Jungfraujoch/image_analysis/bragg_prediction/RotationColumnRange.h

// SPDX-FileCopyrightText: 2026 Filip Leonarski, Paul Scherrer Institute <filip.leonarski@psi.ch>
// SPDX-License-Identifier: GPL-3.0-only

#pragma once

// Which l of an (h, k) column a rotation predictor needs to walk, shared by the CPU and the GPU predictor
// (BraggPredictionRot.cpp explains the bound) so that both walk the same l.

#include <cmath>

#include "../../common/JFJochMath.h"

#ifdef __CUDACC__
#define ROTATION_COLUMN_HD __host__ __device__ inline
#else
#define ROTATION_COLUMN_HD inline
#endif

// The largest |phi| at which a solution can still pass the rocking-curve test: a solution further from
// the frame has zeta (|phi| - half wedge) above the test's limit for every zeta >= min_zeta, the rocking
// width being largest at the resolution limit. With a 1e-3 rad margin, far above float rounding.
// -1 = nothing is bounded (no min_zeta, or a bound past pi).
ROTATION_COLUMN_HD double RotationPhiLimit(float min_zeta, float mos_angle_rad, float bandwidth_sigma,
                                           float half_wavelength_A, float one_over_dmax,
                                           float half_wedge_angle_rad, float mosaicity_multiplier) {
    if (!(min_zeta > 0.0f))
        return -1.0;
    double mos_max_rad = mos_angle_rad;
    if (bandwidth_sigma > 0.0f) {
        const double sin_theta = half_wavelength_A * static_cast<double>(one_over_dmax);
        const double dphi_bw = sin_theta < 1.0
                               ? bandwidth_sigma * sin_theta / sqrt(1.0 - sin_theta * sin_theta)
                               : INFINITY;
        mos_max_rad = sqrt(mos_max_rad * mos_max_rad + dphi_bw * dphi_bw);
    }
    const double phi_limit = half_wedge_angle_rad + (mosaicity_multiplier * mos_max_rad + 1e-5) / min_zeta + 1e-3;
    return phi_limit < PI ? phi_limit : -1.0;
}

// The l of a column to walk: f(l) = C_C l^2 + b l + c <= f_max on [l_lo, l_hi], and f(l) < -f_max strictly
// inside (skip_lo, skip_hi), which may be empty. False where no l of the column can pass. inv_2C_C is
// 1 / (2 C_C): a product rather than four divisions, which on a GPU are each a sequence of double
// operations; the whole-index widening of each end covers the difference in rounding.
struct RotationColumn {
    int l_lo, l_hi, skip_lo, skip_hi;
};

ROTATION_COLUMN_HD bool RotationColumnRange(double C_C, double inv_2C_C, double b, double c, double f_max,
                                            int max_l, RotationColumn &col) {
    // A root of the quadratic as an index, held inside the box first so the conversion cannot overflow.
    const auto to_l = [max_l](double v) {
        const double lo = -max_l - 2.0, hi = max_l + 2.0;
        return static_cast<int>(v < lo ? lo : (v > hi ? hi : v));
    };
    col = {-max_l, max_l, max_l + 1, max_l + 1};
    const double disc_hi = b * b - 4.0 * C_C * (c - f_max);
    if (!(disc_hi >= 0.0))
        return false;
    const double r_hi = sqrt(disc_hi);
    const int lo = to_l(ceil((-b - r_hi) * inv_2C_C)) - 1;
    const int hi = to_l(floor((-b + r_hi) * inv_2C_C)) + 1;
    col.l_lo = lo > col.l_lo ? lo : col.l_lo;
    col.l_hi = hi < col.l_hi ? hi : col.l_hi;
    const double disc_lo = b * b - 4.0 * C_C * (c + f_max);
    if (disc_lo > 0.0) {
        const double r_lo = sqrt(disc_lo);
        col.skip_lo = to_l(floor((-b - r_lo) * inv_2C_C)) + 2;
        col.skip_hi = to_l(ceil((-b + r_lo) * inv_2C_C)) - 2;
    }
    return true;
}