1 files changed, 112 insertions, 0 deletions
diff --git a/nuttx/libc/math/lib_expf.c b/nuttx/libc/math/lib_expf.c
new file mode 100644
index 000000000..3e43c54a6
--- /dev/null
+++ b/nuttx/libc/math/lib_expf.c
@@ -0,0 +1,112 @@
+/************************************************************************
+ * libc/math/lib_expf.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 <sys/types.h>
+#include <math.h>
+
+#include "lib_internal.h"
+
+/************************************************************************
+ * Private Data
+ ************************************************************************/
+
+static float _flt_inv_fact[] =
+{
+  1.0 / 1.0,                    // 1/0!
+  1.0 / 1.0,                    // 1/1!
+  1.0 / 2.0,                    // 1/2!
+  1.0 / 6.0,                    // 1/3!
+  1.0 / 24.0,                   // 1/4!
+  1.0 / 120.0,                  // 1/5!
+  1.0 / 720.0,                  // 1/6!
+  1.0 / 5040.0,                 // 1/7!
+  1.0 / 40320.0,                // 1/8!
+  1.0 / 362880.0,               // 1/9!
+  1.0 / 3628800.0,              // 1/10!
+};
+
+/************************************************************************
+ * Public Functions
+ ************************************************************************/
+
+float expf(float x)
+{
+  size_t int_part;
+  bool invert;
+  float value;
+  float x0;
+  size_t i;
+
+  if (x == 0)
+    {
+      return 1;
+    }
+  else if (x < 0)
+    {
+      invert = true;
+      x = -x;
+    }
+  else
+    {
+      invert = false;
+    }
+
+  /* Extract integer component */
+
+  int_part = (size_t) x;
+
+  /* set x to fractional component */
+
+  x -= (float)int_part;
+
+  /* Perform Taylor series approximation with eleven terms */
+
+  value = 0.0;
+  x0 = 1.0;
+  for (i = 0; i < 10; i++)
+    {
+      value += x0 * _flt_inv_fact[i];
+      x0 *= x;
+    }
+
+  /* Multiply by exp of the integer component */
+
+  value *= lib_expi(int_part);
+
+  if (invert)
+    {
+      return (1.0 / value);
+    }
+  else
+    {
+      return value;
+    }
+}