1 files changed, 18 insertions, 3 deletions
diff --git a/nuttx/libc/math/lib_sinh.c b/nuttx/libc/math/lib_sinh.c
index da79e7cfd..714a52816 100644
--- a/nuttx/libc/math/lib_sinh.c
+++ b/nuttx/libc/math/lib_sinh.c
@@ -3,7 +3,7 @@
  *
  * This file is a part of NuttX:
  *
- *   Copyright (C) 2012 Gregory Nutt. All rights reserved.
+ *   Copyright (C) 2012, 2015 Gregory Nutt. All rights reserved.
  *   Ported by: Darcy Gong
  *
  * It derives from the Rhombs OS math library by Nick Johnson which has
@@ -41,7 +41,22 @@
 #ifdef CONFIG_HAVE_DOUBLE
 double sinh(double x)
 {
-  x = exp(x);
-  return ((x - (1.0 / x)) / 2.0);
+  double y;
+  double z;
+
+  if (fabs(x) < 1E-5)
+    {
+      /* x + 1/3! * x^3 + 1/5! * x^5 + 1/7! * x^7 + ... */
+
+      z = x * x;
+      y = x * (1.0 + z / 6.0);
+    }
+  else
+    {
+      z = exp(x);
+      y = (z - 1.0 / z) / 2.0;
+    }
+
+  return y;
 }
 #endif