New module 'cbrtf'.

* lib/math.in.h (cbrtf): New declaration.
* lib/cbrtf.c: New file.
* m4/cbrtf.m4: New file.
* m4/math_h.m4 (gl_MATH_H): Test whether cbrtf is declared.
(gl_MATH_H_DEFAULTS): Initialize GNULIB_CBRTF, HAVE_CBRTF,
HAVE_DECL_CBRTF.
* modules/math (Makefile.am): Substitute GNULIB_CBRTF, HAVE_CBRTF,
HAVE_DECL_CBRTF.
* modules/cbrtf: New file.
* tests/test-math-c++.cc: Check the declaration of cbrtf.
* doc/posix-functions/cbrtf.texi: Mention the new module.

1 files changed, 62 insertions, 0 deletions

diff --git a/lib/cbrtf.c b/lib/cbrtf.c
new file mode 100644
index 0000000000..6320d0e6bc
--- /dev/null
+++ b/lib/cbrtf.c
@@ -0,0 +1,62 @@
+/* Compute cubic root of float 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/flt-32/s_cbrtf.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
+};
+
+
+float
+cbrtf (float x)
+{
+  if (isfinite (x) && x != 0.0f)
+    {
+      float xm, ym, u, t2;
+      int xe;
+
+      /* Reduce X.  XM now is an range 1.0 to 0.5.  */
+      xm = frexpf (fabsf (x), &xe);
+
+      u = (0.492659620528969547
+           + (0.697570460207922770 - 0.191502161678719066 * xm) * xm);
+
+      t2 = u * u * u;
+
+      ym = u * (t2 + 2.0 * xm) / (2.0 * t2 + xm) * factor[2 + xe % 3];
+
+      return ldexpf (x > 0.0 ? ym : -ym, xe / 3);
+    }
+  else
+    return x + x;
+}