src/gromacs/utility/real.h

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  38 /*! \file
  39  * \brief
  40  * Declares `real` and related constants.
  41  *
  42  * \inpublicapi
  43  * \ingroup module_utility
  44  */
  45 #ifndef GMX_UTILITY_REAL_H
  46 #define GMX_UTILITY_REAL_H
  47
  48 /*! \brief Double precision accuracy */
  49 #define GMX_DOUBLE_EPS 2.2204460492503131e-16
  50
  51 /*! \brief Maximum double precision value - reduced 1 unit in last digit for MSVC */
  52 #define GMX_DOUBLE_MAX 1.7976931348623157e+308
  53
  54 /*! \brief Minimum double precision value */
  55 #define GMX_DOUBLE_MIN 2.2250738585072014e-308
  56
  57 /*! \brief Single precision accuracy */
  58 #define GMX_FLOAT_EPS 1.19209290e-07F
  59
  60 /*! \brief Maximum single precision value - reduced 1 unit in last digit for MSVC */
  61 #define GMX_FLOAT_MAX 3.40282346E+38F
  62
  63 /*! \brief Minimum single precision value */
  64 #define GMX_FLOAT_MIN 1.175494351E-38F
  65
  66 #ifdef __PGI
  67 /* The portland group x86 C/C++ compilers do not treat negative zero initializers
  68  * correctly, but "optimizes" them to positive zero, so we implement it explicitly.
  69  * These constructs are optimized to simple loads at compile time. If you want to
  70  * use them on other compilers those have to support gcc preprocessor extensions.
  71  * Note: These initializers might be sensitive to the endianness (which can
  72  * be different for byte and word order), so check that it works for your platform
  73  * and add a separate section if necessary before adding to the ifdef above.
  74  */
  75 #    define GMX_DOUBLE_NEGZERO                 \
  76         ({                                     \
  77             const union {                      \
  78                 int    di[2];                  \
  79                 double d;                      \
  80             } _gmx_dzero = { 0, -2147483648 }; \
  81             _gmx_dzero.d;                      \
  82         })
  83 #    define GMX_FLOAT_NEGZERO               \
  84         ({                                  \
  85             const union {                   \
  86                 int   fi;                   \
  87                 float f;                    \
  88             } _gmx_fzero = { -2147483648 }; \
  89             _gmx_fzero.f;                   \
  90         })
  91 #else
  92 /*! \brief Negative zero in double */
  93 #    define GMX_DOUBLE_NEGZERO (-0.0)
  94
  95 /*! \brief Negative zero in float */
  96 #    define GMX_FLOAT_NEGZERO (-0.0F)
  97 #endif
  98
  99 /*! \typedef real
 100  * \brief Precision-dependent \Gromacs floating-point type.
 101  */
 102 /*! \def HAVE_REAL
 103  * \brief Used to check whether `real` is already defined.
 104  */
 105 /*! \def GMX_MPI_REAL
 106  * \brief MPI data type for `real`.
 107  */
 108 /*! \def GMX_REAL_EPS
 109  * \brief Accuracy for `real`.
 110  */
 111 /*! \def GMX_REAL_MIN
 112  * \brief Smallest non-zero value for `real`.
 113  */
 114 /*! \def GMX_REAL_MAX
 115  * \brief Largest finite value for `real`.
 116  */
 117 /*! \def GMX_REAL_NEGZERO
 118  * \brief Negative zero for `real`.
 119  */
 120 /*! \def gmx_real_fullprecision_pfmt
 121  * \brief Format string for full `real` precision.
 122  */
 123 /*! \def GMX_FLOAT_MAX_SIMD_WIDTH
 124  * \brief The maximum supported number of `float` elements in a SIMD register.
 125  */
 126 /*! \def GMX_DOUBLE_MAX_SIMD_WIDTH
 127  * \brief The maximum supported number of `double` elements in a SIMD register.
 128  */
 129 /*! \def GMX_REAL_MAX_SIMD_WIDTH
 130  * \brief The maximum supported number of `real` elements in a SIMD register.
 131  */
 132
 133 #define GMX_FLOAT_MAX_SIMD_WIDTH 16
 134 #define GMX_DOUBLE_MAX_SIMD_WIDTH 8
 135
 136 #if GMX_DOUBLE
 137
 138 #    ifndef HAVE_REAL
 139 typedef double real;
 140 #        define HAVE_REAL
 141 #    endif
 142
 143 #    define GMX_MPI_REAL MPI_DOUBLE
 144 #    define GMX_REAL_EPS GMX_DOUBLE_EPS
 145 #    define GMX_REAL_MIN GMX_DOUBLE_MIN
 146 #    define GMX_REAL_MAX GMX_DOUBLE_MAX
 147 #    define GMX_REAL_NEGZERO GMX_DOUBLE_NEGZERO
 148 #    define gmx_real_fullprecision_pfmt "%21.14e"
 149 #    define GMX_REAL_MAX_SIMD_WIDTH GMX_DOUBLE_MAX_SIMD_WIDTH
 150
 151 #else /* GMX_DOUBLE */
 152
 153 #    ifndef HAVE_REAL
 154 typedef float real;
 155 #        define HAVE_REAL
 156 #    endif
 157
 158 #    define GMX_MPI_REAL MPI_FLOAT
 159 #    define GMX_REAL_EPS GMX_FLOAT_EPS
 160 #    define GMX_REAL_MIN GMX_FLOAT_MIN
 161 #    define GMX_REAL_MAX GMX_FLOAT_MAX
 162 #    define GMX_REAL_NEGZERO GMX_FLOAT_NEGZERO
 163 #    define gmx_real_fullprecision_pfmt "%14.7e"
 164 #    define GMX_REAL_MAX_SIMD_WIDTH GMX_FLOAT_MAX_SIMD_WIDTH
 165
 166 #endif /* GMX_DOUBLE */
 167
 168 /*! \brief User defined literal for real numbers.
 169  *
 170  * Examples: 2._real, 2.5_real, .5_real. The number is always of type real.
 171  *
 172  * It is best to use a real constant whenever it is used only with operands which are real.
 173  * If a constant is double than the compiler is forced to do operations directly involving the
 174  * constant in double even if all variables are real. A constant shouldn't be real when used with
 175  * double operands, because then the constant is less accurate with GMX_DOUBLE=no.
 176  *
 177  * See https://en.cppreference.com/w/cpp/language/user_literal for details on this lanuage feature.
 178  */
 179 constexpr real operator"" _real(long double x)
 180 {
 181     return real(x);
 182 }
 183
 184 #endif