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
  16 #include <sys/cdefs.h>
  17 #if defined(LIBM_SCCS) && !defined(lint)
  18 __RCSID("$NetBSD: e_coshf.c,v 1.8 1999/07/02 15:37:38 simonb Exp $");
  19 #endif
  20
  21 #include "math.h"
  22 #include "math_private.h"
  23
  24 static const float huge = 1.0e30;
  25 static const float one = 1.0, half=0.5;
  26
  27 float
  28 __ieee754_coshf(float x)
  29 {
  30         float t,w;
  31         int32_t ix;
  32
  33         GET_FLOAT_WORD(ix,x);
  34         ix &= 0x7fffffff;
  35
  36     /* x is INF or NaN */
  37         if(ix>=0x7f800000) return x*x;
  38
  39     /* |x| in [0,0.5*ln2], return 1+expm1(|x|)^2/(2*exp(|x|)) */
  40         if(ix<0x3eb17218) {
  41             t = expm1f(fabsf(x));
  42             w = one+t;
  43             if (ix<0x24000000) return w;        /* cosh(tiny) = 1 */
  44             return one+(t*t)/(w+w);
  45         }
  46
  47     /* |x| in [0.5*ln2,22], return (exp(|x|)+1/exp(|x|)/2; */
  48         if (ix < 0x41b00000) {
  49                 t = __ieee754_expf(fabsf(x));
  50                 return half*t+half/t;
  51         }
  52
  53     /* |x| in [22, log(maxdouble)] return half*exp(|x|) */
  54         if (ix < 0x42b17180)  return half*__ieee754_expf(fabsf(x));
  55
  56     /* |x| in [log(maxdouble), overflowthresold] */
  57         if (ix<=0x42b2d4fc) {
  58             w = __ieee754_expf(half*fabsf(x));
  59             t = half*w;
  60             return t*w;
  61         }
  62
  63     /* |x| > overflowthresold, cosh(x) overflow */
  64         return huge*huge;
  65 }