sysdeps/ieee754/ldbl-128/s_tanhl.c

   1 /* s_tanhl.c -- long double version of s_tanh.c.
   2  * Conversion to long double by Ulrich Drepper,
   3  * Cygnus Support, drepper@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 /* Changes for 128-bit long double contributed by
  18    Stephen L. Moshier <moshier@na-net.ornl.gov> */
  19
  20 /* tanhl(x)
  21  * Return the Hyperbolic Tangent of x
  22  *
  23  * Method :
  24  *                                      x    -x
  25  *                                     e  - e
  26  *      0. tanhl(x) is defined to be -----------
  27  *                                      x    -x
  28  *                                     e  + e
  29  *      1. reduce x to non-negative by tanhl(-x) = -tanhl(x).
  30  *      2.  0      <= x <= 2**-57 : tanhl(x) := x*(one+x)
  31  *                                               -t
  32  *          2**-57 <  x <=  1     : tanhl(x) := -----; t = expm1l(-2x)
  33  *                                              t + 2
  34  *                                                    2
  35  *          1      <= x <=  40.0  : tanhl(x) := 1-  ----- ; t=expm1l(2x)
  36  *                                                  t + 2
  37  *          40.0   <  x <= INF    : tanhl(x) := 1.
  38  *
  39  * Special cases:
  40  *      tanhl(NaN) is NaN;
  41  *      only tanhl(0)=0 is exact for finite argument.
  42  */
  43
  44 #include "math.h"
  45 #include "math_private.h"
  46
  47 #ifdef __STDC__
  48 static const long double one = 1.0, two = 2.0, tiny = 1.0e-4900L;
  49 #else
  50 static long double one = 1.0, two = 2.0, tiny = 1.0e-4900L;
  51 #endif
  52
  53 #ifdef __STDC__
  54 long double
  55 __tanhl (long double x)
  56 #else
  57 long double
  58 __tanhl (x)
  59      long double x;
  60 #endif
  61 {
  62   long double t, z;
  63   u_int32_t jx, ix;
  64   ieee854_long_double_shape_type u;
  65
  66   /* Words of |x|. */
  67   u.value = x;
  68   jx = u.parts32.w0;
  69   ix = jx & 0x7fffffff;
  70   /* x is INF or NaN */
  71   if (ix >= 0x7fff0000)
  72     {
  73       /* for NaN it's not important which branch: tanhl(NaN) = NaN */
  74       if (jx & 0x80000000)
  75         return one / x - one;   /* tanhl(-inf)= -1; */
  76       else
  77         return one / x + one;   /* tanhl(+inf)=+1 */
  78     }
  79
  80   /* |x| < 40 */
  81   if (ix < 0x40044000)
  82     {
  83       if (u.value == 0)
  84         return x;               /* x == +- 0 */
  85       if (ix < 0x3fc60000)      /* |x| < 2^-57 */
  86         return x * (one + tiny); /* tanh(small) = small */
  87       u.parts32.w0 = ix;        /* Absolute value of x.  */
  88       if (ix >= 0x3fff0000)
  89         {                       /* |x| >= 1  */
  90           t = __expm1l (two * u.value);
  91           z = one - two / (t + two);
  92         }
  93       else
  94         {
  95           t = __expm1l (-two * u.value);
  96           z = -t / (t + two);
  97         }
  98       /* |x| > 40, return +-1 */
  99     }
 100   else
 101     {
 102       z = one - tiny;           /* raised inexact flag */
 103     }
 104   return (jx & 0x80000000) ? -z : z;
 105 }
 106 weak_alias (__tanhl, tanhl)