Standard Libraries for EDK II.

[mirror_edk2.git] / StdLib / LibC / Math / s_tanh.c

/* @(#)s_tanh.c 5.1 93/09/24 */\r
/*\r
 * ====================================================\r
 * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.\r
 *\r
 * Developed at SunPro, a Sun Microsystems, Inc. business.\r
 * Permission to use, copy, modify, and distribute this\r
 * software is freely granted, provided that this notice\r
 * is preserved.\r
 * ====================================================\r
 */\r
#include  <LibConfig.h>\r
#include  <sys/EfiCdefs.h>\r
#if defined(LIBM_SCCS) && !defined(lint)\r
__RCSID("$NetBSD: s_tanh.c,v 1.10 2002/05/26 22:01:59 wiz Exp $");\r
#endif\r
\r
/* Tanh(x)\r
 * Return the Hyperbolic Tangent of x\r
 *\r
 * Method :\r
 *               x    -x\r
 *              e  - e\r
 *  0. tanh(x) is defined to be -----------\r
 *               x    -x\r
 *              e  + e\r
 *  1. reduce x to non-negative by tanh(-x) = -tanh(x).\r
 *  2.  0      <= x <= 2**-55 : tanh(x) := x*(one+x)\r
 *                  -t\r
 *      2**-55 <  x <=  1     : tanh(x) := -----; t = expm1(-2x)\r
 *                 t + 2\r
 *                 2\r
 *      1      <= x <=  22.0  : tanh(x) := 1-  ----- ; t=expm1(2x)\r
 *               t + 2\r
 *      22.0   <  x <= INF    : tanh(x) := 1.\r
 *\r
 * Special cases:\r
 *  tanh(NaN) is NaN;\r
 *  only tanh(0)=0 is exact for finite argument.\r
 */\r
\r
#include "math.h"\r
#include "math_private.h"\r
\r
static const double one=1.0, two=2.0, tiny = 1.0e-300;\r
\r
double\r
tanh(double x)\r
{\r
  double t,z;\r
  int32_t jx,ix;\r
\r
    /* High word of |x|. */\r
  GET_HIGH_WORD(jx,x);\r
  ix = jx&0x7fffffff;\r
\r
    /* x is INF or NaN */\r
  if(ix>=0x7ff00000) {\r
      if (jx>=0) return one/x+one;    /* tanh(+-inf)=+-1 */\r
      else       return one/x-one;    /* tanh(NaN) = NaN */\r
  }\r
\r
    /* |x| < 22 */\r
  if (ix < 0x40360000) {    /* |x|<22 */\r
      if (ix<0x3c800000)    /* |x|<2**-55 */\r
    return x*(one+x);     /* tanh(small) = small */\r
      if (ix>=0x3ff00000) { /* |x|>=1  */\r
    t = expm1(two*fabs(x));\r
    z = one - two/(t+two);\r
      } else {\r
          t = expm1(-two*fabs(x));\r
          z= -t/(t+two);\r
      }\r
    /* |x| > 22, return +-1 */\r
  } else {\r
      z = one - tiny;   /* raised inexact flag */\r
  }\r
  return (jx>=0)? z: -z;\r
}\r