param.hpp

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// sbl/dsp/param.hpp — Float-domain parameter mapping utilities
//
// Standalone functions for normalizing inputs and mapping to parameter
// ranges with optional curve shaping. Complements scaled() on Pot and CvInput.
//
// Usage:
//   float t = sbl::dsp::math::cc_to_float(cc_value);       // 0-127 → [0, 1]
//   float cutoff = sbl::dsp::math::map_quadratic(t, 100.0f, 15000.0f);
 
#ifndef SBL_DSP_MATH_PARAM_HPP_
#define SBL_DSP_MATH_PARAM_HPP_
 
#include <cstdint>
#include <sbl/dsp/math/fast_math.hpp>
 
namespace sbl::dsp::math {
 
// ─── Normalize to [0.0, 1.0] ────────────────────────────────────
 
/// Normalize MIDI CC (0-127) to [0.0, 1.0]
inline constexpr float cc_to_float(uint8_t val) {
    return static_cast<float>(val) * (1.0f / 127.0f);
}
 
/// Normalize 16-bit unsigned (0-65535) to [0.0, 1.0]
inline constexpr float u16_to_float(uint16_t val) {
    return static_cast<float>(val) * (1.0f / 65535.0f);
}
 
/// Normalize 14-bit MIDI (0-16383) to [0.0, 1.0] (pitch bend, NRPN)
inline constexpr float u14_to_float(uint16_t val) {
    return static_cast<float>(val) * (1.0f / 16383.0f);
}
 
// ─── Map [0,1] → [min, max] with curve shaping ─────────────────
 
/// Linear mapping: t → min + (max - min) * t
inline constexpr float map_linear(float t, float min, float max) {
    return min + (max - min) * t;
}
 
/// Quadratic mapping: t² curve. Good for frequency, cutoff, LFO rate.
/// More resolution at low values, fast rise at high values.
inline constexpr float map_quadratic(float t, float min, float max) {
    return min + (max - min) * t * t;
}
 
/// S-curve mapping via Hermite smooth step: t²(3 - 2t).
/// Slow start, fast middle, slow finish. Good for crossfade morphs.
inline constexpr float map_scurve(float t, float min, float max) {
    float s = t * t * (3.0f - 2.0f * t);
    return min + (max - min) * s;
}
 
/// Inverse quadratic mapping: (2t - t²) curve. More resolution at high values.
/// Good for reverb decay, feedback — parameters where the interesting range
/// is near the maximum.
inline constexpr float map_inv_quadratic(float t, float min, float max) {
    float s = 2.0f * t - t * t;
    return min + (max - min) * s;
}
 
/// Exponential mapping: min * 2^(t * log2(max/min)).
/// Equal ratio per knob turn — the musically correct curve for time
/// parameters (attack, release, delay time) and frequency ranges.
/// Requires min > 0 and max > min.
inline float map_exponential(float t, float min, float max) {
    float octaves = __builtin_log2f(max / min);  // constant-folded when args are literals
    return min * fast_exp2f(t * octaves);
}
 
} // namespace sbl::dsp::math
 
#endif // SBL_DSP_MATH_PARAM_HPP_