/*
 * Copyright (C) 2022 - 2026, Stephan Mueller <smueller@chronox.de>
 *
 * License: see LICENSE file in root directory
 *
 * THIS SOFTWARE IS PROVIDED ``AS IS'' AND ANY EXPRESS OR IMPLIED
 * WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE, ALL OF
 * WHICH ARE HEREBY DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR BE
 * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
 * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT
 * OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR
 * BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
 * LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE
 * USE OF THIS SOFTWARE, EVEN IF NOT ADVISED OF THE POSSIBILITY OF SUCH
 * DAMAGE.
 */
/*
 * This code is derived in parts from the code distribution provided with
 * https://github.com/pq-crystals/dilithium
 *
 * That code is released under Public Domain
 * (https://creativecommons.org/share-your-work/public-domain/cc0/);
 * or Apache 2.0 License (https://www.apache.org/licenses/LICENSE-2.0.html).
 */

#include "dilithium_rounding.h"
#include "sidechannel_resistance.h"

/**
 * @brief power2round - For finite field element a, compute a0, a1 such that
 *			a mod^+ Q = a1*2^D + a0 with -2^{D-1} < a0 <= 2^{D-1}.
 *			Assumes a to be standard representative.
 *
 * @param [in] a input element
 * @param [out] a0 pointer to output element a0
 *
 * @return a1.
 */
int32_t power2round(int32_t *a0, int32_t a)
{
	int32_t a1;

	a1 = (a + (1 << (LC_DILITHIUM_D - 1)) - 1) >> LC_DILITHIUM_D;
	*a0 = a - (a1 << LC_DILITHIUM_D);
	return a1;
}
