/*

 * Copyright (c) 2016 Thomas Pornin <pornin@bolet.org>

 *

 * Permission is hereby granted, free of charge, to any person obtaining 

 * a copy of this software and associated documentation files (the

 * "Software"), to deal in the Software without restriction, including

 * without limitation the rights to use, copy, modify, merge, publish,

 * distribute, sublicense, and/or sell copies of the Software, and to

 * permit persons to whom the Software is furnished to do so, subject to

 * the following conditions:

 *

 * The above copyright notice and this permission notice shall be 

 * included in all copies or substantial portions of the Software.

 *

 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, 

 * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF

 * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND 

 * NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS

 * BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN

 * ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN

 * CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE

 * SOFTWARE.

 */

#include "inner.h"

/* see inner.h */

void

br_i31_from_monty(uint32_t *x, const uint32_t *m, uint32_t m0i)

{

  size_t len, u, v;

  len = (m[0] + 31) >> 5;

  for (u = 0; u < len; u ++) {

    uint32_t f;

    uint64_t cc;

    f = MUL31_lo(x[1], m0i);

    cc = 0;

    for (v = 0; v < len; v ++) {

      uint64_t z;

      z = (uint64_t)x[v + 1] + MUL31(f, m[v + 1]) + cc;

      cc = z >> 31;

      if (v != 0) {

        x[v] = (uint32_t)z & 0x7FFFFFFF;

      }

    }

    x[len] = (uint32_t)cc;

  }

  /*

   * We may have to do an extra subtraction, but only if the

   * value in x[] is indeed greater than or equal to that of m[],

   * which is why we must do two calls (first call computes the

   * carry, second call performs the subtraction only if the carry

   * is 0).

   */

  br_i31_sub(x, m, NOT(br_i31_sub(x, m, 0)));

}