Непредсказуемые изменения точности расчётов внутри kernel

#include <QCoreApplication>
#include <QDebug>
#include <QFile>
#include <QtMath>
#include <CL/cl.hpp>
 
double distanceD(double point1[2], double point2[2])
{
    double R = 6371110.0;
    double phi1 = point1[0];
    double lambda1 = point1[1];
 
    double phi2 = point2[0];
    double lambda2 = point2[1];
 
    double delta_lambda = lambda2 - lambda1;
 
    double p1 = sin(delta_lambda) * cos(phi2);
    double p2 = cos(phi1) * sin(phi2) - sin(phi1) * cos(phi2) * cos(delta_lambda);
    double q = sin(phi1) * sin(phi2) + cos(phi1) * cos(phi2) * cos(delta_lambda);
    double res = abs(atan2(sqrt(p1 * p1 + p2 * p2), q) * R);
 
    qDebug() << Qt::scientific << qSetRealNumberPrecision(18) << "CPU p2      =" << p2;
    qDebug() << Qt::scientific << qSetRealNumberPrecision(18) << "CPU res     =" << res;
 
    double p2_h1 = cos(phi1) * sin(phi2);
    double p2_h2 = sin(phi1) * cos(phi2) * cos(delta_lambda);
    double p2_sum = p2_h1 - p2_h2;
 
    qDebug() << Qt::scientific << qSetRealNumberPrecision(18) << "CPU p2_h1   =" << p2_h1 ;
    qDebug() << Qt::scientific << qSetRealNumberPrecision(18) << "CPU p2_h2   =" << p2_h2 ;
    qDebug() << Qt::scientific << qSetRealNumberPrecision(18) << "CPU p2_sum  =" << p2_sum;
 
    return res;
}
 
 
int main(int argc, char *argv[])
{
    std::vector<cl::Platform> all_platforms;
    cl::Platform::get(&all_platforms);
    if(all_platforms.size() == 0){
        qDebug() << "No platforms found. Check OpenCL installation.";
        return 1;
    }
    cl::Platform default_platform=all_platforms[0];
    qDebug() << "Using platform: " << QString::fromStdString(default_platform.getInfo<CL_PLATFORM_NAME>());
 
    std::vector<cl::Device> all_devices;
    default_platform.getDevices(CL_DEVICE_TYPE_ALL, &all_devices);
    if(all_devices.size() == 0){
        qDebug() << "No devices found. Check OpenCL installation or make sure at least one compatible GPU is connected.";
        return 1;
    }
    cl::Device default_device=all_devices[0];
    qDebug() << "Using device: " << QString::fromStdString(default_device.getInfo<CL_DEVICE_NAME>());
 
    qDebug() << "Using CL version: " << QString::fromStdString(default_device.getInfo<CL_DEVICE_VERSION>());
 
    cl::Context context(default_device);
 
    cl::Program::Sources sources;
 
    QFile kernelCode1(":/CalcDist.cl");
    kernelCode1.open(QFile::ReadOnly | QFile::Text);
    std::string codeString = kernelCode1.readAll().toStdString();
    unsigned long long codeStringSize = codeString.length();
 
    sources.push_back({codeString.c_str(), codeStringSize});
 
    cl::Program program(context,sources);
    if(program.build({default_device})!=CL_SUCCESS){
        qDebug() << " Error building: " << QString::fromStdString(program.getBuildInfo<CL_PROGRAM_BUILD_LOG>(default_device));
        return 1;
    }
 
    cl::CommandQueue queue(context,default_device);
 
    cl::compatibility::make_kernel<> calcDist(cl::Kernel(program, "mainProgram"));
    cl::EnqueueArgs eargs(queue, cl::NullRange, cl::NDRange(1), cl::NullRange);
 
    calcDist(eargs).wait();
 
    double p1  [2] = {0.891949793450334649, 0.513485940430910115};
    double p2  [2] = {0.891949846176460226, 0.513485940430959964};
 
    double dist = distanceD(p1, p2);
    qDebug() << Qt::scientific << qSetRealNumberPrecision(18) << "CPU dist    =" << dist;
 
    return 0;
}