lib/libm/src/e_acoshf.c

   1 /* e_acoshf.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  * $NetBSD: e_acoshf.c,v 1.8 2002/05/26 22:01:48 wiz Exp $
  16  * $DragonFly: src/lib/libm/src/e_acoshf.c,v 1.1 2005/07/26 21:15:20 joerg Exp $
  17  */
  18
  19 #include <math.h>
  20 #include "math_private.h"
  21
  22 static const float
  23 one     = 1.0,
  24 ln2     = 6.9314718246e-01;  /* 0x3f317218 */
  25
  26 float
  27 acoshf(float x)
  28 {
  29         float t;
  30         int32_t hx;
  31         GET_FLOAT_WORD(hx,x);
  32         if(hx<0x3f800000) {             /* x < 1 */
  33             return (x-x)/(x-x);
  34         } else if(hx >=0x4d800000) {    /* x > 2**28 */
  35             if(hx >=0x7f800000) {       /* x is inf of NaN */
  36                 return x+x;
  37             } else
  38                 return logf(x)+ln2;     /* acosh(huge)=log(2x) */
  39         } else if (hx==0x3f800000) {
  40             return 0.0;                 /* acosh(1) = 0 */
  41         } else if (hx > 0x40000000) {   /* 2**28 > x > 2 */
  42             t=x*x;
  43             return logf((float)2.0*x-one/(x+sqrtf(t-one)));
  44         } else {                        /* 1<x<2 */
  45             t = x-one;
  46             return log1pf(t+sqrtf((float)2.0*t+t*t));
  47         }
  48 }