common/transline_calculations/units.h

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/*
 * Copyright (C) 1992-2011 jean-pierre.charras
 * Copyright The KiCad Developers, see AUTHORS.txt for contributors.
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public License
 * as published by the Free Software Foundation; either version 2
 * of the License, or (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this package.  If not, see <https://www.gnu.org/licenses/>.
 *
 */
 
#ifndef TRANSLINE_CALCULATIONS_UNITS_H
#define TRANSLINE_CALCULATIONS_UNITS_H
 
 
#include <cmath>
 
 
#ifndef HAVE_CMATH_ASINH
inline double asinh( double x )
{
    return log( x + sqrt( x * x + 1 ) );
}
#endif
 
#ifndef HAVE_CMATH_ACOSH
inline double acosh( double x )
{
    // must be x>=1, if not return Nan (Not a Number)
    if( x < 1.0 )
        return sqrt( -1.0 );
 
    // return only the positive result (as sqrt does).
    return log( x + sqrt( x * x - 1.0 ) );
}
#endif
 
#ifndef HAVE_CMATH_ATANH
inline double atanh( double x )
{
    // must be x>-1, x<1, if not return Nan (Not a Number)
    if( !( x > -1.0 && x < 1.0 ) )
        return sqrt( -1.0 );
 
    return log( ( 1.0 + x ) / ( 1.0 - x ) ) / 2.0;
}
#endif
 
namespace TRANSLINE_CALCULATIONS
{
constexpr double MU0 = 12.566370614e-7; // magnetic constant
constexpr double E0 = 8.854e-12;        // permittivity of free space
constexpr double C0 = 299792458.0;      // speed of light in vacuum
 
// wave resistance in vacuum
//
// - From 1948 to 2019, Z₀ was defined to be exactly π*119.9169832 Ω (≈376.730_313_462 Ω).
//
// - The 2019 revision to SI changed it from a defined value to a measured value.  In accordance
//   with this, the "2018" revision (based on 2018 measurements, values published 2019, rationale
//   published 2021) of the "CODATA Recommended Values of the Fundamental Physical Constants"
//   (<https://tsapps.nist.gov/publication/get_pdf.cfm?pub_id=931443>) gave the accepted measured
//   value as 376.730_313_668(57) Ω (the number in parenthesis is the margin of error).
//
// - The "2022" revision (based on 2022 measurements, values published 2024, rationale published
//   2025) of CODATA (<https://tsapps.nist.gov/publication/get_pdf.cfm?pub_id=958143>) gave the
//   accepted measured value as 376.730_313_412(59) Ω.
//
// The most recent CODATA value can always be found at
// <https://physics.nist.gov/cgi-bin/cuu/Value?z0>.
//
// - From its first use in 2011 (pre-v4), KiCad used the value 376.730_313_469_585_043_649_63, which
//   mysteriously doesn't quite match any of the above.
//
// - In 2021 (v6), KiCad updated to the 2018 CODATA value.
//
// - In 2026, KiCad updated to the 2022 CODATA value.
constexpr double ZF0 = 376.730313412;
 
// const to convert a attenuation / loss from log (Neper) to decibel
// (1 Np = 8.68589 dB)
const double LOG2DB = 20.0 / log( 10.0 );
}; // namespace TRANSLINE_CALCULATIONS
 
#endif // TRANSLINE_CALCULATIONS_UNITS_H