folder.hpp

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// sbl/dsp/folder.hpp — Wavefold primitive
//
// Reflects a signal at ±1.0 boundaries via triangle-wave reflection.
// The mathematical fold operation, without antialiasing.
//
// For production real-time audio, prefer WavefoldAA (dsp/wavefold.hpp)
// which eliminates aliasing via second-order ADAA.
//
// Usage:
//   sbl::dsp::Folder folder;
//   float out = folder.process(in * depth);
 
#ifndef SBL_DSP_PRIMITIVES_FOLDER_HPP_
#define SBL_DSP_PRIMITIVES_FOLDER_HPP_
 
#include <cmath>
#include <cstdint>
 
namespace sbl::dsp::primitives {
 
class Folder {
public:
    /// Process a single sample — fold x into [-1, 1] via triangle-wave reflection
    float process(float x) { return fold(x); }
 
    /// Process a block in-place
    void process(float* buf, uint16_t frames) {
        for (uint16_t i = 0; i < frames; ++i) {
            buf[i] = fold(buf[i]);
        }
    }
 
    /// The fold function, available for math use (e.g., WavefoldAA antiderivatives)
    static float fold(float x) {
        const float p = x + 1.0f;
        const float q = p - 4.0f * floorf(p * 0.25f);  // mod 4, range [0, 4)
        return (q < 2.0f) ? (q - 1.0f) : (3.0f - q);
    }
};
 
} // namespace sbl::dsp::primitives
 
#endif // SBL_DSP_PRIMITIVES_FOLDER_HPP_