Method getFFT

src/fl/audio/audio_context.cpp.hpp:35–92

Context::~Context() FL_NOEXCEPT = default;

shared_ptr<const fft::Bins> Context::getFFT(int bands, float fmin, float fmax, fft::Mode mode, fft::Window window) {
    fft::Args args(mSample.size(), bands, fmin, fmax, mSampleRate, mode, window);

    // O(1) cache lookup using hash map
    fl::size argsHash = hashFFTArgs(args);
    auto it = mFFTCacheMap.find(argsHash);
    if (it != mFFTCacheMap.end()) {
        int idx = it->second;
        if (idx >= 0 && idx < static_cast<int>(mFFTCache.size())) {
            // Double-check args match in case of hash collision
            if (mFFTCache[idx].args == args) {
                return mFFTCache[idx].bins;
            }
        }
    }

    // Not cached — try to recycle a previously-used fft::Bins with matching band count
    shared_ptr<fft::Bins> bins;
    for (size i = 0; i < mRecyclePool.size(); i++) {
        if (static_cast<int>(mRecyclePool[i]->bands()) == bands) {
            bins = fl::move(mRecyclePool[i]);
            mRecyclePool.erase(mRecyclePool.begin() + i);
            bins->clear(); // Vectors keep capacity — zero allocs
            break;
        }
    }
    if (!bins) {
        bins = fl::make_shared<fft::Bins>(bands);
    }

    fl::span<const fl::i16> sample = mSample.pcm();
    mFFT.run(sample, bins.get(), args);

    // Evict oldest if at capacity
    if (static_cast<int>(mFFTCache.size()) >= MAX_FFT_CACHE_ENTRIES) {
        // Remove the oldest entry's hash from hash map
        fl::size oldHash = hashFFTArgs(mFFTCache[0].args);
        mFFTCacheMap.erase(oldHash);

        // Shift all remaining entries and update map indices
        for (size i = 1; i < mFFTCache.size(); i++) {
            fl::size key = hashFFTArgs(mFFTCache[i].args);
            mFFTCacheMap[key] = static_cast<int>(i - 1);
        }
        mFFTCache.erase(mFFTCache.begin());
    }

    FFTCacheEntry entry;
    entry.args = args;
    entry.bins = bins;
    int newIndex = static_cast<int>(mFFTCache.size());
    mFFTCache.push_back(fl::move(entry));

    // Add to hash map for O(1) future lookups
    mFFTCacheMap[argsHash] = newIndex;

    return bins;
}