50  *
  51  *      Note: 22 was chosen so that fl(1.0+2/(expm1(2*22)+2)) == 1.
  52  *
  53  * Special cases:
  54  *      tanh(NaN) is NaN;
  55  *      only tanh(0)=0 is exact for finite argument.
  56  */
  57 
  58 #include "libm.h"
  59 #include "libm_protos.h"
  60 #include <math.h>
  61 
  62 static const double
  63         one = 1.0,
  64         two = 2.0,
  65         small = 1.0e-10,
  66         big = 1.0e10;
  67 /* INDENT ON */
  68 
  69 double
  70 tanh(double x) {

  71         double t, y, z;
  72         int signx;
  73         volatile double dummy __unused;
  74 
  75         if (isnan(x))
  76                 return (x * x); /* + -> * for Cheetah */
  77         signx = signbit(x);
  78         t = fabs(x);
  79         z = one;
  80         if (t <= 22.0) {
  81                 if (t > one)
  82                         z = one - two / (expm1(t + t) + two);
  83                 else if (t > small) {
  84                         y = expm1(-t - t);
  85                         z = -y / (y + two);
  86                 } else {
  87                         /* raise the INEXACT flag for non-zero t */
  88                         dummy = t + big;
  89 #ifdef lint
  90                         dummy = dummy;
  91 #endif
  92                         return (x);
  93                 }
  94         } else if (!finite(t))
  95                 return (copysign(1.0, x));
  96         else
  97                 return (signx == 1 ? -z + small * small : z - small * small);
  98 
  99         return (signx == 1 ? -z : z);
 100 }

  50  *
  51  *      Note: 22 was chosen so that fl(1.0+2/(expm1(2*22)+2)) == 1.
  52  *
  53  * Special cases:
  54  *      tanh(NaN) is NaN;
  55  *      only tanh(0)=0 is exact for finite argument.
  56  */
  57 
  58 #include "libm.h"
  59 #include "libm_protos.h"
  60 #include <math.h>
  61 
  62 static const double
  63         one = 1.0,
  64         two = 2.0,
  65         small = 1.0e-10,
  66         big = 1.0e10;
  67 /* INDENT ON */
  68 
  69 double
  70 tanh(double x)
  71 {
  72         double t, y, z;
  73         int signx;
  74         volatile double dummy __unused;
  75 
  76         if (isnan(x))
  77                 return (x * x); /* + -> * for Cheetah */
  78         signx = signbit(x);
  79         t = fabs(x);
  80         z = one;
  81         if (t <= 22.0) {
  82                 if (t > one)
  83                         z = one - two / (expm1(t + t) + two);
  84                 else if (t > small) {
  85                         y = expm1(-t - t);
  86                         z = -y / (y + two);
  87                 } else {
  88                         /* raise the INEXACT flag for non-zero t */
  89                         dummy = t + big;
  90 #ifdef lint
  91                         dummy = dummy;
  92 #endif
  93                         return (x);
  94                 }
  95         } else if (!finite(t))
  96                 return (copysign(1.0, x));
  97         else
  98                 return ((signx != 0) ? -z + small * small : z - small * small);
  99 
 100         return ((signx != 0) ? -z : z);
 101 }