Tools.h

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#ifndef JIXIE_SVD_TOOLS_H
#define JIXIE_SVD_TOOLS_H
 
#pragma GCC diagnostic push
#pragma GCC diagnostic ignored "-Wdeprecated-declarations"
#include <Eigen/Dense>
#include <Eigen/Core>
#include <Eigen/SVD>
#pragma GCC diagnostic pop
 
#if !defined(__APPLE__) || defined(__i386__) || defined(__x86_64__)
#include <mmintrin.h>
#include <xmmintrin.h>
#endif
#include <cmath>
#include <random>
#include <chrono>
#include <iostream>
#include <iomanip>
 
namespace JIXIE {
 
template <bool B, class T = void>
using enable_if_t = typename std::enable_if<B, T>::type;
 
namespace MATH_TOOLS {
 
inline float approx_rsqrt(float a)
{
    // return 1.0f / std::sqrt(a);
#if !defined(__APPLE__) || defined(__i386__) || defined(__x86_64__)
    return _mm_cvtss_f32(_mm_rsqrt_ss(_mm_set_ss(a)));
#else
    return vgetq_lane_f32(vrsqrteq_f32(vld1q_dup_f32(&a)), 0);
#endif
}
 
inline float rsqrt(float a)
{
    return (float)1.0f / std::sqrt(a);
 
    // float b = approx_rsqrt(a);
    // // Newton step with f(x) = a - 1/x^2
    // b = 0.5f * b * (3.0f - a * (b * b));
    // return b;
}
 
inline double rsqrt(double a)
{
    using std::sqrt;
    return 1 / sqrt(a);
}
} // namespace MATH_TOOLS
 
namespace INTERNAL {
using namespace std;
template <class T, class Enable = void>
struct ScalarTypeHelper {
    using type = typename T::Scalar;
};
template <class T>
struct ScalarTypeHelper<T, enable_if_t<is_arithmetic<T>::value>> {
    using type = T;
};
} // namespace INTERNAL
 
template <class T>
using ScalarType = typename INTERNAL::ScalarTypeHelper<T>::type;
 
template <class MatrixType>
constexpr bool isSize(int m, int n)
{
    return MatrixType::RowsAtCompileTime == m && MatrixType::ColsAtCompileTime == n;
}
 
} // namespace JIXIE
#endif