cbrt: Provide replacement on MSVC and Minix.

* lib/math.in.h (cbrt): New declaration.
* lib/cbrt.c: New file.
* m4/cbrt.m4: New file.
* m4/math_h.m4 (gl_MATH_H): Test whether cbrt is declared.
(gl_MATH_H_DEFAULTS): Initialize GNULIB_CBRT, HAVE_CBRT.
* modules/math (Makefile.am): Substitute GNULIB_CBRT, HAVE_CBRT.
* modules/cbrt (Files): Add lib/cbrt.c, m4/cbrt.m4.
(Depends-on): Add dependencies.
(configure.ac): Arrange to compile replacement if HAVE_CBRT is 0.
* tests/test-math-c++.cc: Check the declaration of cbrt.
* doc/posix-functions/cbrt.texi: Mention that the module provides a
replacement.

1 files changed, 71 insertions, 0 deletions

diff --git a/lib/cbrt.c b/lib/cbrt.c
new file mode 100644
index 0000000000..d3659f0a6f
--- /dev/null
+++ b/lib/cbrt.c
@@ -0,0 +1,71 @@
+/* Compute cubic root of double value.
+   Copyright (C) 1997, 2012 Free Software Foundation, Inc.
+
+   Contributed by Dirk Alboth <dirka@uni-paderborn.de> and
+   Ulrich Drepper <drepper@cygnus.com>, 1997.
+
+   This program is free software: you can redistribute it and/or modify
+   it under the terms of the GNU General Public License as published by
+   the Free Software Foundation; either version 3 of the License, or
+   (at your option) any later version.
+
+   This program is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+   GNU General Public License for more details.
+
+   You should have received a copy of the GNU General Public License
+   along with this program.  If not, see <http://www.gnu.org/licenses/>.  */
+
+#include <config.h>
+
+/* Specification.  */
+#include <math.h>
+
+/* Code based on glibc/sysdeps/ieee754/dbl-64/s_cbrt.c.  */
+
+#define CBRT2 1.2599210498948731648             /* 2^(1/3) */
+#define SQR_CBRT2 1.5874010519681994748         /* 2^(2/3) */
+
+static const double factor[5] =
+{
+  1.0 / SQR_CBRT2,
+  1.0 / CBRT2,
+  1.0,
+  CBRT2,
+  SQR_CBRT2
+};
+
+
+double
+cbrt (double x)
+{
+  if (isfinite (x) && x != 0.0)
+    {
+      double xm, ym, u, t2;
+      int xe;
+
+      /* Reduce X.  XM now is an range 1.0 to 0.5.  */
+      xm = frexp (fabs (x), &xe);
+
+      u = (0.354895765043919860
+           + ((1.50819193781584896
+               + ((-2.11499494167371287
+                   + ((2.44693122563534430
+                       + ((-1.83469277483613086
+                           + (0.784932344976639262 - 0.145263899385486377 * xm)
+                             * xm)
+                          * xm))
+                      * xm))
+                  * xm))
+              * xm));
+
+      t2 = u * u * u;
+
+      ym = u * (t2 + 2.0 * xm) / (2.0 * t2 + xm) * factor[2 + xe % 3];
+
+      return ldexp (x > 0.0 ? ym : -ym, xe / 3);
+    }
+  else
+    return x + x;
+}