weave/src/lib/support/verhoeff/Verhoeff.cpp

/*
 *
 *    Copyright (c) 2013-2017 Nest Labs, Inc.
 *    All rights reserved.
 *
 *    Licensed under the Apache License, Version 2.0 (the "License");
 *    you may not use this file except in compliance with the License.
 *    You may obtain a copy of the License at
 *
 *        http://www.apache.org/licenses/LICENSE-2.0
 *
 *    Unless required by applicable law or agreed to in writing, software
 *    distributed under the License is distributed on an "AS IS" BASIS,
 *    WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 *    See the License for the specific language governing permissions and
 *    limitations under the License.
 */

/**
 *    @file
 *      This file implements an object for the core Verhoeff
 *      check-digit algorithm operations.
 *
 */

#include "Verhoeff.h"

int Verhoeff::DihedralMultiply(int x, int y, int n)
{
	int n2 = n * 2;

	x = x % n2;
	y = y % n2;

	if (x < n)
	{
		if (y < n)
			return  (x +  y     ) % n;
		else
			return ((x + (y - n)) % n) + n;
	}
	else
	{
		if (y < n)
			return ((n + (x - n) -  y     ) % n) + n;
		else
			return  (n + (x - n) - (y - n)) % n;
	}
}

int Verhoeff::DihedralInvert(int val, int n)
{
	if (val > 0 && val < n)
		return n - val;
	else
		return val;
}

int Verhoeff::Permute(int val, uint8_t *permTable, int permTableLen, int iterCount)
{
	val = val % permTableLen;
	if (iterCount == 0)
		return val;
	else
		return Permute(permTable[val], permTable, permTableLen, iterCount - 1);
}