diff --git a/src/main/java/io/github/dsheirer/dsp/fft/MixedRadixComplexFFT.java b/src/main/java/io/github/dsheirer/dsp/fft/MixedRadixComplexFFT.java
new file mode 100644
index 00000000..38213e19
--- /dev/null
+++ b/src/main/java/io/github/dsheirer/dsp/fft/MixedRadixComplexFFT.java
@@ -0,0 +1,779 @@
+/*
+ * *****************************************************************************
+ * Copyright (C) 2014-2026 Dennis Sheirer
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program. If not, see
+ * ****************************************************************************
+ *
+ * The transform kernels in this class are ported from the mixed radix complex FFT (cffti, cfftf and passf2/3/4/5)
+ * in JTransforms org.jtransforms.fft.FloatFFT_1D, which carries the following license:
+ *
+ * JTransforms
+ * Copyright (c) 2007 onward, Piotr Wendykier
+ * 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.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS 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 COPYRIGHT OWNER 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.
+ */
+package io.github.dsheirer.dsp.fft;
+
+/**
+ * Allocation-free mixed radix complex FFT for sizes that factor into 2, 3 and 5 only.
+ *
+ * This is a port of the JTransforms FloatFFT_1D mixed radix complex transform path. JTransforms allocates a new
+ * 2N float scratch array on every mixed radix transform, which creates significant garbage collection pressure when
+ * the transform runs at block rate (e.g. the polyphase channelizer IFFT). This implementation pre-allocates the
+ * scratch buffer once and reuses it for each transform.
+ *
+ * Results match JTransforms FloatFFT_1D complexForward() and complexInverse(): the forward transform uses the
+ * exp(-j...) kernel, the inverse uses exp(+j...), and the inverse optionally scales by 1/N. Twiddle factors are
+ * calculated in double precision, so results can differ from JTransforms in the least significant bits.
+ *
+ * Samples are interleaved complex: a[offset + 2k] = Re[k] and a[offset + 2k + 1] = Im[k] for 0 <= k < N.
+ *
+ * Note: this class is NOT thread-safe since it reuses an internal scratch buffer. Use one instance per thread.
+ */
+public class MixedRadixComplexFFT
+{
+ private static final int[] FACTORS = {4, 2, 3, 5};
+ private static final int FORWARD = -1;
+ private static final int INVERSE = 1;
+
+ private final int mSize;
+ private final int[] mFactors;
+ private final float[] mTwiddles;
+ private final float[] mScratch;
+ private final float mScale;
+
+ /**
+ * Constructs an instance
+ * @param size of the transform in complex samples. Must be a positive value with no prime factors other than
+ * 2, 3 and 5.
+ * @throws IllegalArgumentException if the size is not supported
+ */
+ public MixedRadixComplexFFT(int size)
+ {
+ if(!isSupported(size))
+ {
+ throw new IllegalArgumentException("Unsupported FFT size [" + size +
+ "] - size must be positive and have no prime factors other than 2, 3 and 5");
+ }
+
+ mSize = size;
+ mFactors = factorize(size);
+ mTwiddles = new float[2 * size + 2];
+ mScratch = new float[2 * size];
+ mScale = 1.0f / size;
+ calculateTwiddles();
+ }
+
+ /**
+ * Indicates if the size can be transformed by this class.
+ * @param size in complex samples
+ * @return true if the size is positive and has no prime factors other than 2, 3 and 5.
+ */
+ public static boolean isSupported(int size)
+ {
+ if(size < 1)
+ {
+ return false;
+ }
+
+ int remainder = size;
+
+ for(int factor: new int[]{2, 3, 5})
+ {
+ while(remainder % factor == 0)
+ {
+ remainder /= factor;
+ }
+ }
+
+ return remainder == 1;
+ }
+
+ /**
+ * Size of this transform
+ * @return size in complex samples
+ */
+ public int getSize()
+ {
+ return mSize;
+ }
+
+ /**
+ * Computes the forward DFT of the interleaved complex samples, in place. Equivalent to JTransforms
+ * FloatFFT_1D.complexForward(samples, offset).
+ * @param samples interleaved complex, with at least 2N values from the offset
+ * @param offset to the first sample
+ */
+ public void forward(float[] samples, int offset)
+ {
+ transform(samples, offset, FORWARD);
+ }
+
+ /**
+ * Computes the forward DFT of the interleaved complex samples, in place.
+ * @param samples interleaved complex, with at least 2N values
+ */
+ public void forward(float[] samples)
+ {
+ forward(samples, 0);
+ }
+
+ /**
+ * Computes the inverse DFT of the interleaved complex samples, in place. Equivalent to JTransforms
+ * FloatFFT_1D.complexInverse(samples, offset, scale).
+ * @param samples interleaved complex, with at least 2N values from the offset
+ * @param offset to the first sample
+ * @param scale true to scale the results by 1/N
+ */
+ public void inverse(float[] samples, int offset, boolean scale)
+ {
+ transform(samples, offset, INVERSE);
+
+ if(scale && mSize > 1)
+ {
+ int end = offset + 2 * mSize;
+
+ for(int x = offset; x < end; x++)
+ {
+ samples[x] *= mScale;
+ }
+ }
+ }
+
+ /**
+ * Computes the inverse DFT of the interleaved complex samples, in place.
+ * @param samples interleaved complex, with at least 2N values
+ * @param scale true to scale the results by 1/N
+ */
+ public void inverse(float[] samples, boolean scale)
+ {
+ inverse(samples, 0, scale);
+ }
+
+ /**
+ * Factors the size into the radix sequence used by the transform, ported from JTransforms cffti(). Radix 4 is
+ * preferred, then 2, 3 and 5, and a radix 2 factor is moved to the front of the sequence.
+ */
+ private static int[] factorize(int size)
+ {
+ if(size == 1)
+ {
+ return new int[0];
+ }
+
+ int[] factors = new int[32];
+ int count = 0;
+ int remainder = size;
+
+ for(int factor: FACTORS)
+ {
+ while(remainder % factor == 0)
+ {
+ factors[count++] = factor;
+ remainder /= factor;
+
+ if(factor == 2 && count != 1)
+ {
+ System.arraycopy(factors, 0, factors, 1, count - 1);
+ factors[0] = 2;
+ }
+ }
+ }
+
+ if(remainder != 1)
+ {
+ throw new IllegalArgumentException("Unsupported FFT size [" + size + "]");
+ }
+
+ int[] result = new int[count];
+ System.arraycopy(factors, 0, result, 0, count);
+ return result;
+ }
+
+ /**
+ * Calculates the twiddle factor table, ported from JTransforms cffti() with the table offset removed and the
+ * angles calculated in double precision.
+ */
+ private void calculateTwiddles()
+ {
+ if(mSize == 1)
+ {
+ return;
+ }
+
+ double angleIncrement = 2.0 * Math.PI / mSize;
+ int i = 1;
+ int l1 = 1;
+
+ for(int factor: mFactors)
+ {
+ int ld = 0;
+ int l2 = l1 * factor;
+ int ido = mSize / l2;
+ int idot = ido + ido + 2;
+
+ for(int j = 1; j < factor; j++)
+ {
+ mTwiddles[i - 1] = 1;
+ mTwiddles[i] = 0;
+ ld += l1;
+ int fi = 0;
+ double argld = ld * angleIncrement;
+
+ for(int ii = 4; ii <= idot; ii += 2)
+ {
+ i += 2;
+ fi++;
+ double arg = fi * argld;
+ mTwiddles[i - 1] = (float)Math.cos(arg);
+ mTwiddles[i] = (float)Math.sin(arg);
+ }
+ }
+
+ l1 = l2;
+ }
+ }
+
+ /**
+ * Performs the transform, ported from JTransforms cfftf() using the reusable scratch buffer.
+ * @param a samples
+ * @param offa offset to first sample
+ * @param isign -1 for forward and +1 for inverse
+ */
+ private void transform(float[] a, int offa, int isign)
+ {
+ if(mSize == 1)
+ {
+ return;
+ }
+
+ float[] ch = mScratch;
+ int twon = 2 * mSize;
+ boolean inScratch = false;
+ int l1 = 1;
+ int iw = 0;
+
+ for(int factor: mFactors)
+ {
+ int l2 = factor * l1;
+ int idot = 2 * (mSize / l2);
+
+ switch(factor)
+ {
+ case 4:
+ if(inScratch)
+ {
+ passf4(idot, l1, ch, 0, a, offa, iw, isign);
+ }
+ else
+ {
+ passf4(idot, l1, a, offa, ch, 0, iw, isign);
+ }
+ break;
+ case 2:
+ if(inScratch)
+ {
+ passf2(idot, l1, ch, 0, a, offa, iw, isign);
+ }
+ else
+ {
+ passf2(idot, l1, a, offa, ch, 0, iw, isign);
+ }
+ break;
+ case 3:
+ if(inScratch)
+ {
+ passf3(idot, l1, ch, 0, a, offa, iw, isign);
+ }
+ else
+ {
+ passf3(idot, l1, a, offa, ch, 0, iw, isign);
+ }
+ break;
+ case 5:
+ if(inScratch)
+ {
+ passf5(idot, l1, ch, 0, a, offa, iw, isign);
+ }
+ else
+ {
+ passf5(idot, l1, a, offa, ch, 0, iw, isign);
+ }
+ break;
+ default:
+ throw new IllegalStateException("Unsupported radix: " + factor);
+ }
+
+ inScratch = !inScratch;
+ l1 = l2;
+ iw += (factor - 1) * idot;
+ }
+
+ if(inScratch)
+ {
+ System.arraycopy(ch, 0, a, offa, twon);
+ }
+ }
+
+ /**
+ * Radix 2 butterfly, ported from JTransforms passf2().
+ */
+ private void passf2(final int ido, final int l1, final float[] in, final int in_off, final float[] out,
+ final int out_off, final int offset, final int isign)
+ {
+ final float[] wtable = mTwiddles;
+ int iw1 = offset;
+ int idx = ido * l1;
+
+ if(ido <= 2)
+ {
+ for(int k = 0; k < l1; k++)
+ {
+ int idx0 = k * ido;
+ int iidx1 = in_off + 2 * idx0;
+ int iidx2 = iidx1 + ido;
+ float a1r = in[iidx1];
+ float a1i = in[iidx1 + 1];
+ float a2r = in[iidx2];
+ float a2i = in[iidx2 + 1];
+
+ int oidx1 = out_off + idx0;
+ int oidx2 = oidx1 + idx;
+ out[oidx1] = a1r + a2r;
+ out[oidx1 + 1] = a1i + a2i;
+ out[oidx2] = a1r - a2r;
+ out[oidx2 + 1] = a1i - a2i;
+ }
+ }
+ else
+ {
+ for(int k = 0; k < l1; k++)
+ {
+ for(int i = 0; i < ido - 1; i += 2)
+ {
+ int idx0 = k * ido;
+ int iidx1 = in_off + i + 2 * idx0;
+ int iidx2 = iidx1 + ido;
+ float i1r = in[iidx1];
+ float i1i = in[iidx1 + 1];
+ float i2r = in[iidx2];
+ float i2i = in[iidx2 + 1];
+
+ int widx1 = i + iw1;
+ float w1r = wtable[widx1];
+ float w1i = isign * wtable[widx1 + 1];
+
+ float t1r = i1r - i2r;
+ float t1i = i1i - i2i;
+
+ int oidx1 = out_off + i + idx0;
+ int oidx2 = oidx1 + idx;
+ out[oidx1] = i1r + i2r;
+ out[oidx1 + 1] = i1i + i2i;
+ out[oidx2] = w1r * t1r - w1i * t1i;
+ out[oidx2 + 1] = w1r * t1i + w1i * t1r;
+ }
+ }
+ }
+ }
+
+ /**
+ * Radix 3 butterfly, ported from JTransforms passf3().
+ */
+ private void passf3(final int ido, final int l1, final float[] in, final int in_off, final float[] out,
+ final int out_off, final int offset, final int isign)
+ {
+ final float taur = -0.5f;
+ final float taui = 0.866025403784438707610604524234076962f;
+ final float[] wtable = mTwiddles;
+ int iw1 = offset;
+ int iw2 = iw1 + ido;
+ final int idxt = l1 * ido;
+
+ if(ido == 2)
+ {
+ for(int k = 1; k <= l1; k++)
+ {
+ int iidx1 = in_off + (3 * k - 2) * ido;
+ int iidx2 = iidx1 + ido;
+ int iidx3 = iidx1 - ido;
+ float i1r = in[iidx1];
+ float i1i = in[iidx1 + 1];
+ float i2r = in[iidx2];
+ float i2i = in[iidx2 + 1];
+ float i3r = in[iidx3];
+ float i3i = in[iidx3 + 1];
+
+ float tr2 = i1r + i2r;
+ float cr2 = i3r + taur * tr2;
+ float ti2 = i1i + i2i;
+ float ci2 = i3i + taur * ti2;
+ float cr3 = isign * taui * (i1r - i2r);
+ float ci3 = isign * taui * (i1i - i2i);
+
+ int oidx1 = out_off + (k - 1) * ido;
+ int oidx2 = oidx1 + idxt;
+ int oidx3 = oidx2 + idxt;
+ out[oidx1] = i3r + tr2;
+ out[oidx1 + 1] = i3i + ti2;
+ out[oidx2] = cr2 - ci3;
+ out[oidx2 + 1] = ci2 + cr3;
+ out[oidx3] = cr2 + ci3;
+ out[oidx3 + 1] = ci2 - cr3;
+ }
+ }
+ else
+ {
+ for(int k = 1; k <= l1; k++)
+ {
+ int idx1 = in_off + (3 * k - 2) * ido;
+ int idx2 = out_off + (k - 1) * ido;
+
+ for(int i = 0; i < ido - 1; i += 2)
+ {
+ int iidx1 = i + idx1;
+ int iidx2 = iidx1 + ido;
+ int iidx3 = iidx1 - ido;
+ float a1r = in[iidx1];
+ float a1i = in[iidx1 + 1];
+ float a2r = in[iidx2];
+ float a2i = in[iidx2 + 1];
+ float a3r = in[iidx3];
+ float a3i = in[iidx3 + 1];
+
+ float tr2 = a1r + a2r;
+ float cr2 = a3r + taur * tr2;
+ float ti2 = a1i + a2i;
+ float ci2 = a3i + taur * ti2;
+ float cr3 = isign * taui * (a1r - a2r);
+ float ci3 = isign * taui * (a1i - a2i);
+ float dr2 = cr2 - ci3;
+ float dr3 = cr2 + ci3;
+ float di2 = ci2 + cr3;
+ float di3 = ci2 - cr3;
+
+ int widx1 = i + iw1;
+ int widx2 = i + iw2;
+ float w1r = wtable[widx1];
+ float w1i = isign * wtable[widx1 + 1];
+ float w2r = wtable[widx2];
+ float w2i = isign * wtable[widx2 + 1];
+
+ int oidx1 = i + idx2;
+ int oidx2 = oidx1 + idxt;
+ int oidx3 = oidx2 + idxt;
+ out[oidx1] = a3r + tr2;
+ out[oidx1 + 1] = a3i + ti2;
+ out[oidx2] = w1r * dr2 - w1i * di2;
+ out[oidx2 + 1] = w1r * di2 + w1i * dr2;
+ out[oidx3] = w2r * dr3 - w2i * di3;
+ out[oidx3 + 1] = w2r * di3 + w2i * dr3;
+ }
+ }
+ }
+ }
+
+ /**
+ * Radix 4 butterfly, ported from JTransforms passf4().
+ */
+ private void passf4(final int ido, final int l1, final float[] in, final int in_off, final float[] out,
+ final int out_off, final int offset, final int isign)
+ {
+ final float[] wtable = mTwiddles;
+ int iw1 = offset;
+ int iw2 = iw1 + ido;
+ int iw3 = iw2 + ido;
+ int idx0 = l1 * ido;
+
+ if(ido == 2)
+ {
+ for(int k = 0; k < l1; k++)
+ {
+ int idxt1 = k * ido;
+ int iidx1 = in_off + 4 * idxt1 + 1;
+ int iidx2 = iidx1 + ido;
+ int iidx3 = iidx2 + ido;
+ int iidx4 = iidx3 + ido;
+
+ float i1i = in[iidx1 - 1];
+ float i1r = in[iidx1];
+ float i2i = in[iidx2 - 1];
+ float i2r = in[iidx2];
+ float i3i = in[iidx3 - 1];
+ float i3r = in[iidx3];
+ float i4i = in[iidx4 - 1];
+ float i4r = in[iidx4];
+
+ float ti1 = i1r - i3r;
+ float ti2 = i1r + i3r;
+ float tr4 = i4r - i2r;
+ float ti3 = i2r + i4r;
+ float tr1 = i1i - i3i;
+ float tr2 = i1i + i3i;
+ float ti4 = i2i - i4i;
+ float tr3 = i2i + i4i;
+
+ int oidx1 = out_off + idxt1;
+ int oidx2 = oidx1 + idx0;
+ int oidx3 = oidx2 + idx0;
+ int oidx4 = oidx3 + idx0;
+ out[oidx1] = tr2 + tr3;
+ out[oidx1 + 1] = ti2 + ti3;
+ out[oidx2] = tr1 + isign * tr4;
+ out[oidx2 + 1] = ti1 + isign * ti4;
+ out[oidx3] = tr2 - tr3;
+ out[oidx3 + 1] = ti2 - ti3;
+ out[oidx4] = tr1 - isign * tr4;
+ out[oidx4 + 1] = ti1 - isign * ti4;
+ }
+ }
+ else
+ {
+ for(int k = 0; k < l1; k++)
+ {
+ int idx1 = k * ido;
+ int idx2 = in_off + 1 + 4 * idx1;
+
+ for(int i = 0; i < ido - 1; i += 2)
+ {
+ int iidx1 = i + idx2;
+ int iidx2 = iidx1 + ido;
+ int iidx3 = iidx2 + ido;
+ int iidx4 = iidx3 + ido;
+ float i1i = in[iidx1 - 1];
+ float i1r = in[iidx1];
+ float i2i = in[iidx2 - 1];
+ float i2r = in[iidx2];
+ float i3i = in[iidx3 - 1];
+ float i3r = in[iidx3];
+ float i4i = in[iidx4 - 1];
+ float i4r = in[iidx4];
+
+ float ti1 = i1r - i3r;
+ float ti2 = i1r + i3r;
+ float ti3 = i2r + i4r;
+ float tr4 = i4r - i2r;
+ float tr1 = i1i - i3i;
+ float tr2 = i1i + i3i;
+ float ti4 = i2i - i4i;
+ float tr3 = i2i + i4i;
+ float cr3 = tr2 - tr3;
+ float ci3 = ti2 - ti3;
+ float cr2 = tr1 + isign * tr4;
+ float cr4 = tr1 - isign * tr4;
+ float ci2 = ti1 + isign * ti4;
+ float ci4 = ti1 - isign * ti4;
+
+ int widx1 = i + iw1;
+ int widx2 = i + iw2;
+ int widx3 = i + iw3;
+ float w1r = wtable[widx1];
+ float w1i = isign * wtable[widx1 + 1];
+ float w2r = wtable[widx2];
+ float w2i = isign * wtable[widx2 + 1];
+ float w3r = wtable[widx3];
+ float w3i = isign * wtable[widx3 + 1];
+
+ int oidx1 = out_off + i + idx1;
+ int oidx2 = oidx1 + idx0;
+ int oidx3 = oidx2 + idx0;
+ int oidx4 = oidx3 + idx0;
+ out[oidx1] = tr2 + tr3;
+ out[oidx1 + 1] = ti2 + ti3;
+ out[oidx2] = w1r * cr2 - w1i * ci2;
+ out[oidx2 + 1] = w1r * ci2 + w1i * cr2;
+ out[oidx3] = w2r * cr3 - w2i * ci3;
+ out[oidx3 + 1] = w2r * ci3 + w2i * cr3;
+ out[oidx4] = w3r * cr4 - w3i * ci4;
+ out[oidx4 + 1] = w3r * ci4 + w3i * cr4;
+ }
+ }
+ }
+ }
+
+ /**
+ * Radix 5 butterfly, ported from JTransforms passf5().
+ */
+ private void passf5(final int ido, final int l1, final float[] in, final int in_off, final float[] out,
+ final int out_off, final int offset, final int isign)
+ {
+ final float tr11 = 0.309016994374947451262869435595348477f;
+ final float ti11 = 0.951056516295153531181938433292089030f;
+ final float tr12 = -0.809016994374947340240566973079694435f;
+ final float ti12 = 0.587785252292473248125759255344746634f;
+ final float[] wtable = mTwiddles;
+ int iw1 = offset;
+ int iw2 = iw1 + ido;
+ int iw3 = iw2 + ido;
+ int iw4 = iw3 + ido;
+ int idx0 = l1 * ido;
+
+ if(ido == 2)
+ {
+ for(int k = 1; k <= l1; ++k)
+ {
+ int iidx1 = in_off + (5 * k - 4) * ido + 1;
+ int iidx2 = iidx1 + ido;
+ int iidx3 = iidx1 - ido;
+ int iidx4 = iidx2 + ido;
+ int iidx5 = iidx4 + ido;
+
+ float i1i = in[iidx1 - 1];
+ float i1r = in[iidx1];
+ float i2i = in[iidx2 - 1];
+ float i2r = in[iidx2];
+ float i3i = in[iidx3 - 1];
+ float i3r = in[iidx3];
+ float i4i = in[iidx4 - 1];
+ float i4r = in[iidx4];
+ float i5i = in[iidx5 - 1];
+ float i5r = in[iidx5];
+
+ float ti5 = i1r - i5r;
+ float ti2 = i1r + i5r;
+ float ti4 = i2r - i4r;
+ float ti3 = i2r + i4r;
+ float tr5 = i1i - i5i;
+ float tr2 = i1i + i5i;
+ float tr4 = i2i - i4i;
+ float tr3 = i2i + i4i;
+ float cr2 = i3i + tr11 * tr2 + tr12 * tr3;
+ float ci2 = i3r + tr11 * ti2 + tr12 * ti3;
+ float cr3 = i3i + tr12 * tr2 + tr11 * tr3;
+ float ci3 = i3r + tr12 * ti2 + tr11 * ti3;
+ float cr5 = isign * (ti11 * tr5 + ti12 * tr4);
+ float ci5 = isign * (ti11 * ti5 + ti12 * ti4);
+ float cr4 = isign * (ti12 * tr5 - ti11 * tr4);
+ float ci4 = isign * (ti12 * ti5 - ti11 * ti4);
+
+ int oidx1 = out_off + (k - 1) * ido;
+ int oidx2 = oidx1 + idx0;
+ int oidx3 = oidx2 + idx0;
+ int oidx4 = oidx3 + idx0;
+ int oidx5 = oidx4 + idx0;
+ out[oidx1] = i3i + tr2 + tr3;
+ out[oidx1 + 1] = i3r + ti2 + ti3;
+ out[oidx2] = cr2 - ci5;
+ out[oidx2 + 1] = ci2 + cr5;
+ out[oidx3] = cr3 - ci4;
+ out[oidx3 + 1] = ci3 + cr4;
+ out[oidx4] = cr3 + ci4;
+ out[oidx4 + 1] = ci3 - cr4;
+ out[oidx5] = cr2 + ci5;
+ out[oidx5 + 1] = ci2 - cr5;
+ }
+ }
+ else
+ {
+ for(int k = 1; k <= l1; k++)
+ {
+ int idx1 = in_off + 1 + (k * 5 - 4) * ido;
+ int idx2 = out_off + (k - 1) * ido;
+
+ for(int i = 0; i < ido - 1; i += 2)
+ {
+ int iidx1 = i + idx1;
+ int iidx2 = iidx1 + ido;
+ int iidx3 = iidx1 - ido;
+ int iidx4 = iidx2 + ido;
+ int iidx5 = iidx4 + ido;
+ float i1i = in[iidx1 - 1];
+ float i1r = in[iidx1];
+ float i2i = in[iidx2 - 1];
+ float i2r = in[iidx2];
+ float i3i = in[iidx3 - 1];
+ float i3r = in[iidx3];
+ float i4i = in[iidx4 - 1];
+ float i4r = in[iidx4];
+ float i5i = in[iidx5 - 1];
+ float i5r = in[iidx5];
+
+ float ti5 = i1r - i5r;
+ float ti2 = i1r + i5r;
+ float ti4 = i2r - i4r;
+ float ti3 = i2r + i4r;
+ float tr5 = i1i - i5i;
+ float tr2 = i1i + i5i;
+ float tr4 = i2i - i4i;
+ float tr3 = i2i + i4i;
+ float cr2 = i3i + tr11 * tr2 + tr12 * tr3;
+ float ci2 = i3r + tr11 * ti2 + tr12 * ti3;
+ float cr3 = i3i + tr12 * tr2 + tr11 * tr3;
+ float ci3 = i3r + tr12 * ti2 + tr11 * ti3;
+ float cr5 = isign * (ti11 * tr5 + ti12 * tr4);
+ float ci5 = isign * (ti11 * ti5 + ti12 * ti4);
+ float cr4 = isign * (ti12 * tr5 - ti11 * tr4);
+ float ci4 = isign * (ti12 * ti5 - ti11 * ti4);
+ float dr3 = cr3 - ci4;
+ float dr4 = cr3 + ci4;
+ float di3 = ci3 + cr4;
+ float di4 = ci3 - cr4;
+ float dr5 = cr2 + ci5;
+ float dr2 = cr2 - ci5;
+ float di5 = ci2 - cr5;
+ float di2 = ci2 + cr5;
+
+ int widx1 = i + iw1;
+ int widx2 = i + iw2;
+ int widx3 = i + iw3;
+ int widx4 = i + iw4;
+ float w1r = wtable[widx1];
+ float w1i = isign * wtable[widx1 + 1];
+ float w2r = wtable[widx2];
+ float w2i = isign * wtable[widx2 + 1];
+ float w3r = wtable[widx3];
+ float w3i = isign * wtable[widx3 + 1];
+ float w4r = wtable[widx4];
+ float w4i = isign * wtable[widx4 + 1];
+
+ int oidx1 = i + idx2;
+ int oidx2 = oidx1 + idx0;
+ int oidx3 = oidx2 + idx0;
+ int oidx4 = oidx3 + idx0;
+ int oidx5 = oidx4 + idx0;
+ out[oidx1] = i3i + tr2 + tr3;
+ out[oidx1 + 1] = i3r + ti2 + ti3;
+ out[oidx2] = w1r * dr2 - w1i * di2;
+ out[oidx2 + 1] = w1r * di2 + w1i * dr2;
+ out[oidx3] = w2r * dr3 - w2i * di3;
+ out[oidx3 + 1] = w2r * di3 + w2i * dr3;
+ out[oidx4] = w3r * dr4 - w3i * di4;
+ out[oidx4 + 1] = w3r * di4 + w3i * dr4;
+ out[oidx5] = w4r * dr5 - w4i * di5;
+ out[oidx5 + 1] = w4r * di5 + w4i * dr5;
+ }
+ }
+ }
+ }
+}
diff --git a/src/main/java/io/github/dsheirer/dsp/filter/channelizer/ComplexPolyphaseChannelizerM2.java b/src/main/java/io/github/dsheirer/dsp/filter/channelizer/ComplexPolyphaseChannelizerM2.java
index 707eea94..f82b45dc 100644
--- a/src/main/java/io/github/dsheirer/dsp/filter/channelizer/ComplexPolyphaseChannelizerM2.java
+++ b/src/main/java/io/github/dsheirer/dsp/filter/channelizer/ComplexPolyphaseChannelizerM2.java
@@ -18,6 +18,7 @@
*/
package io.github.dsheirer.dsp.filter.channelizer;
+import io.github.dsheirer.dsp.fft.MixedRadixComplexFFT;
import io.github.dsheirer.dsp.filter.FilterFactory;
import io.github.dsheirer.dsp.filter.design.FilterDesignException;
import io.github.dsheirer.sample.complex.InterleavedComplexSamples;
@@ -27,7 +28,6 @@ import java.util.Arrays;
import java.util.Queue;
import java.util.concurrent.ArrayBlockingQueue;
import org.apache.commons.math3.util.FastMath;
-import org.jtransforms.fft.FloatFFT_1D;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
@@ -85,7 +85,8 @@ public class ComplexPolyphaseChannelizerM2 extends AbstractComplexPolyphaseChann
//Sized to process 40 times per second
private IFFTProcessorDispatcher mIFFTProcessorDispatcher = new IFFTProcessorDispatcher(25);
- private FloatFFT_1D mFFT;
+ //Allocation-free IFFT. Only used by the IFFT processor dispatcher thread since it reuses a scratch buffer.
+ private MixedRadixComplexFFT mFFT;
private ChannelDFT mChannelDFT;
private float[] mInlineSamples;
private float[] mInlineFilter;
@@ -453,7 +454,7 @@ public class ComplexPolyphaseChannelizerM2 extends AbstractComplexPolyphaseChann
private void init(float[] coefficients)
{
int channelCount = getChannelCount();
- mFFT = new FloatFFT_1D(channelCount);
+ mFFT = new MixedRadixComplexFFT(channelCount);
mChannelDFT = ChannelDFTFactory.getChannelDFT(channelCount);
int bufferLength = getSubChannelCount() * mTapsPerChannel;
mSamplesPerBlock = channelCount; //Same as subChannelCount / 2
@@ -505,7 +506,7 @@ public class ComplexPolyphaseChannelizerM2 extends AbstractComplexPolyphaseChann
for(int offset = 0; offset < samples.length; offset += blockLength)
{
//Rotate each of the channels to the correct phase using the IFFT
- mFFT.complexInverse(samples, offset, true);
+ mFFT.inverse(samples, offset, true);
}
}
diff --git a/src/test/java/io/github/dsheirer/dsp/fft/MixedRadixComplexFFTTest.java b/src/test/java/io/github/dsheirer/dsp/fft/MixedRadixComplexFFTTest.java
new file mode 100644
index 00000000..99317d57
--- /dev/null
+++ b/src/test/java/io/github/dsheirer/dsp/fft/MixedRadixComplexFFTTest.java
@@ -0,0 +1,286 @@
+/*
+ * *****************************************************************************
+ * Copyright (C) 2014-2026 Dennis Sheirer
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program. If not, see
+ * ****************************************************************************
+ */
+package io.github.dsheirer.dsp.fft;
+
+import io.github.dsheirer.dsp.filter.channelizer.ComplexPolyphaseChannelizerM2;
+import java.lang.management.ManagementFactory;
+import java.util.Random;
+import org.jtransforms.fft.FloatFFT_1D;
+import org.junit.jupiter.api.Test;
+
+import static org.junit.jupiter.api.Assertions.assertArrayEquals;
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertFalse;
+import static org.junit.jupiter.api.Assertions.assertThrows;
+import static org.junit.jupiter.api.Assertions.assertTrue;
+import static org.junit.jupiter.api.Assumptions.assumeTrue;
+
+/**
+ * Verifies that the MixedRadixComplexFFT produces the same results as JTransforms FloatFFT_1D and does not allocate
+ * memory per transform.
+ */
+public class MixedRadixComplexFFTTest
+{
+ /**
+ * Maximum error relative to the largest output magnitude.
+ */
+ private static final double RELATIVE_TOLERANCE = 2e-6;
+
+ /**
+ * Sizes covering each radix (2, 3, 4, 5), mixed factorizations, powers of two and the channelizer channel counts.
+ */
+ private static final int[] SIZES = {1, 2, 3, 4, 5, 6, 8, 9, 10, 12, 15, 16, 25, 27, 30, 32, 40, 45, 50, 60, 64, 72,
+ 80, 90, 96, 100, 120, 125, 128, 150, 160, 180, 192, 200, 240, 250, 256, 270, 300, 320, 360, 384, 400, 450, 480,
+ 500, 512, 600, 640, 720, 750, 768, 800, 900, 960, 1000, 1024, 1080, 1200, 1500, 2000, 2400, 3000, 4096, 6000};
+
+ private static float[] randomSamples(int length, Random random)
+ {
+ float[] samples = new float[length];
+
+ for(int x = 0; x < samples.length; x++)
+ {
+ samples[x] = random.nextFloat() * 2.0f - 1.0f;
+ }
+
+ return samples;
+ }
+
+ /**
+ * Asserts that the actual values match the expected values within a tolerance relative to the largest expected
+ * magnitude.
+ */
+ private static void assertClose(float[] expected, float[] actual, String message)
+ {
+ assertEquals(expected.length, actual.length, message + " length");
+
+ double maxMagnitude = 1e-30;
+ double maxError = 0;
+
+ for(int x = 0; x < expected.length; x++)
+ {
+ maxMagnitude = Math.max(maxMagnitude, Math.abs(expected[x]));
+ maxError = Math.max(maxError, Math.abs(expected[x] - actual[x]));
+ }
+
+ double relativeError = maxError / maxMagnitude;
+ assertTrue(relativeError <= RELATIVE_TOLERANCE, message + " relative error " + relativeError +
+ " exceeds " + RELATIVE_TOLERANCE);
+ }
+
+ /**
+ * Double precision brute force DFT reference.
+ * @param samples interleaved complex
+ * @param sign -1 forward, +1 inverse
+ */
+ private static float[] referenceDFT(float[] samples, int sign)
+ {
+ int n = samples.length / 2;
+ float[] result = new float[samples.length];
+
+ for(int k = 0; k < n; k++)
+ {
+ double re = 0;
+ double im = 0;
+
+ for(int t = 0; t < n; t++)
+ {
+ double angle = sign * 2.0 * Math.PI * ((long)k * t % n) / n;
+ double cos = Math.cos(angle);
+ double sin = Math.sin(angle);
+ re += samples[2 * t] * cos - samples[2 * t + 1] * sin;
+ im += samples[2 * t] * sin + samples[2 * t + 1] * cos;
+ }
+
+ result[2 * k] = (float)re;
+ result[2 * k + 1] = (float)im;
+ }
+
+ return result;
+ }
+
+ @Test
+ public void forwardMatchesJTransforms()
+ {
+ Random random = new Random(1);
+
+ for(int size : SIZES)
+ {
+ float[] input = randomSamples(2 * size, random);
+ float[] expected = input.clone();
+ new FloatFFT_1D(size).complexForward(expected);
+ float[] actual = input.clone();
+ new MixedRadixComplexFFT(size).forward(actual);
+ assertClose(expected, actual, "Forward size " + size);
+ }
+ }
+
+ @Test
+ public void inverseMatchesJTransforms()
+ {
+ Random random = new Random(2);
+
+ for(int size : SIZES)
+ {
+ for(boolean scale : new boolean[]{true, false})
+ {
+ float[] input = randomSamples(2 * size, random);
+ float[] expected = input.clone();
+ new FloatFFT_1D(size).complexInverse(expected, scale);
+ float[] actual = input.clone();
+ new MixedRadixComplexFFT(size).inverse(actual, scale);
+ assertClose(expected, actual, "Inverse size " + size + " scale " + scale);
+ }
+ }
+ }
+
+ @Test
+ public void matchesDoublePrecisionReference()
+ {
+ Random random = new Random(3);
+
+ for(int size : SIZES)
+ {
+ if(size > 1200)
+ {
+ continue; //Brute force reference is O(N^2)
+ }
+
+ MixedRadixComplexFFT fft = new MixedRadixComplexFFT(size);
+ float[] input = randomSamples(2 * size, random);
+
+ float[] forward = input.clone();
+ fft.forward(forward);
+ assertClose(referenceDFT(input, -1), forward, "Forward reference size " + size);
+
+ float[] inverse = input.clone();
+ fft.inverse(inverse, false);
+ assertClose(referenceDFT(input, 1), inverse, "Inverse reference size " + size);
+ }
+ }
+
+ /**
+ * Mirrors the channelizer usage: repeated in-place inverse transforms of consecutive blocks in a larger array,
+ * reusing a single instance and its scratch buffer. Also verifies that data outside each block is not modified.
+ */
+ @Test
+ public void offsetBlocksMatchJTransforms()
+ {
+ Random random = new Random(4);
+ int blocks = 7;
+
+ for(int size : new int[]{2, 72, 96, 100, 128, 240, 400, 480, 600})
+ {
+ int blockLength = 2 * size;
+ int guard = 3;
+ float[] input = randomSamples(blocks * blockLength + 2 * guard, random);
+
+ float[] expected = input.clone();
+ FloatFFT_1D jtransforms = new FloatFFT_1D(size);
+ float[] actual = input.clone();
+ MixedRadixComplexFFT fft = new MixedRadixComplexFFT(size);
+
+ for(int offset = guard; offset < guard + blocks * blockLength; offset += blockLength)
+ {
+ jtransforms.complexInverse(expected, offset, true);
+ fft.inverse(actual, offset, true);
+ }
+
+ assertClose(expected, actual, "Offset blocks size " + size);
+
+ for(int x = 0; x < guard; x++)
+ {
+ assertEquals(input[x], actual[x], "Leading guard modified size " + size);
+ assertEquals(input[input.length - 1 - x], actual[actual.length - 1 - x],
+ "Trailing guard modified size " + size);
+ }
+ }
+ }
+
+ @Test
+ public void roundTripRestoresInput()
+ {
+ Random random = new Random(5);
+
+ for(int size : SIZES)
+ {
+ MixedRadixComplexFFT fft = new MixedRadixComplexFFT(size);
+ float[] input = randomSamples(2 * size, random);
+ float[] samples = input.clone();
+ fft.forward(samples);
+ fft.inverse(samples, true);
+ assertArrayEquals(input, samples, 1e-5f, "Round trip size " + size);
+ }
+ }
+
+ @Test
+ public void supportsAllChannelizerChannelCounts()
+ {
+ for(double sampleRate = 50_000; sampleRate <= 61_440_000; sampleRate += 25_000)
+ {
+ int channelCount = ComplexPolyphaseChannelizerM2.getChannelCount(sampleRate);
+ assertTrue(MixedRadixComplexFFT.isSupported(channelCount), "Channel count " + channelCount +
+ " for sample rate " + sampleRate);
+ }
+ }
+
+ @Test
+ public void rejectsUnsupportedSizes()
+ {
+ for(int size : new int[]{0, -4, 7, 14, 49, 244, 1001})
+ {
+ assertFalse(MixedRadixComplexFFT.isSupported(size), "Size " + size);
+ assertThrows(IllegalArgumentException.class, () -> new MixedRadixComplexFFT(size), "Size " + size);
+ }
+ }
+
+ /**
+ * Verifies that repeated transforms do not allocate memory, which is the reason this class exists.
+ */
+ @Test
+ public void doesNotAllocatePerTransform()
+ {
+ assumeTrue(ManagementFactory.getThreadMXBean() instanceof com.sun.management.ThreadMXBean);
+ com.sun.management.ThreadMXBean threadMXBean = (com.sun.management.ThreadMXBean)ManagementFactory.getThreadMXBean();
+ assumeTrue(threadMXBean.isThreadAllocatedMemorySupported() && threadMXBean.isThreadAllocatedMemoryEnabled());
+
+ int size = 400;
+ int iterations = 10_000;
+ MixedRadixComplexFFT fft = new MixedRadixComplexFFT(size);
+ float[] samples = randomSamples(2 * size, new Random(6));
+
+ //Warm up so that class loading and JIT compilation are complete before measuring
+ for(int x = 0; x < iterations; x++)
+ {
+ fft.inverse(samples, 0, true);
+ }
+
+ long threadId = Thread.currentThread().threadId();
+ long before = threadMXBean.getThreadAllocatedBytes(threadId);
+
+ for(int x = 0; x < iterations; x++)
+ {
+ fft.inverse(samples, 0, true);
+ }
+
+ long allocated = threadMXBean.getThreadAllocatedBytes(threadId) - before;
+
+ //JTransforms allocates 2N floats (3200 bytes at N=400) per call, about 32 MB for these iterations
+ assertTrue(allocated < 64 * 1024, "Allocated " + allocated + " bytes over " + iterations + " transforms");
+ }
+}
diff --git a/src/test/java/io/github/dsheirer/dsp/filter/channelizer/ComplexPolyphaseChannelizerM2Test.java b/src/test/java/io/github/dsheirer/dsp/filter/channelizer/ComplexPolyphaseChannelizerM2Test.java
index 92472897..2d4977ec 100644
--- a/src/test/java/io/github/dsheirer/dsp/filter/channelizer/ComplexPolyphaseChannelizerM2Test.java
+++ b/src/test/java/io/github/dsheirer/dsp/filter/channelizer/ComplexPolyphaseChannelizerM2Test.java
@@ -19,12 +19,12 @@
package io.github.dsheirer.dsp.filter.channelizer;
+import io.github.dsheirer.dsp.fft.MixedRadixComplexFFT;
import io.github.dsheirer.sample.complex.InterleavedComplexSamples;
import java.util.Arrays;
import java.util.List;
import java.util.Random;
import java.util.concurrent.CopyOnWriteArrayList;
-import org.jtransforms.fft.FloatFFT_1D;
import org.junit.jupiter.api.Test;
import static org.junit.jupiter.api.Assertions.assertEquals;
@@ -142,7 +142,9 @@ public class ComplexPolyphaseChannelizerM2Test
channelizer.stop();
assertEquals(batchCount, batches.size(), "Batches (channelCount=" + channelCount + ")");
- FloatFFT_1D fft = new FloatFFT_1D(channelCount);
+ //Use the same IFFT as the channelizer so the comparison remains bit-exact. Equivalence of this IFFT with
+ //JTransforms is verified separately in MixedRadixComplexFFTTest.
+ MixedRadixComplexFFT fft = new MixedRadixComplexFFT(channelCount);
int blockLength = channelCount * 2;
boolean topBlock = TAPS_PER_CHANNEL % 2 == 0;
@@ -152,7 +154,7 @@ public class ComplexPolyphaseChannelizerM2Test
float[] expected = harness.processFused(topBlock);
topBlock = !topBlock;
harness.shift(channelCount);
- fft.complexInverse(expected, true);
+ fft.inverse(expected, true);
float[] batch = batches.get(block / blocksPerBatch);
int offset = (block % blocksPerBatch) * blockLength;