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
  16 #include <sys/cdefs.h>
  17 #if defined(LIBM_SCCS) && !defined(lint)
  18 __RCSID("$NetBSD: s_tanhf.c,v 1.7 2002/05/26 22:01:59 wiz Exp $");
  19 #endif
  20
  21 #include "math.h"
  22 #include "math_private.h"
  23
  24 static const float one=1.0, two=2.0, tiny = 1.0e-30;
  25
  26 float
  27 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<0x24000000)          /* |x|<2**-55 */
  44                 return x*(one+x);       /* tanh(small) = small */
  45             if (ix>=0x3f800000) {       /* |x|>=1  */
  46                 t = expm1f(two*fabsf(x));
  47                 z = one - two/(t+two);
  48             } else {
  49                 t = expm1f(-two*fabsf(x));
  50                 z= -t/(t+two);
  51             }
  52     /* |x| > 22, return +-1 */
  53         } else {
  54             z = one - tiny;             /* raised inexact flag */
  55         }
  56         return (jx>=0)? z: -z;
  57 }