diff --git a/libc/math/lib_libexpi.c b/libc/math/lib_libexpi.c
index c8f5793d390..c6f8341ae45 100644
--- a/libc/math/lib_libexpi.c
+++ b/libc/math/lib_libexpi.c
@@ -58,7 +58,7 @@
  * Private Data
  ****************************************************************************/
 
-static double _expi_square_tbl[11] =
+static double g_expi_square_tbl[11] =
 {
   M_E,                          /* e^1 */
   M_E2,                         /* e^2 */
@@ -94,7 +94,7 @@ double lib_expi(size_t n)
       if (n & (1 << i))
         {
           n   &= ~(1 << i);
-          val *= _expi_square_tbl[i];
+          val *= g_expi_square_tbl[i];
         }
     }
 
diff --git a/libc/math/lib_libexpif.c b/libc/math/lib_libexpif.c
new file mode 100644
index 00000000000..8d8509c723f
--- /dev/null
+++ b/libc/math/lib_libexpif.c
@@ -0,0 +1,96 @@
+/****************************************************************************
+ * libc/math/lib_libexpif.c
+ *
+ * This file is a part of NuttX:
+ *
+ *   Copyright (C) 2016 Gregory Nutt. All rights reserved.
+ *   Ported by: Darcy Gong/Gregory Nutt
+ *
+ * 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>
+
+/****************************************************************************
+ * Public Functions
+ ****************************************************************************/
+
+/****************************************************************************
+ * Pre-processor Definitions
+ ****************************************************************************/
+
+#define M_E2    (M_E * M_E)
+#define M_E4    (M_E2 * M_E2)
+#define M_E8    (M_E4 * M_E4)
+#define M_E16   (M_E8 * M_E8)
+#define M_E32   (M_E16 * M_E16)
+#define M_E64   (M_E32 * M_E32)
+#define M_E128  (M_E64 * M_E64)
+
+/****************************************************************************
+ * Private Data
+ ****************************************************************************/
+
+static float g_expif_square_tbl[11] =
+{
+  (float)M_E,                   /* e^1 */
+  (float)M_E2,                  /* e^2 */
+  (float)M_E4,                  /* e^4 */
+  (float)M_E8,                  /* e^8 */
+  (float)M_E16,                 /* e^16 */
+  (float)M_E32,                 /* e^32 */
+  (float)M_E64,                 /* e^64 */
+  (float)M_E128,                /* e^128 */
+};
+
+/****************************************************************************
+ * Public Functions
+ ****************************************************************************/
+
+float lib_expif(size_t n)
+{
+  size_t i;
+  float val;
+
+  if (n > 128)
+    {
+      return INFINITY_F;
+    }
+
+  val = 1.0F;
+
+  for (i = 0; n; i++)
+    {
+      if (n & (1 << i))
+        {
+          n   &= ~(1 << i);
+          val *= g_expif_square_tbl[i];
+        }
+    }
+
+  return val;
+}