lib/libm/src/s_tanhf.c

   1 /* s_tanhf.c -- float version of s_tanh.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: s_tanhf.c,v 1.7 2002/05/26 22:01:59 wiz Exp $
  16  * $DragonFly: src/lib/libm/src/s_tanhf.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 one=1.0, two=2.0, tiny = 1.0e-30;
  23
  24 float
  25 tanhf(float x)
  26 {
  27         float t,z;
  28         int32_t jx,ix;
  29
  30         GET_FLOAT_WORD(jx,x);
  31         ix = jx&0x7fffffff;
  32
  33     /* x is INF or NaN */
  34         if(ix>=0x7f800000) {
  35             if (jx>=0) return one/x+one;    /* tanh(+-inf)=+-1 */
  36             else       return one/x-one;    /* tanh(NaN) = NaN */
  37         }
  38
  39     /* |x| < 22 */
  40         if (ix < 0x41b00000) {          /* |x|<22 */
  41             if (ix<0x24000000)          /* |x|<2**-55 */
  42                 return x*(one+x);       /* tanh(small) = small */
  43             if (ix>=0x3f800000) {       /* |x|>=1  */
  44                 t = expm1f(two*fabsf(x));
  45                 z = one - two/(t+two);
  46             } else {
  47                 t = expm1f(-two*fabsf(x));
  48                 z= -t/(t+two);
  49             }
  50     /* |x| > 22, return +-1 */
  51         } else {
  52             z = one - tiny;             /* raised inexact flag */
  53         }
  54         return (jx>=0)? z: -z;
  55 }