1*0957b409SSimon J. Gerraty /*
2*0957b409SSimon J. Gerraty * Copyright (c) 2016 Thomas Pornin <pornin@bolet.org>
3*0957b409SSimon J. Gerraty *
4*0957b409SSimon J. Gerraty * Permission is hereby granted, free of charge, to any person obtaining
5*0957b409SSimon J. Gerraty * a copy of this software and associated documentation files (the
6*0957b409SSimon J. Gerraty * "Software"), to deal in the Software without restriction, including
7*0957b409SSimon J. Gerraty * without limitation the rights to use, copy, modify, merge, publish,
8*0957b409SSimon J. Gerraty * distribute, sublicense, and/or sell copies of the Software, and to
9*0957b409SSimon J. Gerraty * permit persons to whom the Software is furnished to do so, subject to
10*0957b409SSimon J. Gerraty * the following conditions:
11*0957b409SSimon J. Gerraty *
12*0957b409SSimon J. Gerraty * The above copyright notice and this permission notice shall be
13*0957b409SSimon J. Gerraty * included in all copies or substantial portions of the Software.
14*0957b409SSimon J. Gerraty *
15*0957b409SSimon J. Gerraty * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
16*0957b409SSimon J. Gerraty * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
17*0957b409SSimon J. Gerraty * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
18*0957b409SSimon J. Gerraty * NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS
19*0957b409SSimon J. Gerraty * BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN
20*0957b409SSimon J. Gerraty * ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
21*0957b409SSimon J. Gerraty * CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
22*0957b409SSimon J. Gerraty * SOFTWARE.
23*0957b409SSimon J. Gerraty */
24*0957b409SSimon J. Gerraty
25*0957b409SSimon J. Gerraty #include "inner.h"
26*0957b409SSimon J. Gerraty
27*0957b409SSimon J. Gerraty /* see inner.h */
28*0957b409SSimon J. Gerraty void
br_i31_from_monty(uint32_t * x,const uint32_t * m,uint32_t m0i)29*0957b409SSimon J. Gerraty br_i31_from_monty(uint32_t *x, const uint32_t *m, uint32_t m0i)
30*0957b409SSimon J. Gerraty {
31*0957b409SSimon J. Gerraty size_t len, u, v;
32*0957b409SSimon J. Gerraty
33*0957b409SSimon J. Gerraty len = (m[0] + 31) >> 5;
34*0957b409SSimon J. Gerraty for (u = 0; u < len; u ++) {
35*0957b409SSimon J. Gerraty uint32_t f;
36*0957b409SSimon J. Gerraty uint64_t cc;
37*0957b409SSimon J. Gerraty
38*0957b409SSimon J. Gerraty f = MUL31_lo(x[1], m0i);
39*0957b409SSimon J. Gerraty cc = 0;
40*0957b409SSimon J. Gerraty for (v = 0; v < len; v ++) {
41*0957b409SSimon J. Gerraty uint64_t z;
42*0957b409SSimon J. Gerraty
43*0957b409SSimon J. Gerraty z = (uint64_t)x[v + 1] + MUL31(f, m[v + 1]) + cc;
44*0957b409SSimon J. Gerraty cc = z >> 31;
45*0957b409SSimon J. Gerraty if (v != 0) {
46*0957b409SSimon J. Gerraty x[v] = (uint32_t)z & 0x7FFFFFFF;
47*0957b409SSimon J. Gerraty }
48*0957b409SSimon J. Gerraty }
49*0957b409SSimon J. Gerraty x[len] = (uint32_t)cc;
50*0957b409SSimon J. Gerraty }
51*0957b409SSimon J. Gerraty
52*0957b409SSimon J. Gerraty /*
53*0957b409SSimon J. Gerraty * We may have to do an extra subtraction, but only if the
54*0957b409SSimon J. Gerraty * value in x[] is indeed greater than or equal to that of m[],
55*0957b409SSimon J. Gerraty * which is why we must do two calls (first call computes the
56*0957b409SSimon J. Gerraty * carry, second call performs the subtraction only if the carry
57*0957b409SSimon J. Gerraty * is 0).
58*0957b409SSimon J. Gerraty */
59*0957b409SSimon J. Gerraty br_i31_sub(x, m, NOT(br_i31_sub(x, m, 0)));
60*0957b409SSimon J. Gerraty }
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