waveshaper.hpp

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// sbl/dsp/waveshaper.hpp — Table-driven waveshaping / transfer function
//
// Maps input samples through a lookup table for distortion, saturation,
// or other nonlinear transfer functions. Input range [-1.0, 1.0] maps
// to the full table.
//
// Usage:
//   sbl::dsp::Waveshaper<256> shaper;
//   shaper.set_table(my_transfer_table);
//   float out = shaper.process(in);
 
#pragma once
 
#include <cstdint>
 
#include <sbl/dsp/lut.hpp>
 
namespace sbl::dsp {
 
template<uint16_t Size>
class Waveshaper {
public:
    /// @note All public methods are ISR-safe — bounded computation, no I/O.
 
    /** @brief Set the transfer function table (Size+1 entries with guard) */
    void set_table(const float* table) { table_ = table; }
 
    /**
     * @brief Process a single sample through the transfer function
     *
     * Input [-1.0, 1.0] maps to full table range.
     * Values outside this range are clamped.
     */
    float process(float x) const {
        // Clamp to [-1.0, 1.0]
        if (x > 1.0f) x = 1.0f;
        if (x < -1.0f) x = -1.0f;
 
        // Map [-1.0, 1.0] to uint32_t phase [0, 2^32)
        // -1.0 → 0x00000000, 0.0 → 0x80000000, 1.0 → 0xFFFFFF00
        float norm = x * 0.5f + 0.5f;  // [0.0, 1.0]
        uint32_t phase = static_cast<uint32_t>(norm * 4294967040.0f);  // 0xFFFFFF00 avoids float→uint32 overflow
 
        return lut::lookup_linear<Size>(table_, phase);
    }
 
    /**
     * @brief Process a block of samples in-place
     */
    void process(float* buf, uint16_t frames) const {
        for (uint16_t i = 0; i < frames; ++i) {
            buf[i] = process(buf[i]);
        }
    }
 
private:
    const float* table_ = nullptr;
};
 
} // namespace sbl::dsp