newlib/libm/mathfp/ef_acosh.c

   1 /* ef_acosh.c -- float version of e_acosh.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
  17 #include "fdlibm.h"
  18
  19 #ifdef __STDC__
  20 static const float
  21 #else
  22 static float
  23 #endif
  24 one     = 1.0,
  25 ln2     = 6.9314718246e-01;  /* 0x3f317218 */
  26
  27 #ifdef __STDC__
  28         float acoshf(float x)
  29 #else
  30         float acoshf(x)
  31         float x;
  32 #endif
  33 {
  34         float t;
  35         __int32_t hx;
  36         GET_FLOAT_WORD(hx,x);
  37         if(hx<0x3f800000) {             /* x < 1 */
  38             return (x-x)/(x-x);
  39         } else if(hx >=0x4d800000) {    /* x > 2**28 */
  40             if(hx >=0x7f800000) {       /* x is inf of NaN */
  41                 return x+x;
  42             } else
  43                 return logf(x)+ln2;     /* acosh(huge)=log(2x) */
  44         } else if (hx==0x3f800000) {
  45             return 0.0;                 /* acosh(1) = 0 */
  46         } else if (hx > 0x40000000) {   /* 2**28 > x > 2 */
  47             t=x*x;
  48             return logf((float)2.0*x-one/(x+sqrtf(t-one)));
  49         } else {                        /* 1<x<2 */
  50             t = x-one;
  51             return log1pf(t+sqrtf((float)2.0*t+t*t));
  52         }
  53 }