1  /* s_tanhf.c -- float version of s_tanh.c.
       2   */
       3  
       4  /*
       5   * ====================================================
       6   * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
       7   *
       8   * Developed at SunPro, a Sun Microsystems, Inc. business.
       9   * Permission to use, copy, modify, and distribute this
      10   * software is freely granted, provided that this notice
      11   * is preserved.
      12   * ====================================================
      13   */
      14  
      15  #if defined(LIBM_SCCS) && !defined(lint)
      16  static char rcsid[] = "$NetBSD: s_tanhf.c,v 1.4 1995/05/10 20:48:24 jtc Exp $";
      17  #endif
      18  
      19  #include <float.h>
      20  #include <math.h>
      21  #include <math_private.h>
      22  #include <math-underflow.h>
      23  #include <libm-alias-float.h>
      24  
      25  static const float one=1.0, two=2.0, tiny = 1.0e-30;
      26  
      27  float __tanhf(float x)
      28  {
      29  	float t,z;
      30  	int32_t jx,ix;
      31  
      32  	GET_FLOAT_WORD(jx,x);
      33  	ix = jx&0x7fffffff;
      34  
      35      /* x is INF or NaN */
      36  	if(ix>=0x7f800000) {
      37  	    if (jx>=0) return one/x+one;    /* tanh(+-inf)=+-1 */
      38  	    else       return one/x-one;    /* tanh(NaN) = NaN */
      39  	}
      40  
      41      /* |x| < 22 */
      42  	if (ix < 0x41b00000) {		/* |x|<22 */
      43  	    if (ix == 0)
      44  		return x;		/* x == +-0 */
      45  	    if (ix<0x24000000) 		/* |x|<2**-55 */
      46  	      {
      47  		math_check_force_underflow (x);
      48  		return x*(one+x);    	/* tanh(small) = small */
      49  	      }
      50  	    if (ix>=0x3f800000) {	/* |x|>=1  */
      51  		t = __expm1f(two*fabsf(x));
      52  		z = one - two/(t+two);
      53  	    } else {
      54  	        t = __expm1f(-two*fabsf(x));
      55  	        z= -t/(t+two);
      56  	    }
      57      /* |x| > 22, return +-1 */
      58  	} else {
      59  	    z = one - tiny;		/* raised inexact flag */
      60  	}
      61  	return (jx>=0)? z: -z;
      62  }
      63  libm_alias_float (__tanh, tanh)