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/*! \file
 * \brief
 * Declares `real` and related constants.
 *
 * \inpublicapi
 * \ingroup module_utility
 */
#ifndef GMX_UTILITY_REAL_H
#define GMX_UTILITY_REAL_H

/*! \brief Double precision accuracy */
#define GMX_DOUBLE_EPS 2.2204460492503131e-16

/*! \brief Maximum double precision value - reduced 1 unit in last digit for MSVC */
#define GMX_DOUBLE_MAX 1.7976931348623157e+308

/*! \brief Minimum double precision value */
#define GMX_DOUBLE_MIN 2.2250738585072014e-308

/*! \brief Single precision accuracy */
#define GMX_FLOAT_EPS 1.19209290e-07F

/*! \brief Maximum single precision value - reduced 1 unit in last digit for MSVC */
#define GMX_FLOAT_MAX 3.40282346E+38F

/*! \brief Minimum single precision value */
#define GMX_FLOAT_MIN 1.175494351E-38F

#ifdef __PGI
/* The portland group x86 C/C++ compilers do not treat negative zero initializers
 * correctly, but "optimizes" them to positive zero, so we implement it explicitly.
 * These constructs are optimized to simple loads at compile time. If you want to
 * use them on other compilers those have to support gcc preprocessor extensions.
 * Note: These initializers might be sensitive to the endianness (which can
 * be different for byte and word order), so check that it works for your platform
 * and add a separate section if necessary before adding to the ifdef above.
 */
#    define GMX_DOUBLE_NEGZERO                 \
        ({                                     \
            const union                        \
            {                                  \
                int    di[2];                  \
                double d;                      \
            } _gmx_dzero = { 0, -2147483648 }; \
            _gmx_dzero.d;                      \
        })
#    define GMX_FLOAT_NEGZERO               \
        ({                                  \
            const union                     \
            {                               \
                int   fi;                   \
                float f;                    \
            } _gmx_fzero = { -2147483648 }; \
            _gmx_fzero.f;                   \
        })
#else
/*! \brief Negative zero in double */
#    define GMX_DOUBLE_NEGZERO (-0.0)

/*! \brief Negative zero in float */
#    define GMX_FLOAT_NEGZERO (-0.0F)
#endif

/*! \typedef real
 * \brief Precision-dependent \Gromacs floating-point type.
 */
/*! \def HAVE_REAL
 * \brief Used to check whether `real` is already defined.
 */
/*! \def GMX_MPI_REAL
 * \brief MPI data type for `real`.
 */
/*! \def GMX_REAL_EPS
 * \brief Accuracy for `real`.
 */
/*! \def GMX_REAL_MIN
 * \brief Smallest non-zero value for `real`.
 */
/*! \def GMX_REAL_MAX
 * \brief Largest finite value for `real`.
 */
/*! \def GMX_REAL_NEGZERO
 * \brief Negative zero for `real`.
 */
/*! \def gmx_real_fullprecision_pfmt
 * \brief Format string for full `real` precision.
 */
/*! \def GMX_FLOAT_MAX_SIMD_WIDTH
 * \brief The maximum supported number of `float` elements in a SIMD register.
 */
/*! \def GMX_DOUBLE_MAX_SIMD_WIDTH
 * \brief The maximum supported number of `double` elements in a SIMD register.
 */
/*! \def GMX_REAL_MAX_SIMD_WIDTH
 * \brief The maximum supported number of `real` elements in a SIMD register.
 */

#define GMX_FLOAT_MAX_SIMD_WIDTH 16
#define GMX_DOUBLE_MAX_SIMD_WIDTH 8

#if GMX_DOUBLE

#    ifndef HAVE_REAL
typedef double real;
#        define HAVE_REAL
#    endif

#    define GMX_MPI_REAL MPI_DOUBLE
#    define GMX_REAL_EPS GMX_DOUBLE_EPS
#    define GMX_REAL_MIN GMX_DOUBLE_MIN
#    define GMX_REAL_MAX GMX_DOUBLE_MAX
#    define GMX_REAL_NEGZERO GMX_DOUBLE_NEGZERO
#    define gmx_real_fullprecision_pfmt "%21.14e"
#    define GMX_REAL_MAX_SIMD_WIDTH GMX_DOUBLE_MAX_SIMD_WIDTH

#else /* GMX_DOUBLE */

#    ifndef HAVE_REAL
typedef float real;
#        define HAVE_REAL
#    endif

#    define GMX_MPI_REAL MPI_FLOAT
#    define GMX_REAL_EPS GMX_FLOAT_EPS
#    define GMX_REAL_MIN GMX_FLOAT_MIN
#    define GMX_REAL_MAX GMX_FLOAT_MAX
#    define GMX_REAL_NEGZERO GMX_FLOAT_NEGZERO
#    define gmx_real_fullprecision_pfmt "%14.7e"
#    define GMX_REAL_MAX_SIMD_WIDTH GMX_FLOAT_MAX_SIMD_WIDTH

#endif /* GMX_DOUBLE */

/*! \brief User defined literal for real numbers.
 *
 * Examples: 2._real, 2.5_real, .5_real. The number is always of type real.
 *
 * It is best to use a real constant whenever it is used only with operands which are real.
 * If a constant is double than the compiler is forced to do operations directly involving the
 * constant in double even if all variables are real. A constant shouldn't be real when used with
 * double operands, because then the constant is less accurate with GMX_DOUBLE=no.
 *
 * See https://en.cppreference.com/w/cpp/language/user_literal for details on this lanuage feature.
 */
constexpr real operator"" _real(long double x)
{
    return real(x);
}

#endif
