warp.hpp

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// sbl/dsp/warp.hpp — Float warp engines for envelope/parameter shaping
//
// Float-domain warp engines for the Audio stack (SegmentGenerator).
// Phase and curve are both float; no LUT or fixed-point math required.
//
// Phase: [0.0, 1.0] — linear ramp through the segment
// Curve: [-1.0, 1.0] where:
//   -1.0 = full concave (fast start, slow approach to target)
//    0.0 = linear (no shaping)
//    1.0 = full convex (slow start, fast snap to target)
//
// See FDP-016 for design rationale.
 
#ifndef SBL_DSP_PRIMITIVES_WARP_HPP_
#define SBL_DSP_PRIMITIVES_WARP_HPP_
 
namespace sbl::dsp::primitives {
 
/// Rational function warp (float). Zero flash, zero RAM.
/// f(t) = (1+a)*t / (1+a*t), with a = K * curve^2.
/// Inspired by MI Stages WarpPhase (MIT).
struct FloatRationalWarp {
    static constexpr float K = 128.0f;
 
    /// @note ISR-safe — bounded computation, no I/O.
    static float warp(float phase, float curve) {
        if (curve > -0.001f && curve < 0.001f) return phase;
 
        bool flip = curve > 0.0f;
        float t = flip ? (1.0f - phase) : phase;
        float dc = flip ? curve : -curve;
 
        float a = K * dc * dc;
        float num = (1.0f + a) * t;
        float den = 1.0f + a * t;
        float result = num / den;
 
        if (result > 1.0f) result = 1.0f;
        return flip ? (1.0f - result) : result;
    }
};
 
/// Default float warp engine for SegmentGenerator.
/// FloatRationalWarp: zero flash, analytical, good character.
using FloatDefaultWarp = FloatRationalWarp;
 
} // namespace sbl::dsp::primitives
 
#endif // SBL_DSP_PRIMITIVES_WARP_HPP_