src/third_party/icu/source/i18n/units_converter.h

// © 2020 and later: Unicode, Inc. and others.
// License & terms of use: http://www.unicode.org/copyright.html

#include "unicode/utypes.h"

#if !UCONFIG_NO_FORMATTING
#ifndef __UNITS_CONVERTER_H__
#define __UNITS_CONVERTER_H__

#include "cmemory.h"
#include "measunit_impl.h"
#include "unicode/errorcode.h"
#include "unicode/stringpiece.h"
#include "unicode/uobject.h"
#include "units_converter.h"
#include "units_data.h"

U_NAMESPACE_BEGIN
namespace units {

/* Internal Structure */

enum Constants {
    CONSTANT_FT2M,    // ft2m stands for foot to meter.
    CONSTANT_PI,      // PI
    CONSTANT_GRAVITY, // Gravity
    CONSTANT_G,
    CONSTANT_GAL_IMP2M3, // Gallon imp to m3
    CONSTANT_LB2KG,      // Pound to Kilogram

    // Must be the last element.
    CONSTANTS_COUNT
};

// These values are a hard-coded subset of unitConstants in the units
// resources file. A unit test checks that all constants in the resource
// file are at least recognised by the code. Derived constants' values or
// hard-coded derivations are not checked.
static const double constantsValues[CONSTANTS_COUNT] = {
    0.3048,                    // CONSTANT_FT2M
    411557987.0 / 131002976.0, // CONSTANT_PI
    9.80665,                   // CONSTANT_GRAVITY
    6.67408E-11,               // CONSTANT_G
    0.00454609,                // CONSTANT_GAL_IMP2M3
    0.45359237,                // CONSTANT_LB2KG
};

typedef enum Signum {
    NEGATIVE = -1,
    POSITIVE = 1,
} Signum;

/* Represents a conversion factor */
struct U_I18N_API Factor {
    double factorNum = 1;
    double factorDen = 1;
    double offset = 0;
    bool reciprocal = false;
    int32_t constants[CONSTANTS_COUNT] = {};

    void multiplyBy(const Factor &rhs);
    void divideBy(const Factor &rhs);

    // Apply the power to the factor.
    void power(int32_t power);

    // Flip the `Factor`, for example, factor= 2/3, flippedFactor = 3/2
    void flip();

    // Apply SI prefix to the `Factor`
    void applySiPrefix(UMeasureSIPrefix siPrefix);
    void substituteConstants();
};

/*
 * Adds a single factor element to the `Factor`. e.g "ft3m", "2.333" or "cup2m3". But not "cup2m3^3".
 */
void U_I18N_API addSingleFactorConstant(StringPiece baseStr, int32_t power, Signum sigNum,
                                        Factor &factor, UErrorCode &status);

/**
 * Represents the conversion rate between `source` and `target`.
 */
struct U_I18N_API ConversionRate : public UMemory {
    const MeasureUnitImpl source;
    const MeasureUnitImpl target;
    double factorNum = 1;
    double factorDen = 1;
    double sourceOffset = 0;
    double targetOffset = 0;
    bool reciprocal = false;

    ConversionRate(MeasureUnitImpl &&source, MeasureUnitImpl &&target)
        : source(std::move(source)), target(std::move(target)) {}
};

enum Convertibility {
    RECIPROCAL,
    CONVERTIBLE,
    UNCONVERTIBLE,
};

MeasureUnitImpl U_I18N_API extractCompoundBaseUnit(const MeasureUnitImpl &source,
                                                   const ConversionRates &conversionRates,
                                                   UErrorCode &status);

/**
 * Check if the convertibility between `source` and `target`.
 * For example:
 *    `meter` and `foot` are `CONVERTIBLE`.
 *    `meter-per-second` and `second-per-meter` are `RECIPROCAL`.
 *    `meter` and `pound` are `UNCONVERTIBLE`.
 *
 * NOTE:
 *    Only works with SINGLE and COMPOUND units. If one of the units is a
 *    MIXED unit, an error will occur. For more information, see UMeasureUnitComplexity.
 */
Convertibility U_I18N_API extractConvertibility(const MeasureUnitImpl &source,
                                                const MeasureUnitImpl &target,
                                                const ConversionRates &conversionRates,
                                                UErrorCode &status);

/**
 * Converts from a source `MeasureUnit` to a target `MeasureUnit`.
 *
 * NOTE:
 *    Only works with SINGLE and COMPOUND units. If one of the units is a
 *    MIXED unit, an error will occur. For more information, see UMeasureUnitComplexity.
 */
class U_I18N_API UnitConverter : public UMemory {
  public:
    /**
     * Constructor of `UnitConverter`.
     * NOTE:
     *   - source and target must be under the same category
     *      - e.g. meter to mile --> both of them are length units.
     *
     * @param source represents the source unit.
     * @param target represents the target unit.
     * @param ratesInfo Contains all the needed conversion rates.
     * @param status
     */
    UnitConverter(const MeasureUnitImpl &source, const MeasureUnitImpl &target,
                  const ConversionRates &ratesInfo, UErrorCode &status);

    /**
     * Convert a measurement expressed in the source unit to a measurement
     * expressed in the target unit.
     *
     * @param inputValue the value to be converted.
     * @return the converted value.
     */
    double convert(double inputValue) const;

    /**
     * The inverse of convert(): convert a measurement expressed in the target
     * unit to a measurement expressed in the source unit.
     *
     * @param inputValue the value to be converted.
     * @return the converted value.
     */
    double convertInverse(double inputValue) const;

  private:
    ConversionRate conversionRate_;
};

} // namespace units
U_NAMESPACE_END

#endif //__UNITS_CONVERTER_H__

#endif /* #if !UCONFIG_NO_FORMATTING */