serenity/Userland/Applications/Calculator/Calculator.h

/*
 * Copyright (c) 2019-2020, Sergey Bugaev <bugaevc@serenityos.org>
 *
 * SPDX-License-Identifier: BSD-2-Clause
 */

#pragma once

#include "KeypadValue.h"

// This type implements the regular calculator
// behavior, such as performing arithmetic
// operations and providing a memory cell.
// It does not deal with number input; you
// have to pass in already parsed double
// values.

class Calculator final {
public:
    Calculator();
    ~Calculator();

    enum class Operation {
        None,
        Add,
        Subtract,
        Multiply,
        Divide,

        Sqrt,
        Inverse,
        Percent,
        ToggleSign,

        MemClear,
        MemRecall,
        MemSave,
        MemAdd
    };

    KeypadValue begin_operation(Operation, KeypadValue);
    KeypadValue finish_operation(KeypadValue);

    bool has_error() const { return m_has_error; }

    void clear_operation();
    void clear_error() { m_has_error = false; }

private:
    static bool should_be_rounded(KeypadValue);
    static void round(KeypadValue&);

    static constexpr auto rounding_threshold = []() consteval
    {
        using used_type = u64;

        auto count = 1;
        used_type res = 10;
        while (!__builtin_mul_overflow(res, (used_type)10, &res)) {
            count++;
        }
        return count;
    }
    ();

    Operation m_operation_in_progress { Operation::None };
    KeypadValue m_saved_argument { (i64)0 };
    KeypadValue m_mem { (i64)0 };
    bool m_has_error { false };
};