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diff --git a/nuttx/lib/math/lib_libsqrtapprox.c b/nuttx/lib/math/lib_libsqrtapprox.c
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+/************************************************************************
+ * lib/math/lib_libsqrtapprox.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 <stdint.h>
+#include <math.h>
+
+/************************************************************************
+ * Public Functions
+ ************************************************************************/
+
+float lib_sqrtapprox(float x)
+{
+  int32_t i;
+
+  /* Floats + bit manipulation = +inf fun! */
+
+  i = *((int32_t *) & x);
+  i = 0x1fc00000 + (i >> 1);
+  x = *((float *)&i);
+
+  return x;
+}