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Wrap FFTPACK with PRIK

Build the bundled modern fortran-lang/fftpack source with PRIK and validate all 31 public procedures in its fftpack module against NumPy, SciPy, or explicit transform invariants.

No f2py comparison wrapper is used: independent mathematical results are the primary oracle. The inventory has no unsupported or skipped procedures.

Requirements

Install GNU Fortran. On Ubuntu:

sudo apt-get update
sudo apt-get install --yes gfortran

Install the pinned numerical tools:

python3 -m pip install "numpy==2.5.1" "scipy==1.18.0" pytest

Run the remaining commands from the PRIK repository root.

Quick start

Build the extension and run the complete test suite:

source examples/fftpack/build_all.sh
python3 -m pytest -q examples/fftpack/tests

Use source so the build directory exported by build_all.sh remains on PYTHONPATH for pytest.

How the build works

fftpack.f90 is the authoritative API. rk.f90 supplies its kind parameter, and fftpack_*.f90 supplies its submodule implementations. The remaining legacy kernels are compiled through --native-fortran-sources, so they satisfy native dependencies without contributing storage-level signatures to the Python API.

Every source is compiled once and no alternative wrapper is created.

Build the PRIK wrapper

export EXAMPLE_WORKSPACE="$PWD"
export FFTPACK_BUILD_ROOT="$(mktemp -d)"
export FFTPACK_NATIVE_DIR="$EXAMPLE_WORKSPACE/examples/fftpack/native"

FFTPACK_PUBLIC_SOURCES=(
  "$FFTPACK_NATIVE_DIR/rk.f90"
  "$FFTPACK_NATIVE_DIR/fftpack.f90"
  "$FFTPACK_NATIVE_DIR"/fftpack_*.f90
)
FFTPACK_LINK_ONLY_SOURCES=()
for source in "$FFTPACK_NATIVE_DIR"/*.f90; do
  case "${source##*/}" in
    rk.f90|fftpack.f90|fftpack_*.f90) continue ;;
  esac
  FFTPACK_LINK_ONLY_SOURCES+=("$source")
done

mkdir -p "$FFTPACK_BUILD_ROOT/prik/generated"
cd "$FFTPACK_BUILD_ROOT/prik"

python3 -m prik "${FFTPACK_PUBLIC_SOURCES[@]}" \
  --native-fortran-sources "${FFTPACK_LINK_ONLY_SOURCES[@]}" \
  --out prik_reference_fftpack \
  --out-dir "$FFTPACK_BUILD_ROOT/prik/generated" \
  --compiler "$(command -v gfortran)" \
  --jobs 8 \
  --wrapper-fortran-flags="-O0 -g0" \
  --wrapper-c-flags="-O0 -g0"

Run focused tests

After the quick-start build, run one procedure or family:

python3 -m pytest -q examples/fftpack/tests/test_transforms.py
python3 -m pytest -q \
  examples/fftpack/tests/test_transforms.py::test_zfftf
python3 -m pytest -q examples/fftpack/tests -k dct

What is validated

The suite covers all 31 public work-array, FFT, DCT, frequency, and shift procedures. NumPy is the oracle for Fourier transforms, shifts, and frequency ordering; SciPy is the oracle for cosine and sine families. The tests verify normalization, in-place mutation, high-level input preservation, dtype, shape, and allocatable-result cleanup.

The public routine list stays in sync with the generated exports, and every public procedure is exercised.

Sources and license

The .f90 files under native/ match the upstream src/ files at fortran-lang/fftpack commit 0fffe7c05a918363a7cc12ae138a695afd115f36. See the upstream repository, API documentation, and license before redistributing the bundled native sources.