Rename jerry-libm to jerry-math (#4410)

That "libm" in the name of the library resulted in awkward naming
on *nix systems (`libjerry-libm.*`, "lib" occurring twice). And the
name of the corresponding header is `math.h` anyway.

Note that this is a breaking change in some sense. The commit
contains no API change, but the build system does change for users
of the math library.

JerryScript-DCO-1.0-Signed-off-by: Akos Kiss akiss@inf.u-szeged.hu

jerry-math/tanh.c

@@ -0,0 +1,117 @@
+/* Copyright JS Foundation and other contributors, http://js.foundation
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ * This file is based on work under the following copyright and permission
+ * notice:
+ *
+ *     Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
+ *
+ *     Developed at SunSoft, a Sun Microsystems, Inc. business.
+ *     Permission to use, copy, modify, and distribute this
+ *     software is freely granted, provided that this notice
+ *     is preserved.
+ *
+ *     @(#)s_tanh.c 1.3 95/01/18
+ */
+
+#include "jerry-math-internal.h"
+
+/* tanh(x)
+ * Return the Hyperbolic Tangent of x
+ *
+ * Method:
+ *                                 x   -x
+ *                                e -  e
+ *  0. tanh(x) is defined to be -----------
+ *                                 x    -x
+ *                                e  +  e
+ *
+ *  1. reduce x to non-negative by tanh(-x) = -tanh(x).
+ *  2.  0      <= x <= 2**-55 : tanh(x) := x * (one + x)
+ *
+ *                                          -t
+ *      2**-55 <  x <=  1     : tanh(x) := -----; t = expm1(-2x)
+ *                                         t + 2
+ *
+ *                                               2
+ *      1      <= x <=  22.0  : tanh(x) := 1-  ----- ; t = expm1(2x)
+ *                                             t + 2
+ *
+ *      22.0   <  x <= INF    : tanh(x) := 1.
+ *
+ * Special cases:
+ *  tanh(NaN) is NaN;
+ *  only tanh(0) = 0 is exact for finite x.
+ */
+#define one 1.0
+#define two 2.0
+#define tiny 1.0e-300
+
+double
+tanh (double x)
+{
+  double t, z;
+  int jx, ix;
+
+  /* High word of |x|. */
+  jx = __HI (x);
+  ix = jx & 0x7fffffff;
+
+  /* x is INF or NaN */
+  if (ix >= 0x7ff00000)
+  {
+    if (jx >= 0)
+    {
+      /* tanh(+-inf) = +-1 */
+      return one / x + one;
+    }
+    else
+    {
+      /* tanh(NaN) = NaN */
+      return one / x - one;
+    }
+  }
+
+  /* |x| < 22 */
+  if (ix < 0x40360000)
+  {
+    /* |x| < 2**-55 */
+    if (ix < 0x3c800000)
+    {
+      /* tanh(small) = small */
+      return x * (one + x);
+    }
+    if (ix >= 0x3ff00000)
+    {
+      /* |x| >= 1  */
+      t = expm1 (two * fabs (x));
+      z = one - two / (t + two);
+    }
+    else
+    {
+      t = expm1 (-two * fabs (x));
+      z = -t / (t + two);
+    }
+  }
+  else
+  {
+    /* |x| > 22, return +-1 */
+    z = one - tiny; /* raised inexact flag */
+  }
+  return (jx >= 0) ? z : -z;
+} /* tanh */
+
+#undef one
+#undef two
+#undef tiny