text: 
  /* @(#)e_cosh.c 1.3 95/01/18 */
  /* $FreeBSD: head/lib/msun/src/e_cosh.c 226598 2011-10-21 06:28:47Z das $ */
  /*
   * ====================================================
   * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
   *
   * Developed at SunSoft, a Sun Microsystems, Inc. business.
   * Permission to use, copy, modify, and distribute this
   * software is freely granted, provided that this notice 
   * is preserved.
   * ====================================================
   */
  
  /* __ieee754_cosh(x)
   * Method : 
   * mathematically cosh(x) if defined to be (exp(x)+exp(-x))/2
   *	1. Replace x by |x| (cosh(x) = cosh(-x)). 
   *	2. 
   *		                                        [ exp(x) - 1 ]^2 
   *	    0        <= x <= ln2/2  :  cosh(x) := 1 + -------------------
   *			       			           2*exp(x)
   *
   *		                                  exp(x) +  1/exp(x)
   *	    ln2/2    <= x <= 22     :  cosh(x) := -------------------
   *			       			          2
   *	    22       <= x <= lnovft :  cosh(x) := exp(x)/2 
   *	    lnovft   <= x <= ln2ovft:  cosh(x) := exp(x/2)/2 * exp(x/2)
   *	    ln2ovft  <  x	    :  cosh(x) := huge*huge (overflow)
   *
   * Special cases:
   *	cosh(x) is |x| if x is +INF, -INF, or NaN.
   *	only cosh(0)=1 is exact for finite x.
   */
  
  #include "math.h"
  #include "math_private.h"
  
  static const double one = 1.0, half=0.5, huge = 1.0e300;
  
  double
  __ieee754_cosh(double x)
  {
  	double t,w;
  	int32_t ix;
  
      /* High word of |x|. */
  	GET_HIGH_WORD(ix,x);
  	ix &= 0x7fffffff;
  
      /* x is INF or NaN */
  	if(ix>=0x7ff00000) return x*x;	
  
      /* |x| in [0,0.5*ln2], return 1+expm1(|x|)^2/(2*exp(|x|)) */
  	if(ix<0x3fd62e43) {
  	    t = expm1(fabs(x));
  	    w = one+t;
  	    if (ix<0x3c800000) return w;	/* cosh(tiny) = 1 */
  	    return one+(t*t)/(w+w);
  	}
  
      /* |x| in [0.5*ln2,22], return (exp(|x|)+1/exp(|x|)/2; */
  	if (ix < 0x40360000) {
  		t = __ieee754_exp(fabs(x));
  		return half*t+half/t;
  	}
  
      /* |x| in [22, log(maxdouble)] return half*exp(|x|) */
  	if (ix < 0x40862E42)  return half*__ieee754_exp(fabs(x));
  
      /* |x| in [log(maxdouble), overflowthresold] */
  	if (ix<=0x408633CE)
  	    return __ldexp_exp(fabs(x), -1);
  
      /* |x| > overflowthresold, cosh(x) overflow */
  	return huge*huge;
  }
  