omath/source/projectile_prediction/ProjPredEngineAVX2.cpp

//
// Created by Vlad on 2/23/2025.
//
#include "omath/projectile_prediction/ProjPredEngineAVX2.hpp"
#include "source_location"

namespace omath::projectile_prediction
{
    std::optional<Vector3<float>>
    ProjPredEngineAVX2::MaybeCalculateAimPoint([[maybe_unused]] const Projectile& projectile,
                                               [[maybe_unused]] const Target& target) const
    {
#ifdef OMATH_USE_AVX2
        const float bulletGravity = m_gravityConstant * projectile.m_gravityScale;
        const float v0 = projectile.m_launchSpeed;
        const float v0Sqr = v0 * v0;
        const Vector3 projOrigin = projectile.m_origin;

        constexpr int SIMD_FACTOR = 8;
        float currentTime = m_simulationTimeStep;

        for (; currentTime <= m_maximumSimulationTime; currentTime += m_simulationTimeStep * SIMD_FACTOR)
        {
            const __m256 times =
                    _mm256_setr_ps(currentTime, currentTime + m_simulationTimeStep,
                                   currentTime + m_simulationTimeStep * 2, currentTime + m_simulationTimeStep * 3,
                                   currentTime + m_simulationTimeStep * 4, currentTime + m_simulationTimeStep * 5,
                                   currentTime + m_simulationTimeStep * 6, currentTime + m_simulationTimeStep * 7);

            const __m256 targetX =
                    _mm256_fmadd_ps(_mm256_set1_ps(target.m_velocity.x), times, _mm256_set1_ps(target.m_origin.x));
            const __m256 targetY =
                    _mm256_fmadd_ps(_mm256_set1_ps(target.m_velocity.y), times, _mm256_set1_ps(target.m_origin.y));
            const __m256 timesSq = _mm256_mul_ps(times, times);
            const __m256 targetZ = _mm256_fmadd_ps(_mm256_set1_ps(target.m_velocity.z), times,
                                                   _mm256_fnmadd_ps(_mm256_set1_ps(0.5f * m_gravityConstant), timesSq,
                                                                    _mm256_set1_ps(target.m_origin.z)));

            const __m256 deltaX = _mm256_sub_ps(targetX, _mm256_set1_ps(projOrigin.x));
            const __m256 deltaY = _mm256_sub_ps(targetY, _mm256_set1_ps(projOrigin.y));
            const __m256 deltaZ = _mm256_sub_ps(targetZ, _mm256_set1_ps(projOrigin.z));

            const __m256 dSqr = _mm256_add_ps(_mm256_mul_ps(deltaX, deltaX), _mm256_mul_ps(deltaY, deltaY));

            const __m256 bgTimesSq = _mm256_mul_ps(_mm256_set1_ps(bulletGravity), timesSq);
            const __m256 term = _mm256_add_ps(deltaZ, _mm256_mul_ps(_mm256_set1_ps(0.5f), bgTimesSq));
            const __m256 termSq = _mm256_mul_ps(term, term);
            const __m256 numerator = _mm256_add_ps(dSqr, termSq);
            const __m256 denominator = _mm256_add_ps(timesSq, _mm256_set1_ps(1e-8f)); // Avoid division by zero
            const __m256 requiredV0Sqr = _mm256_div_ps(numerator, denominator);

            const __m256 v0SqrVec = _mm256_set1_ps(v0Sqr + 1e-3f);
            const __m256 mask = _mm256_cmp_ps(requiredV0Sqr, v0SqrVec, _CMP_LE_OQ);

            const unsigned validMask = _mm256_movemask_ps(mask);

            if (!validMask)
                continue;

            alignas(32) float validTimes[SIMD_FACTOR];
            _mm256_store_ps(validTimes, times);

            for (int i = 0; i < SIMD_FACTOR; ++i)
            {
                if (!(validMask & (1 << i)))
                    continue;

                const float candidateTime = validTimes[i];

                if (candidateTime > m_maximumSimulationTime)
                    continue;

                // Fine search around candidate time
                for (float fineTime = candidateTime - m_simulationTimeStep * 2;
                     fineTime <= candidateTime + m_simulationTimeStep * 2; fineTime += m_simulationTimeStep)
                {
                    if (fineTime < 0)
                        continue;

                    const Vector3 targetPos = target.PredictPosition(fineTime, m_gravityConstant);
                    const auto pitch = CalculatePitch(projOrigin, targetPos, bulletGravity, v0, fineTime);
                    if (!pitch)
                        continue;

                    const Vector3 delta = targetPos - projOrigin;
                    const float d = std::sqrt(delta.x * delta.x + delta.y * delta.y);
                    const float height = d * std::tan(angles::DegreesToRadians(*pitch));
                    return Vector3(targetPos.x, targetPos.y, projOrigin.z + height);
                }
            }
        }

        // Fallback scalar processing for remaining times
        for (; currentTime <= m_maximumSimulationTime; currentTime += m_simulationTimeStep)
        {
            const Vector3 targetPos = target.PredictPosition(currentTime, m_gravityConstant);
            const auto pitch = CalculatePitch(projOrigin, targetPos, bulletGravity, v0, currentTime);
            if (!pitch)
                continue;

            const Vector3 delta = targetPos - projOrigin;
            const float d = std::sqrt(delta.x * delta.x + delta.y * delta.y);
            const float height = d * std::tan(angles::DegreesToRadians(*pitch));
            return Vector3(targetPos.x, targetPos.y, projOrigin.z + height);
        }

        return std::nullopt;
    }
    ProjPredEngineAVX2::ProjPredEngineAVX2(const float gravityConstant, const float simulationTimeStep,
                                           const float maximumSimulationTime) :
        m_gravityConstant(gravityConstant), m_simulationTimeStep(maximumSimulationTime),
        m_maximumSimulationTime(simulationTimeStep)
    {
    }
    std::optional<float> ProjPredEngineAVX2::CalculatePitch(const Vector3<float>& projOrigin,
                                                            const Vector3<float>& targetPos, const float bulletGravity,
                                                            const float v0, const float time)
    {
        if (time <= 0.0f)
            return std::nullopt;

        const Vector3 delta = targetPos - projOrigin;
        const float dSqr = delta.x * delta.x + delta.y * delta.y;
        const float h = delta.z;

        const float term = h + 0.5f * bulletGravity * time * time;
        const float requiredV0Sqr = (dSqr + term * term) / (time * time);
        const float v0Sqr = v0 * v0;

        if (requiredV0Sqr > v0Sqr + 1e-3f)
            return std::nullopt;

        if (dSqr == 0.0f)
            return term >= 0.0f ? 90.0f : -90.0f;


        const float d = std::sqrt(dSqr);
        const float tanTheta = term / d;
        return angles::RadiansToDegrees(std::atan(tanTheta));
#else
        throw std::runtime_error(
                std::format("{} AVX2 feature is not enabled!", std::source_location::current().function_name()));
#endif
    }
} // namespace omath::projectile_prediction