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  1. /* Copyright (C) 1994 DJ Delorie, see COPYING.DJ for details */
  2. /* e_acoshf.c -- float version of e_acosh.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_acoshf.c,v 1.2 1994/08/18 23:04:57 jtc Exp $";
  19. #endif
  20.  
  21. #include "math.h"
  22. #include "math_private.h"
  23.  
  24. #ifdef __STDC__
  25. static const float
  26. #else
  27. static float
  28. #endif
  29. one     = 1.0,
  30. ln2     = 6.9314718246e-01;  /* 0x3f317218 */
  31.  
  32. #ifdef __STDC__
  33.         float __ieee754_acoshf(float x)
  34. #else
  35.         float __ieee754_acoshf(x)
  36.         float x;
  37. #endif
  38. {      
  39.         float t;
  40.         int32_t hx;
  41.         GET_FLOAT_WORD(hx,x);
  42.         if(hx<0x3f800000) {             /* x < 1 */
  43.             return (x-x)/(x-x);
  44.         } else if(hx >=0x4d800000) {    /* x > 2**28 */
  45.             if(hx >=0x7f800000) {       /* x is inf of NaN */
  46.                 return x+x;
  47.             } else
  48.                 return __ieee754_logf(x)+ln2;   /* acosh(huge)=log(2x) */
  49.         } else if (hx==0x3f800000) {
  50.             return 0.0;                 /* acosh(1) = 0 */
  51.         } else if (hx > 0x40000000) {   /* 2**28 > x > 2 */
  52.             t=x*x;
  53.             return __ieee754_logf((float)2.0*x-one/(x+sqrtf(t-one)));
  54.         } else {                        /* 1<x<2 */
  55.             t = x-one;
  56.             return log1pf(t+sqrtf((float)2.0*t+t*t));
  57.         }
  58. }
  59.