huge;
  63 }