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git-svn-id: svn://svn.code.sf.net/p/nuttx/code/trunk@5330 42af7a65-404d-4744-a932-0658087f49c3
2026-06-06 08:36:24 +08:00 · 2012-11-10 16:19:12 +00:00
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+/************************************************************************
+ * lib/math/lib_expl.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 <sys/types.h>
+#include <math.h>
+
+#include "lib_internal.h"
+
+#ifdef CONFIG_HAVE_LONG_DOUBLE
+
+/************************************************************************
+ * Private Data
+ ************************************************************************/
+
+static long double _ldbl_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!
+  1.0 / 39916800.0,             // 1 / 11!
+  1.0 / 479001600.0,            // 1 / 12!
+  1.0 / 6227020800.0,           // 1 / 13!
+  1.0 / 87178291200.0,          // 1 / 14!
+  1.0 / 1307674368000.0,        // 1 / 15!
+  1.0 / 20922789888000.0,       // 1 / 16!
+  1.0 / 355687428096000.0,      // 1 / 17!
+  1.0 / 6402373705728000.0,     // 1 / 18!
+};
+
+/************************************************************************
+ * Public Functions
+ ************************************************************************/
+
+long double expl(long double x)
+{
+  size_t int_part;
+  bool invert;
+  long double value;
+  long double 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 -= (long double)int_part;
+
+  /* Perform Taylor series approximation with nineteen terms */
+
+  value = 0.0;
+  x0 = 1.0;
+  for (i = 0; i < 19; i++)
+    {
+      value += x0 * _ldbl_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;
+    }
+}
+#endif