src/gromacs/math/utilities.h

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  37 #ifndef GMX_MATH_UTILITIES_H
  38 #define GMX_MATH_UTILITIES_H
  39
  40 #include <limits.h>
  41
  42 #include <cmath>
  43
  44 #include "gromacs/utility/basedefinitions.h"
  45 #include "gromacs/utility/real.h"
  46
  47 #ifdef __cplusplus
  48 extern "C" {
  49 #endif
  50
  51 #ifndef M_PI
  52 #define M_PI        3.14159265358979323846
  53 #endif
  54
  55 #ifndef M_PI_2
  56 #define M_PI_2      1.57079632679489661923
  57 #endif
  58
  59 #ifndef M_2PI
  60 #define M_2PI       6.28318530717958647692
  61 #endif
  62
  63 #ifndef M_SQRT2
  64 #define M_SQRT2 sqrt(2.0)
  65 #endif
  66
  67 #ifndef M_1_PI
  68 #define M_1_PI      0.31830988618379067154
  69 #endif
  70
  71 #ifndef M_FLOAT_1_SQRTPI /* used in GPU kernels */
  72 /* 1.0 / sqrt(M_PI) */
  73 #define M_FLOAT_1_SQRTPI 0.564189583547756f
  74 #endif
  75
  76 #ifndef M_1_SQRTPI
  77 /* 1.0 / sqrt(M_PI) */
  78 #define M_1_SQRTPI 0.564189583547756
  79 #endif
  80
  81 #ifndef M_2_SQRTPI
  82 /* 2.0 / sqrt(M_PI) */
  83 #define M_2_SQRTPI  1.128379167095513
  84 #endif
  85
  86 /*! \brief Enum to select safe or highly unsafe (faster) math functions.
  87  *
  88  *  Normally all the Gromacs math functions should apply reasonable care with
  89  *  input arguments. While we do not necessarily adhere strictly to IEEE
  90  *  (in particular not for arguments that might result in NaN, inf, etc.), the
  91  *  functions should return reasonable values or e.g. clamp results to zero.
  92  *
  93  *  However, in a few cases where we are extremely performance-sensitive it
  94  *  makes sense to forego these checks too in cases where we know the exact
  95  *  properties if the input data, and we really need to save every cycle we can.
  96  *
  97  *  This class is typically used as a template parameter to such calls to enable
  98  *  the caller to select the level of aggressiveness. We should always use the
  99  *  safe alternative as the default value, and document carefully what might
 100  *  happen with the unsafe alternative.
 101  */
 102 enum class MathOptimization
 103 {
 104     Safe,    //!< Don't do unsafe optimizations. This should always be default.
 105     Unsafe   //!< Allow optimizations that can be VERY dangerous for general code.
 106 };
 107
 108 /*! \brief Check if two numbers are within a tolerance
 109  *
 110  *  This routine checks if the relative difference between two numbers is
 111  *  approximately within the given tolerance, defined as
 112  *  fabs(f1-f2)<=tolerance*fabs(f1+f2).
 113  *
 114  *  To check if two floating-point numbers are almost identical, use this routine
 115  *  with the tolerance GMX_REAL_EPS, or GMX_DOUBLE_EPS if the check should be
 116  *  done in double regardless of Gromacs precision.
 117  *
 118  *  To check if two algorithms produce similar results you will normally need
 119  *  to relax the tolerance significantly since many operations (e.g. summation)
 120  *  accumulate floating point errors.
 121  *
 122  *  \param f1  First number to compare
 123  *  \param f2  Second number to compare
 124  *  \param tol Tolerance to use
 125  *
 126  *  \return 1 if the relative difference is within tolerance, 0 if not.
 127  */
 128 int
 129 gmx_within_tol(double   f1,
 130                double   f2,
 131                double   tol);
 132
 133 /*!
 134  * \brief Check if a number is smaller than some preset safe minimum
 135  * value, currently defined as GMX_REAL_MIN/GMX_REAL_EPS.
 136  *
 137  * If a number is smaller than this value we risk numerical overflow
 138  * if any number larger than 1.0/GMX_REAL_EPS is divided by it.
 139  *
 140  * \return 1  if 'almost' numerically zero, 0 otherwise.
 141  */
 142 int
 143 gmx_numzero(double a);
 144
 145 /*! \brief Multiply two large ints
 146  *
 147  * \return False iff overflow occurred
 148  */
 149 gmx_bool
 150 check_int_multiply_for_overflow(gmx_int64_t  a,
 151                                 gmx_int64_t  b,
 152                                 gmx_int64_t *result);
 153
 154 /*! \brief Find greatest common divisor of two numbers
 155  *
 156  * \return GCD of the two inputs
 157  */
 158 int
 159 gmx_greatest_common_divisor(int p, int q);
 160
 161
 162 /*! \brief Enable floating-point exceptions if supported on OS
 163  *
 164  * Enables division-by-zero, invalid, and overflow.
 165  */
 166 int gmx_feenableexcept();
 167
 168 /*! \brief Return cut-off to use
 169  *
 170  * Takes the max of two cut-offs. However a cut-off of 0
 171  * signifies that the cut-off in fact is infinite, and
 172  * this requires this special routine.
 173  * \param[in] cutoff1 The first cutoff (e.g. coulomb)
 174  * \param[in] cutoff2 The second cutoff (e.g. vdw)
 175  * \return 0 if either is 0, the normal max of the two otherwise.
 176  */
 177 real max_cutoff(real cutoff1, real cutoff2);
 178
 179 #ifdef __cplusplus
 180 }
 181 #endif
 182
 183 #endif