zircon/system/ulib/hid-parser/include/hid-parser/units.h

// Copyright 2019 The Fuchsia Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#ifndef HID_PARSER_UNITS_H_
#define HID_PARSER_UNITS_H_

#include <hid-parser/parser.h>
#include <stdint.h>

namespace hid {
namespace unit {

// Each system defines the units for the following measurements:
// length, mass, time, temperature, current, luminous intensity.
enum class System : int8_t {
    // SI Linear has the following units:
    // centimeter, gram, seconds, kelvin, ampere, candela.
    si_linear = 0x1,
    // SI Rotation has the following units:
    // radians, gram, seconds, kelvin, ampere, candela.
    si_rotation = 0x2,
    // English Linear has the following units:
    // inch, slug, seconds, fahrenheit, ampere, candela.
    eng_linear = 0x3,
    // English Rotation has the following units:
    // degrees, slug, seconds, fahrenheit, ampere, candela.
    eng_rotation = 0x4,
    reserved = 0x5,
};

// Sets a Unit's system. A unit can only belong to a single system.
// Calling SetSystem on a Unit that already has a system defined
// will overwrite the current system.
void SetSystem(Unit& unit, hid::unit::System system);
hid::unit::System GetSystem(const Unit& unit);

// The functions below set the exponent for various measurements.
// exp must be within [-8, 7].
// The measurement's unit is defined by the Unit's system.
// Example: Momentum is (mass * distance / time) so it has a mass
//          exponent of 1, a distance exponent of 1, and a time
//          exponent of -1. Under the SI Linear system this would
//          be (gram * centimeter / seconds).
void SetLengthExp(Unit& unit, int8_t exp);
void SetMassExp(Unit& unit, int8_t exp);
void SetTimeExp(Unit& unit, int8_t exp);
void SetTemperatureExp(Unit& unit, int8_t exp);
void SetCurrentExp(Unit& unit, int8_t exp);
void SetLuminousExp(Unit& unit, int8_t exp);

// The functions below get the exponent for various measurements.
// The return value will be within [-8, 7].
int GetLengthExp(const Unit& unit);
int GetMassExp(const Unit& unit);
int GetTimeExp(const Unit& unit);
int GetTemperatureExp(const Unit& unit);
int GetCurrentExp(const Unit& unit);
int GetLuminousExp(const Unit& unit);

// Convert a value from one unit to another.
// Returns False if it is impossible to do the conversion.
bool ConvertUnits(const Unit& unit_in, double val_in, const Unit& unit_out, double* val_out);

} // namespace unit
} // namespace hid

#endif // HID_PARSER_UNITS_H_