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#2567 Reduces memory overhead by extending the JTransforms FFT package to reuse its float array when calculaing the inverse FFT in the channelizer for a subset of the FFT size operations. (#2568)

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Co-authored-by: sheirerd <sheirerd@ainfosec.com>
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Denny Sheirer
2026-11-03 05:49:40 -05:00
committed by GitHub
parent 0b3ce66cad
commit 1c097491d9
4 changed files with 1075 additions and 7 deletions
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/*
* *****************************************************************************
* 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 <http://www.gnu.org/licenses/>
* ****************************************************************************
*
* 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;
}
}
}
}
}

9
src/main/java/io/github/dsheirer/dsp/filter/channelizer/ComplexPolyphaseChannelizerM2.java
View File

@@ -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);
}
}

286
src/test/java/io/github/dsheirer/dsp/fft/MixedRadixComplexFFTTest.java Normal file
View File

@@ -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 <http://www.gnu.org/licenses/>
* ****************************************************************************
*/
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");
}
}

8
src/test/java/io/github/dsheirer/dsp/filter/channelizer/ComplexPolyphaseChannelizerM2Test.java
View File

@@ -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;