blep.hpp

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#pragma once

 
#include <cmath>
 
namespace pulp::signal::osc {

inline constexpr double kNoDiscontinuity = -1.0;

struct Correction {
    double before = 0.0;
    double after = 0.0;
};

inline double blep_residual(double x) noexcept {
    if (x < -1.0 || x >= 1.0) return 0.0;
    if (x < 0.0) return 0.5 * x * x + x + 0.5;
    return x - 0.5 * x * x - 0.5;
}

inline double blamp_residual(double x) noexcept {
    if (x < -1.0 || x >= 1.0) return 0.0;
    if (x < 0.0) return x * x * x / 6.0 + 0.5 * x * x + 0.5 * x + 1.0 / 6.0;
    return 0.5 * x * x - x * x * x / 6.0 - 0.5 * x + 1.0 / 6.0;
}

inline Correction poly_blep(double d, double height) noexcept {
    if (!(d >= 0.0 && d <= 1.0)) return {0.0, 0.0};
    // Before tap at x = -d, always in [-1, 0]: the pre-step branch, which is
    // `0.5x^2 + x + 0.5` rewritten in d.
    const double before = 0.5 * d * d - d + 0.5;
    // After tap at x = 1 - d, always in [0, 1]: the post-step branch.
    const double x = 1.0 - d;
    const double after = x - 0.5 * x * x - 0.5;
    return {height * before, height * after};
}

inline Correction poly_blamp(double d, double slope_change) noexcept {
    if (!(d >= 0.0 && d <= 1.0)) return {0.0, 0.0};
    return {slope_change * blamp_residual(-d), slope_change * blamp_residual(1.0 - d)};
}

inline double wrap_position(double phase_after, double increment) noexcept {
    if (!(increment > 0.0)) return kNoDiscontinuity;
    const double d = 1.0 - phase_after / increment;
    return std::isfinite(d) ? d : kNoDiscontinuity;
}
 
} // namespace pulp::signal::osc