src/gromacs/math/utilities.h

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  38 #ifndef GMX_MATH_UTILITIES_H
  39 #define GMX_MATH_UTILITIES_H
  40
  41 #include <limits.h>
  42
  43 #include <cmath>
  44
  45 #include "gromacs/utility/basedefinitions.h"
  46 #include "gromacs/utility/real.h"
  47
  48 #ifndef M_PI
  49 #    define M_PI 3.14159265358979323846
  50 #endif
  51
  52 #ifndef M_PI_2
  53 #    define M_PI_2 1.57079632679489661923
  54 #endif
  55
  56 #ifndef M_2PI
  57 #    define M_2PI 6.28318530717958647692
  58 #endif
  59
  60 #ifndef M_SQRT2
  61 #    define M_SQRT2 sqrt(2.0)
  62 #endif
  63
  64 #ifndef M_1_PI
  65 #    define M_1_PI 0.31830988618379067154
  66 #endif
  67
  68 #ifndef M_FLOAT_1_SQRTPI /* used in GPU kernels */
  69 /* 1.0 / sqrt(M_PI) */
  70 #    define M_FLOAT_1_SQRTPI 0.564189583547756f
  71 #endif
  72
  73 #ifndef M_1_SQRTPI
  74 /* 1.0 / sqrt(M_PI) */
  75 #    define M_1_SQRTPI 0.564189583547756
  76 #endif
  77
  78 #ifndef M_2_SQRTPI
  79 /* 2.0 / sqrt(M_PI) */
  80 #    define M_2_SQRTPI 1.128379167095513
  81 #endif
  82
  83 /*! \brief Enum to select safe or highly unsafe (faster) math functions.
  84  *
  85  *  Normally all the Gromacs math functions should apply reasonable care with
  86  *  input arguments. While we do not necessarily adhere strictly to IEEE
  87  *  (in particular not for arguments that might result in NaN, inf, etc.), the
  88  *  functions should return reasonable values or e.g. clamp results to zero.
  89  *
  90  *  However, in a few cases where we are extremely performance-sensitive it
  91  *  makes sense to forego these checks too in cases where we know the exact
  92  *  properties if the input data, and we really need to save every cycle we can.
  93  *
  94  *  This class is typically used as a template parameter to such calls to enable
  95  *  the caller to select the level of aggressiveness. We should always use the
  96  *  safe alternative as the default value, and document carefully what might
  97  *  happen with the unsafe alternative.
  98  */
  99 enum class MathOptimization
 100 {
 101     Safe,  //!< Don't do unsafe optimizations. This should always be default.
 102     Unsafe //!< Allow optimizations that can be VERY dangerous for general code.
 103 };
 104
 105 /*! \brief Check if two numbers are within a tolerance
 106  *
 107  *  This routine checks if the relative difference between two numbers is
 108  *  approximately within the given tolerance, defined as
 109  *  fabs(f1-f2)<=tolerance*fabs(f1+f2).
 110  *
 111  *  To check if two floating-point numbers are almost identical, use this routine
 112  *  with the tolerance GMX_REAL_EPS, or GMX_DOUBLE_EPS if the check should be
 113  *  done in double regardless of Gromacs precision.
 114  *
 115  *  To check if two algorithms produce similar results you will normally need
 116  *  to relax the tolerance significantly since many operations (e.g. summation)
 117  *  accumulate floating point errors.
 118  *
 119  *  \param f1  First number to compare
 120  *  \param f2  Second number to compare
 121  *  \param tol Tolerance to use
 122  *
 123  *  \return 1 if the relative difference is within tolerance, 0 if not.
 124  */
 125 bool gmx_within_tol(double f1, double f2, double tol);
 126
 127 /*!
 128  * \brief Check if a number is smaller than some preset safe minimum
 129  * value, currently defined as GMX_REAL_MIN/GMX_REAL_EPS.
 130  *
 131  * If a number is smaller than this value we risk numerical overflow
 132  * if any number larger than 1.0/GMX_REAL_EPS is divided by it.
 133  *
 134  * \return True if 'almost' numerically zero, false otherwise.
 135  */
 136 bool gmx_numzero(double a);
 137
 138 /*! \brief Multiply two large ints
 139  *
 140  * \return False iff overflow occurred
 141  */
 142 gmx_bool check_int_multiply_for_overflow(int64_t a, int64_t b, int64_t* result);
 143
 144 /*! \brief Enable floating-point exceptions if supported on OS
 145  *
 146  * Enables division-by-zero, invalid value, and overflow.
 147  *
 148  * \returns 0 if successful in enabling exceptions, anything else in case of failure/unsupported OS.
 149  */
 150 int gmx_feenableexcept();
 151
 152 /*! \brief Disable floating-point exceptions if supported on OS
 153  *
 154  * Disables division-by-zero, invalid value, and overflow.
 155  *
 156  * \returns 0 if successful in disabling exceptions, anything else in case of failure/unsupported OS.
 157  */
 158 int gmx_fedisableexcept();
 159
 160 #endif