_ Git - BearSSL/blob - src/int/i32_fmont.c

   1 /*
   2  * Copyright (c) 2016 Thomas Pornin <pornin@bolet.org>
   3  *
   4  * Permission is hereby granted, free of charge, to any person obtaining
   5  * a copy of this software and associated documentation files (the
   6  * "Software"), to deal in the Software without restriction, including
   7  * without limitation the rights to use, copy, modify, merge, publish,
   8  * distribute, sublicense, and/or sell copies of the Software, and to
   9  * permit persons to whom the Software is furnished to do so, subject to
  10  * the following conditions:
  11  *
  12  * The above copyright notice and this permission notice shall be
  13  * included in all copies or substantial portions of the Software.
  14  *
  15  * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
  16  * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
  17  * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
  18  * NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS
  19  * BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN
  20  * ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
  21  * CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
  22  * SOFTWARE.
  23  */
  24
  25 #include "inner.h"
  26
  27 /* see inner.h */
  28 void
  29 br_i32_from_monty(uint32_t *x, const uint32_t *m, uint32_t m0i)
  30 {
  31         size_t len, u, v;
  32
  33         len = (m[0] + 31) >> 5;
  34         for (u = 0; u < len; u ++) {
  35                 uint32_t f;
  36                 uint64_t cc;
  37
  38                 f = x[1] * m0i;
  39                 cc = 0;
  40                 for (v = 0; v < len; v ++) {
  41                         uint64_t z;
  42
  43                         z = (uint64_t)x[v + 1] + MUL(f, m[v + 1]) + cc;
  44                         cc = z >> 32;
  45                         if (v != 0) {
  46                                 x[v] = (uint32_t)z;
  47                         }
  48                 }
  49                 x[len] = (uint32_t)cc;
  50         }
  51
  52         /*
  53          * We may have to do an extra subtraction, but only if the
  54          * value in x[] is indeed greater than or equal to that of m[],
  55          * which is why we must do two calls (first call computes the
  56          * carry, second call performs the subtraction only if the carry
  57          * is 0).
  58          */
  59         br_i32_sub(x, m, NOT(br_i32_sub(x, m, 0)));
  60 }