zufft bundles the FFT component of ducc0 ("Distinctly Useful Code
Collection"), https://gitlab.mpcdf.mpg.de/mtr/ducc, in src/ducc0/.

The bundled files are exactly the subset SciPy vendors in
subprojects/duccfft: the files of ducc0 whose SPDX line reads
"BSD-3-Clause OR GPL-2.0-or-later". zufft elects the BSD-3-Clause licence
for them. The rest of ducc0 is GPL-2.0-or-later only and is not included.
tools/vendor/manifest.tsv records the ducc0 and SciPy commits, and
tools/vendor/checksums.sha256 the SHA-256 of every bundled file, in the
package's source repository.

Copyright holders named in the bundled files:

  Copyright (C) 2002-2026 Max-Planck-Society
  Copyright (C) 2019-2023 Peter Bell
  Authors: Martin Reinecke, Peter Bell

src/ducc0/fft/fft1d_impl.h, for the odd-sized DCT-IV transforms:

  Copyright (C) 2003, 2007-14 Matteo Frigo
  Copyright (C) 2003, 2007-14 Massachusetts Institute of Technology

  These notices sit above the same dual "BSD-3-Clause OR GPL-2.0-or-later"
  SPDX line as the rest of the file.

src/ducc0/infra/threading.cc, two helper templates (a y-combinator) inside
a block that is compiled only when DUCC0_HIERARCHICAL_SUBMISSION is
defined, which zufft never does:

  Copyright 2015 The TensorFlow Authors.

The functions prev_good_size_cmplx() and prev_good_size_real() in
src/zff_lengths.cpp are ported from SciPy's
scipy/fft/_duccfft/pyduccfft.cxx, part of SciPy's duccfft, which is
licensed under the 3-clause BSD licence below ("Licensed under a 3-clause
BSD style license - see LICENSE.md"). Copyright SciPy Developers.

The BSD-3-Clause licence of the bundled files (src/ducc0/LICENSE.md):

Copyright (C) 2010-2019 Max-Planck-Society
All rights reserved.

Redistribution and use in source and binary forms, with or without modification,
are permitted provided that the following conditions are met:

* Redistributions of source code must retain the above copyright notice, this
  list of conditions and the following disclaimer.
* 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.
* Neither the name of the copyright holder 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 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 HOLDER 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.