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
  16 #include <sys/cdefs.h>
  17 #if defined(LIBM_SCCS) && !defined(lint)
  18 __RCSID("$NetBSD: e_acoshf.c,v 1.8 2002/05/26 22:01:48 wiz Exp $");
  19 #endif
  20
  21 #include "math.h"
  22 #include "math_private.h"
  23
  24 static const float
  25 one     = 1.0,
  26 ln2     = 6.9314718246e-01;  /* 0x3f317218 */
  27
  28 float
  29 __ieee754_acoshf(float x)
  30 {
  31         float t;
  32         int32_t hx;
  33         GET_FLOAT_WORD(hx,x);
  34         if(hx<0x3f800000) {             /* x < 1 */
  35             return (x-x)/(x-x);
  36         } else if(hx >=0x4d800000) {    /* x > 2**28 */
  37             if(hx >=0x7f800000) {       /* x is inf of NaN */
  38                 return x+x;
  39             } else
  40                 return __ieee754_logf(x)+ln2;   /* acosh(huge)=log(2x) */
  41         } else if (hx==0x3f800000) {
  42             return 0.0;                 /* acosh(1) = 0 */
  43         } else if (hx > 0x40000000) {   /* 2**28 > x > 2 */
  44             t=x*x;
  45             return __ieee754_logf((float)2.0*x-one/(x+__ieee754_sqrtf(t-one)));
  46         } else {                        /* 1<x<2 */
  47             t = x-one;
  48             return log1pf(t+sqrtf((float)2.0*t+t*t));
  49         }
  50 }