1 files changed, 101 insertions, 0 deletions
diff --git a/nuttx/lib/math/lib_sqrtl.c b/nuttx/lib/math/lib_sqrtl.c
new file mode 100644
index 000000000..f305092e7
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+++ b/nuttx/lib/math/lib_sqrtl.c
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+/************************************************************************
+ * lib/math/lib_sqrtl.c
+ *
+ * This file is a part of NuttX:
+ *
+ *   Copyright (C) 2012 Gregory Nutt. All rights reserved.
+ *   Ported by: Darcy Gong
+ *
+ * It derives from the Rhombs OS math library by Nick Johnson which has
+ * a compatibile, MIT-style license:
+ *
+ * Copyright (C) 2009-2011 Nick Johnson <nickbjohnson4224 at gmail.com>
+ * 
+ * Permission to use, copy, modify, and distribute this software for any
+ * purpose with or without fee is hereby granted, provided that the above
+ * copyright notice and this permission notice appear in all copies.
+ * 
+ * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+ * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
+ * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+ * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+ * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
+ * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
+ * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+ *
+ ************************************************************************/
+
+/************************************************************************
+ * Included Files
+ ************************************************************************/
+
+#include <nuttx/config.h>
+#include <nuttx/compiler.h>
+
+#include <math.h>
+#include <errno.h>
+
+#include "lib_internal.h"
+
+/************************************************************************
+ * Public Functions
+ ************************************************************************/
+
+#if CONFIG_HAVE_LONG_DOUBLE
+long double sqrtl(long double x)
+{
+  long double y, y1;
+
+  /* Filter out invalid/trivial inputs */
+
+  if (x < 0.0)
+    {
+      errno = EDOM;
+      return NAN;
+    }
+
+  if (isnan(x))
+    {
+    return NAN;
+    }
+
+  if (isinf(x))
+    {
+    return INFINITY;
+    }
+
+  if (x == 0.0)
+    {
+    return 0.0;
+    }
+
+  /* Guess square root (using bit manipulation) */
+
+  y = lib_sqrtapprox(x);
+
+  /* Perform four iterations of approximation.  This number (4) is
+   * definitely optimal
+   */
+
+  y = 0.5 * (y + x / y);
+  y = 0.5 * (y + x / y);
+  y = 0.5 * (y + x / y);
+  y = 0.5 * (y + x / y);
+
+  /* If guess was terribe (out of range of float).  Repeat approximation
+   * until convergence
+   */
+
+  if (y * y < x - 1.0 || y * y > x + 1.0)
+    {
+      y1 = -1.0;
+      while (y != y1)
+        {
+          y1 = y;
+          y = 0.5 * (y + x / y);
+        }
+    }
+
+  return y;
+}
+#endif