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40 * Declares `real` and related constants.
43 * \ingroup module_utility
45 #ifndef GMX_UTILITY_REAL_H
46 #define GMX_UTILITY_REAL_H
48 /*! \brief Double precision accuracy */
49 #define GMX_DOUBLE_EPS 2.2204460492503131e-16
51 /*! \brief Maximum double precision value - reduced 1 unit in last digit for MSVC */
52 #define GMX_DOUBLE_MAX 1.7976931348623157e+308
54 /*! \brief Minimum double precision value */
55 #define GMX_DOUBLE_MIN 2.2250738585072014e-308
57 /*! \brief Single precision accuracy */
58 #define GMX_FLOAT_EPS 1.19209290e-07F
60 /*! \brief Maximum single precision value - reduced 1 unit in last digit for MSVC */
61 #define GMX_FLOAT_MAX 3.40282346E+38F
63 /*! \brief Minimum single precision value */
64 #define GMX_FLOAT_MIN 1.175494351E-38F
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.
75 # define GMX_DOUBLE_NEGZERO \
81 } _gmx_dzero = { 0, -2147483648 }; \
84 # define GMX_FLOAT_NEGZERO \
90 } _gmx_fzero = { -2147483648 }; \
94 /*! \brief Negative zero in double */
95 # define GMX_DOUBLE_NEGZERO (-0.0)
97 /*! \brief Negative zero in float */
98 # define GMX_FLOAT_NEGZERO (-0.0F)
102 * \brief Precision-dependent \Gromacs floating-point type.
105 * \brief Used to check whether `real` is already defined.
107 /*! \def GMX_MPI_REAL
108 * \brief MPI data type for `real`.
110 /*! \def GMX_REAL_EPS
111 * \brief Accuracy for `real`.
113 /*! \def GMX_REAL_MIN
114 * \brief Smallest non-zero value for `real`.
116 /*! \def GMX_REAL_MAX
117 * \brief Largest finite value for `real`.
119 /*! \def GMX_REAL_NEGZERO
120 * \brief Negative zero for `real`.
122 /*! \def gmx_real_fullprecision_pfmt
123 * \brief Format string for full `real` precision.
125 /*! \def GMX_FLOAT_MAX_SIMD_WIDTH
126 * \brief The maximum supported number of `float` elements in a SIMD register.
128 /*! \def GMX_DOUBLE_MAX_SIMD_WIDTH
129 * \brief The maximum supported number of `double` elements in a SIMD register.
131 /*! \def GMX_REAL_MAX_SIMD_WIDTH
132 * \brief The maximum supported number of `real` elements in a SIMD register.
135 #define GMX_FLOAT_MAX_SIMD_WIDTH 16
136 #define GMX_DOUBLE_MAX_SIMD_WIDTH 8
145 # define GMX_MPI_REAL MPI_DOUBLE
146 # define GMX_REAL_EPS GMX_DOUBLE_EPS
147 # define GMX_REAL_MIN GMX_DOUBLE_MIN
148 # define GMX_REAL_MAX GMX_DOUBLE_MAX
149 # define GMX_REAL_NEGZERO GMX_DOUBLE_NEGZERO
150 # define gmx_real_fullprecision_pfmt "%21.14e"
151 # define GMX_REAL_MAX_SIMD_WIDTH GMX_DOUBLE_MAX_SIMD_WIDTH
153 #else /* GMX_DOUBLE */
160 # define GMX_MPI_REAL MPI_FLOAT
161 # define GMX_REAL_EPS GMX_FLOAT_EPS
162 # define GMX_REAL_MIN GMX_FLOAT_MIN
163 # define GMX_REAL_MAX GMX_FLOAT_MAX
164 # define GMX_REAL_NEGZERO GMX_FLOAT_NEGZERO
165 # define gmx_real_fullprecision_pfmt "%14.7e"
166 # define GMX_REAL_MAX_SIMD_WIDTH GMX_FLOAT_MAX_SIMD_WIDTH
168 #endif /* GMX_DOUBLE */
170 /*! \brief User defined literal for real numbers.
172 * Examples: 2._real, 2.5_real, .5_real. The number is always of type real.
174 * It is best to use a real constant whenever it is used only with operands which are real.
175 * If a constant is double than the compiler is forced to do operations directly involving the
176 * constant in double even if all variables are real. A constant shouldn't be real when used with
177 * double operands, because then the constant is less accurate with GMX_DOUBLE=no.
179 * See https://en.cppreference.com/w/cpp/language/user_literal for details on this lanuage feature.
181 constexpr real operator"" _real(long double x)