1 files changed, 82 insertions, 0 deletions
diff --git a/nuttx/libc/math/lib_log.c b/nuttx/libc/math/lib_log.c
new file mode 100644
index 000000000..7156f6b41
--- /dev/null
+++ b/nuttx/libc/math/lib_log.c
@@ -0,0 +1,82 @@
+/************************************************************************
+ * libc/math/lib_log.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, 2010 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 <float.h>
+
+/************************************************************************
+ * Public Functions
+ ************************************************************************/
+
+#ifdef CONFIG_HAVE_DOUBLE
+double log(double x)
+{
+  double y, y_old, ey, epsilon;
+
+  y = 0.0;
+  y_old = 1.0;
+  epsilon = DBL_EPSILON;
+
+  while (y > y_old + epsilon || y < y_old - epsilon)
+    {
+      y_old = y;
+      ey = exp(y);
+      y -= (ey - x) / ey;
+
+      if (y > 700.0)
+        {
+          y = 700.0;
+        }
+
+      if (y < -700.0)
+        {
+          y = -700.0;
+        }
+
+      epsilon = (fabs(y) > 1.0) ? fabs(y) * DBL_EPSILON : DBL_EPSILON;
+    }
+
+  if (y == 700.0)
+    {
+      return INFINITY;
+    }
+
+  if (y == -700.0)
+    {
+      return INFINITY;
+    }
+
+  return y;
+}
+#endif