libcxx/test/std/utilities/time/time.cal/euclidian.h

//===----------------------------------------------------------------------===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//


//  Assumption: minValue < maxValue
//  Assumption: minValue <= rhs <= maxValue
//  Assumption: minValue <= lhs <= maxValue
//  Assumption: minValue >= 0
template <typename T, T minValue, T maxValue>
T euclidian_addition(T rhs, T lhs)
{
    const T modulus = maxValue - minValue + 1;
    T ret = rhs + lhs;
    if (ret > maxValue)
        ret -= modulus;
    return ret;
}

//  Assumption: minValue < maxValue
//  Assumption: minValue <= rhs <= maxValue
//  Assumption: minValue <= lhs <= maxValue
//  Assumption: minValue >= 0
template <typename T, T minValue, T maxValue>
T euclidian_subtraction(T lhs, T rhs)
{
    const T modulus = maxValue - minValue + 1;
    T ret = lhs - rhs;
    if (ret < minValue)
        ret += modulus;
    if (ret > maxValue)     // this can happen if T is unsigned
        ret += modulus;
    return ret;
}