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39 * Declares `real` and related constants.
42 * \ingroup module_utility
44 #ifndef GMX_UTILITY_REAL_H
45 #define GMX_UTILITY_REAL_H
47 /*! \brief Double precision accuracy */
48 #define GMX_DOUBLE_EPS 2.2204460492503131e-16
50 /*! \brief Maximum double precision value - reduced 1 unit in last digit for MSVC */
51 #define GMX_DOUBLE_MAX 1.7976931348623157e+308
53 /*! \brief Minimum double precision value */
54 #define GMX_DOUBLE_MIN 2.2250738585072014e-308
56 /*! \brief Single precision accuracy */
57 #define GMX_FLOAT_EPS 1.19209290e-07F
59 /*! \brief Maximum single precision value - reduced 1 unit in last digit for MSVC */
60 #define GMX_FLOAT_MAX 3.40282346E+38F
62 /*! \brief Minimum single precision value */
63 #define GMX_FLOAT_MIN 1.175494351E-38F
66 /* The portland group x86 C/C++ compilers do not treat negative zero initializers
67 * correctly, but "optimizes" them to positive zero, so we implement it explicitly.
68 * These constructs are optimized to simple loads at compile time. If you want to
69 * use them on other compilers those have to support gcc preprocessor extensions.
70 * Note: These initializers might be sensitive to the endianness (which can
71 * be different for byte and word order), so check that it works for your platform
72 * and add a separate section if necessary before adding to the ifdef above.
74 # define GMX_DOUBLE_NEGZERO ({ const union { int di[2]; double d; } _gmx_dzero = {0, -2147483648}; _gmx_dzero.d; })
75 # define GMX_FLOAT_NEGZERO ({ const union { int fi; float f; } _gmx_fzero = {-2147483648}; _gmx_fzero.f; })
77 /*! \brief Negative zero in double */
78 # define GMX_DOUBLE_NEGZERO (-0.0)
80 /*! \brief Negative zero in float */
81 # define GMX_FLOAT_NEGZERO (-0.0f)
85 * \brief Precision-dependent \Gromacs floating-point type.
88 * \brief Used to check whether `real` is already defined.
91 * \brief MPI data type for `real`.
94 * \brief Accuracy for `real`.
97 * \brief Smallest non-zero value for `real`.
100 * \brief Largest finite value for `real`.
102 /*! \def GMX_REAL_NEGZERO
103 * \brief Negative zero for `real`.
105 /*! \def gmx_real_fullprecision_pfmt
106 * \brief Format string for full `real` precision.
108 /*! \def GMX_REAL_MAX_SIMD_WIDTH
109 * \brief The maximum supported number of `real` elements in a SIMD register.
118 #define GMX_MPI_REAL MPI_DOUBLE
119 #define GMX_REAL_EPS GMX_DOUBLE_EPS
120 #define GMX_REAL_MIN GMX_DOUBLE_MIN
121 #define GMX_REAL_MAX GMX_DOUBLE_MAX
122 #define GMX_REAL_NEGZERO GMX_DOUBLE_NEGZERO
123 #define gmx_real_fullprecision_pfmt "%21.14e"
124 #define GMX_REAL_MAX_SIMD_WIDTH 8
126 #else /* GMX_DOUBLE */
133 #define GMX_MPI_REAL MPI_FLOAT
134 #define GMX_REAL_EPS GMX_FLOAT_EPS
135 #define GMX_REAL_MIN GMX_FLOAT_MIN
136 #define GMX_REAL_MAX GMX_FLOAT_MAX
137 #define GMX_REAL_NEGZERO GMX_FLOAT_NEGZERO
138 #define gmx_real_fullprecision_pfmt "%14.7e"
139 #define GMX_REAL_MAX_SIMD_WIDTH 16
141 #endif /* GMX_DOUBLE */
144 /*! \brief User defined literal for real numbers.
146 * Examples: 2._real, 2.5_real, .5_real. The number is always of type real.
148 * It is best to use a real constant whenever it is used only with operands which are real.
149 * If a constant is double than the compiler is forced to do operations directly involving the constant
150 * in double even if all variables are real. A constant shouldn't be real when used with double operands,
151 * because then the constant is less accurate with GMX_DOUBLE=no.
153 * See https://en.cppreference.com/w/cpp/language/user_literal for details on this lanuage feature.
155 constexpr real operator"" _real(long double x) { return real(x); }