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Merge pull request #19583 from theroyalpekka:patch-1

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* Update polynom_solver.cpp

This pull request is in the response to Issue  #19526. I have fixed the problem with the cube root calculation of 2*R. The Issue was in the usage of pow function with negative values of R, but if it is calculated for only positive values of R then changing x0 according to the parity of R, the Issue is resolved. Kindly consider it, Thanks!

* add cv::cubeRoot(double)

Co-authored-by: Alexander Alekhin <alexander.a.alekhin@gmail.com>
This commit is contained in:
Mradul Agrawal 2021-03-05 19:25:52 +05:30 committed by GitHub
parent a1e2c4f338
commit 640f188ca2
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2 changed files with 26 additions and 3 deletions
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14
modules/calib3d/src/polynom_solver.cpp
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@ -65,7 +65,8 @@ int solve_deg3(double a, double b, double c, double d,
return 3; return 3;
} }
else { else {
x0 = pow(2 * R, 1 / 3.0) - b_a_3; double cube_root = cv::cubeRoot(2 * R);
x0 = cube_root - b_a_3;
return 1; return 1;
} }
} }
@ -82,8 +83,15 @@ int solve_deg3(double a, double b, double c, double d,
} }
// D > 0, only one real root // D > 0, only one real root
double AD = pow(fabs(R) + sqrt(D), 1.0 / 3.0) * (R > 0 ? 1 : (R < 0 ? -1 : 0)); double AD = 0.;
double BD = (AD == 0) ? 0 : -Q / AD; double BD = 0.;
double R_abs = fabs(R);
if (R_abs > DBL_EPSILON)
{
AD = cv::cubeRoot(R_abs + sqrt(D));
AD = (R >= 0) ? AD : -AD;
BD = -Q / AD;
}
// Calculate the only real root // Calculate the only real root
x0 = AD + BD - b_a_3; x0 = AD + BD - b_a_3;

15
modules/core/include/opencv2/core/base.hpp
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@ -587,6 +587,21 @@ _AccTp normInf(const _Tp* a, const _Tp* b, int n)
*/ */
CV_EXPORTS_W float cubeRoot(float val); CV_EXPORTS_W float cubeRoot(float val);
/** @overload
cubeRoot with argument of `double` type calls `std::cbrt(double)` (C++11) or falls back on `pow()` for C++98 compilation mode.
*/
static inline
double cubeRoot(double val)
{
#ifdef CV_CXX11
return std::cbrt(val);
#else
double v = pow(abs(val), 1/3.); // pow doesn't support negative inputs with fractional exponents
return val >= 0 ? v : -v;
#endif
}
/** @brief Calculates the angle of a 2D vector in degrees. /** @brief Calculates the angle of a 2D vector in degrees.
The function fastAtan2 calculates the full-range angle of an input 2D vector. The angle is measured The function fastAtan2 calculates the full-range angle of an input 2D vector. The angle is measured