_ Git - BearSSL/blob - int/i15_mulacc.c

   1 /*
   2  * Copyright (c) 2017 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_i15_mulacc(uint16_t *d, const uint16_t *a, const uint16_t *b)
  30 {
  31         size_t alen, blen, u;
  32         unsigned dl, dh;
  33
  34         alen = (a[0] + 15) >> 4;
  35         blen = (b[0] + 15) >> 4;
  36
  37         /*
  38          * Announced bit length of d[] will be the sum of the announced
  39          * bit lengths of a[] and b[]; but the lengths are encoded.
  40          */
  41         dl = (a[0] & 15) + (d[0] & 15);
  42         dh = (a[0] >> 4) + (b[0] >> 4);
  43         d[0] = (dh << 4) + dl + (~(uint16_t)(dl - 15) >> 15);
  44
  45         for (u = 0; u < blen; u ++) {
  46                 uint32_t f;
  47                 size_t v;
  48                 uint32_t cc;
  49
  50                 f = b[1 + u];
  51                 cc = 0;
  52                 for (v = 0; v < alen; v ++) {
  53                         uint32_t z;
  54
  55                         z = (uint32_t)d[1 + u + v] + MUL15(f, a[1 + v]) + cc;
  56                         cc = z >> 15;
  57                         d[1 + u + v] = z & 0x7FFF;
  58                 }
  59                 d[1 + u + alen] = cc;
  60         }
  61 }