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  1. /* Copyright (C) 1994 DJ Delorie, see COPYING.DJ for details */
  2. /* e_coshf.c -- float version of e_cosh.c.
  3.  * Conversion to float by Ian Lance Taylor, Cygnus Support, ian@cygnus.com.
  4.  */
  5.  
  6. /*
  7.  * ====================================================
  8.  * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
  9.  *
  10.  * Developed at SunPro, a Sun Microsystems, Inc. business.
  11.  * Permission to use, copy, modify, and distribute this
  12.  * software is freely granted, provided that this notice
  13.  * is preserved.
  14.  * ====================================================
  15.  */
  16.  
  17. #if defined(LIBM_SCCS) && !defined(lint)
  18. static char rcsid[] = "$Id: e_coshf.c,v 1.2 1994/08/18 23:05:17 jtc Exp $";
  19. #endif
  20.  
  21. #include "math.h"
  22. #include "math_private.h"
  23.  
  24. #ifdef __STDC__
  25. static const float one = 1.0, half=0.5, huge = 1.0e30;
  26. #else
  27. static float one = 1.0, half=0.5, huge = 1.0e30;
  28. #endif
  29.  
  30. #ifdef __STDC__
  31.         float __ieee754_coshf(float x)
  32. #else
  33.         float __ieee754_coshf(x)
  34.         float x;
  35. #endif
  36. {      
  37.         float t,w;
  38.         int32_t ix;
  39.  
  40.         GET_FLOAT_WORD(ix,x);
  41.         ix &= 0x7fffffff;
  42.  
  43.     /* x is INF or NaN */
  44.         if(ix>=0x7f800000) return x*x; 
  45.  
  46.     /* |x| in [0,0.5*ln2], return 1+expm1(|x|)^2/(2*exp(|x|)) */
  47.         if(ix<0x3eb17218) {
  48.             t = expm1f(fabsf(x));
  49.             w = one+t;
  50.             if (ix<0x24000000) return w;        /* cosh(tiny) = 1 */
  51.             return one+(t*t)/(w+w);
  52.         }
  53.  
  54.     /* |x| in [0.5*ln2,22], return (exp(|x|)+1/exp(|x|)/2; */
  55.         if (ix < 0x41b00000) {
  56.                 t = __ieee754_expf(fabsf(x));
  57.                 return half*t+half/t;
  58.         }
  59.  
  60.     /* |x| in [22, log(maxdouble)] return half*exp(|x|) */
  61.         if (ix < 0x42b17180)  return half*__ieee754_expf(fabsf(x));
  62.  
  63.     /* |x| in [log(maxdouble), overflowthresold] */
  64.         if (ix<=0x42b2d4fc) {
  65.             w = __ieee754_expf(half*fabsf(x));
  66.             t = half*w;
  67.             return t*w;
  68.         }
  69.  
  70.     /* |x| > overflowthresold, cosh(x) overflow */
  71.         return huge*huge;
  72. }
  73.