sysdeps/ieee754/flt-32/s_tanhf.c

   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)