diff --git a/core/lib/ifft.c b/core/lib/ifft.c
new file mode 100644
index 000000000..c185233e2
--- /dev/null
+++ b/core/lib/ifft.c
@@ -0,0 +1,162 @@
+/*
+ * Copyright (c) 2008, Swedish Institute of Computer Science
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in the
+ *    documentation and/or other materials provided with the distribution.
+ * 3. Neither the name of the Institute nor the names of its contributors
+ *    may be used to endorse or promote products derived from this software
+ *    without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE INSTITUTE AND CONTRIBUTORS ``AS IS'' AND
+ * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED.  IN NO EVENT SHALL THE INSTITUTE OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
+ * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
+ * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
+ * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
+ * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+ * SUCH DAMAGE.
+ *
+ * -----------------------------------------------------------------
+ * ifft - Integer FFT (fast fourier transform) library
+ *
+ *
+ * Author  : Joakim Eriksson
+ * Created : 2008-03-27
+ * Updated : $Date: 2008/03/27 12:12:24 $
+ *           $Revision: 1.1 $
+ */
+#include "lib/ifft.h"
+
+/*---------------------------------------------------------------------------*/
+/* constant table of sin values in 8/7 bits resolution */
+/* NOTE: symmetry can be used to reduce this to 1/2 or 1/4 the size */
+#define SIN_TAB_LEN 120
+#define RESOLUTION 7
+#define ABS(x) (x < 0 ? -x : x)
+
+static const int8_t SIN_TAB[] = {
+ 0,6,13,20,26,33,39,45,52,58,63,69,75,80,
+ 85,90,95,99,103,107,110,114,116,119,121,
+ 123,125,126,127,127,127,127,127,126,125,
+ 123,121,119,116,114,110,107,103,99,95,90,
+ 85,80,75,69,63,58,52,45,39,33,26,20,13,6,
+ 0,-6,-13,-20,-26,-33,-39,-45,-52,-58,-63,
+ -69,-75,-80,-85,-90,-95,-99,-103,-107,-110,
+ -114,-116,-119,-121,-123,-125,-126,-127,-127,
+ -127,-127,-127,-126,-125,-123,-121,-119,-116,
+ -114,-110,-107,-103,-99,-95,-90,-85,-80,-75,
+ -69,-63,-58,-52,-45,-39,-33,-26,-20,-13,-6
+};
+
+
+static uint16_t bitrev(uint16_t j, uint16_t nu) {
+  uint16_t k;
+  k = 0;
+  for (; nu > 0; nu--) {
+    k  = (k << 1) + (j & 1);
+    j = j >> 1;
+  }
+  return k;
+}
+
+
+/* Non interpolating sine... which takes an angle of 0 - 999 */
+static int16_t sinI(uint16_t angleMilli) {
+  uint16_t pos;
+  pos = (uint16_t) ((SIN_TAB_LEN * (uint32_t) angleMilli) / 1000);
+  return SIN_TAB[pos % SIN_TAB_LEN];
+}
+
+static int16_t cosI(uint16_t angleMilli) {
+  return sinI(angleMilli + 250);
+}
+
+static uint16_t log2(uint16_t val) {
+  uint16_t log;
+  log = 0;
+  val = val >> 1; /* The 20 = 1 => log = 0 => val = 0 */
+  while (val > 0) {
+    val = val >> 1;
+    log++;
+  }
+  return log;
+}
+
+
+/* ifft(xre[], n) - integer (fixpoint) version of Fast Fourier Transform
+   An integer version of FFT that takes in-samples in an int16_t array
+   and does an fft on n samples in the array.
+   The result of the FFT is stored in the same array as the samples
+   was stored.
+
+   Note: This fft is designed to be used with 8 bit values (e.g. not
+   16 bit values). The reason for the int16_t array is for keeping some
+   'room' for the calculations. It is also designed for doing fairly small
+   FFT:s since to large sample arrays might cause it to overflow during
+   calculations.
+*/
+void ifft(int16_t xre[], uint16_t n) {
+  uint16_t nu;
+  uint16_t n2;
+  uint16_t nu1;
+  int16_t xim[n];
+  int p, k, l, i;
+  int32_t c, s, tr, ti;
+
+  nu = log2(n);
+  nu1 = nu - 1;
+  n2 = n / 2;
+
+  for (i = 0; i < n; i++)
+    xim[i] = 0;
+
+  for (l = 1; l <= nu; l++) {
+    for (k = 0; k < n; k += n2) {
+      for (i = 1; i <= n2; i++) {
+	p = bitrev(k >> nu1, nu);
+	c = cosI((1000 * p) / n);
+	s = sinI((1000 * p) / n);
+
+	tr = ((xre[k + n2] * c + xim[k + n2] * s) >> RESOLUTION);
+	ti = ((xim[k + n2] * c - xre[k + n2] * s) >> RESOLUTION);
+
+	xre[k + n2] = xre[k] - tr;
+	xim[k + n2] = xim[k] - ti;
+	xre[k] += tr;
+	xim[k] += ti;
+	k++;
+      }
+    }
+    nu1--;
+    n2 = n2 / 2;
+  }
+
+  for (k = 0; k < n; k++) {
+    p = bitrev(k, nu);
+    if (p > k) {
+      n2 = xre[k];
+      xre[k] = xre[p];
+      xre[p] = n2;
+
+      n2 = xim[k];
+      xim[k] = xim[p];
+      xim[p] = n2;
+    }
+  }
+
+  /* This is a fast but not 100% correct magnitude calculation */
+  /* Should be sqrt(xre[i]^2 + xim[i]^2) and normalized with div. by n */
+  for (i = 0, n2 = n / 2; i < n2; i++) {
+    xre[i] = (ABS(xre[i]) + ABS(xim[i]));
+  }
+}
diff --git a/core/lib/ifft.h b/core/lib/ifft.h
new file mode 100644
index 000000000..a18b02062
--- /dev/null
+++ b/core/lib/ifft.h
@@ -0,0 +1,58 @@
+/*
+ * Copyright (c) 2008, Swedish Institute of Computer Science
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in the
+ *    documentation and/or other materials provided with the distribution.
+ * 3. Neither the name of the Institute nor the names of its contributors
+ *    may be used to endorse or promote products derived from this software
+ *    without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE INSTITUTE AND CONTRIBUTORS ``AS IS'' AND
+ * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED.  IN NO EVENT SHALL THE INSTITUTE OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
+ * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
+ * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
+ * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
+ * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+ * SUCH DAMAGE.
+ *
+ * -----------------------------------------------------------------
+ * ifft - Integer FFT (fast fourier transform) library
+ *
+ *
+ *
+ * Author  : Joakim Eriksson
+ * Created : 2008-03-27
+ * Updated : $Date: 2008/03/27 12:12:24 $
+ *           $Revision: 1.1 $
+ */
+
+#ifndef IFFT_H
+#define IFFT_H
+#include "contiki-conf.h"
+
+/* ifft(xre[], n) - integer (fixpoint) version of Fast Fourier Transform
+   An integer version of FFT that takes in-samples in an int16_t array
+   and does an fft on n samples in the array.
+   The result of the FFT is stored in the same array as the samples
+   was stored.
+
+   Note: This fft is designed to be used with 8 bit values (e.g. not
+   16 bit values). The reason for the int16_t array is for keeping some
+   'room' for the calculations. It is also designed for doing fairly small
+   FFT:s since to large sample arrays might cause it to overflow during
+   calculations.
+*/
+void ifft(int16_t xre[], uint16_t n);
+
+#endif /* IFFT_H */