libgromacs-dev 2018.1-1 / usr / include / gromacs / math / utilities.h

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#ifndef GMX_MATH_UTILITIES_H
#define GMX_MATH_UTILITIES_H

#include <limits.h>

#include <cmath>

#include "gromacs/utility/basedefinitions.h"
#include "gromacs/utility/real.h"

#ifdef __cplusplus
extern "C" {
#endif

#ifndef M_PI
#define M_PI        3.14159265358979323846
#endif

#ifndef M_PI_2
#define M_PI_2      1.57079632679489661923
#endif

#ifndef M_2PI
#define M_2PI       6.28318530717958647692
#endif

#ifndef M_SQRT2
#define M_SQRT2 sqrt(2.0)
#endif

#ifndef M_1_PI
#define M_1_PI      0.31830988618379067154
#endif

#ifndef M_FLOAT_1_SQRTPI /* used in GPU kernels */
/* 1.0 / sqrt(M_PI) */
#define M_FLOAT_1_SQRTPI 0.564189583547756f
#endif

#ifndef M_1_SQRTPI
/* 1.0 / sqrt(M_PI) */
#define M_1_SQRTPI 0.564189583547756
#endif

#ifndef M_2_SQRTPI
/* 2.0 / sqrt(M_PI) */
#define M_2_SQRTPI  1.128379167095513
#endif

/*! \brief Enum to select safe or highly unsafe (faster) math functions.
 *
 *  Normally all the Gromacs math functions should apply reasonable care with
 *  input arguments. While we do not necessarily adhere strictly to IEEE
 *  (in particular not for arguments that might result in NaN, inf, etc.), the
 *  functions should return reasonable values or e.g. clamp results to zero.
 *
 *  However, in a few cases where we are extremely performance-sensitive it
 *  makes sense to forego these checks too in cases where we know the exact
 *  properties if the input data, and we really need to save every cycle we can.
 *
 *  This class is typically used as a template parameter to such calls to enable
 *  the caller to select the level of aggressiveness. We should always use the
 *  safe alternative as the default value, and document carefully what might
 *  happen with the unsafe alternative.
 */
enum class MathOptimization
{
    Safe,    //!< Don't do unsafe optimizations. This should always be default.
    Unsafe   //!< Allow optimizations that can be VERY dangerous for general code.
};

/*! \brief Check if two numbers are within a tolerance
 *
 *  This routine checks if the relative difference between two numbers is
 *  approximately within the given tolerance, defined as
 *  fabs(f1-f2)<=tolerance*fabs(f1+f2).
 *
 *  To check if two floating-point numbers are almost identical, use this routine
 *  with the tolerance GMX_REAL_EPS, or GMX_DOUBLE_EPS if the check should be
 *  done in double regardless of Gromacs precision.
 *
 *  To check if two algorithms produce similar results you will normally need
 *  to relax the tolerance significantly since many operations (e.g. summation)
 *  accumulate floating point errors.
 *
 *  \param f1  First number to compare
 *  \param f2  Second number to compare
 *  \param tol Tolerance to use
 *
 *  \return 1 if the relative difference is within tolerance, 0 if not.
 */
int
gmx_within_tol(double   f1,
               double   f2,
               double   tol);

/*!
 * \brief Check if a number is smaller than some preset safe minimum
 * value, currently defined as GMX_REAL_MIN/GMX_REAL_EPS.
 *
 * If a number is smaller than this value we risk numerical overflow
 * if any number larger than 1.0/GMX_REAL_EPS is divided by it.
 *
 * \return 1  if 'almost' numerically zero, 0 otherwise.
 */
int
gmx_numzero(double a);

/*! \brief Multiply two large ints
 *
 * \return False iff overflow occurred
 */
gmx_bool
check_int_multiply_for_overflow(gmx_int64_t  a,
                                gmx_int64_t  b,
                                gmx_int64_t *result);

/*! \brief Find greatest common divisor of two numbers
 *
 * \return GCD of the two inputs
 */
int
gmx_greatest_common_divisor(int p, int q);


/*! \brief Enable floating-point exceptions if supported on OS
 *
 * Enables division-by-zero, invalid, and overflow.
 */
int gmx_feenableexcept();

/*! \brief Return cut-off to use
 *
 * Takes the max of two cut-offs. However a cut-off of 0
 * signifies that the cut-off in fact is infinite, and
 * this requires this special routine.
 * \param[in] cutoff1 The first cutoff (e.g. coulomb)
 * \param[in] cutoff2 The second cutoff (e.g. vdw)
 * \return 0 if either is 0, the normal max of the two otherwise.
 */
real max_cutoff(real cutoff1, real cutoff2);

#ifdef __cplusplus
}
#endif

#endif