1 #include "tommath_private.h"
2 #ifdef BN_S_MP_SQR_C
3 /* LibTomMath, multiple-precision integer library -- Tom St Denis */
4 /* SPDX-License-Identifier: Unlicense */
5
6 /* low level squaring, b = a*a, HAC pp.596-597, Algorithm 14.16 */
s_mp_sqr(const mp_int * a,mp_int * b)7 mp_err s_mp_sqr(const mp_int *a, mp_int *b)
8 {
9 mp_int t;
10 int ix, iy, pa;
11 mp_err err;
12 mp_word r;
13 mp_digit u, tmpx, *tmpt;
14
15 pa = a->used;
16 if ((err = mp_init_size(&t, (2 * pa) + 1)) != MP_OKAY) {
17 return err;
18 }
19
20 /* default used is maximum possible size */
21 t.used = (2 * pa) + 1;
22
23 for (ix = 0; ix < pa; ix++) {
24 /* first calculate the digit at 2*ix */
25 /* calculate double precision result */
26 r = (mp_word)t.dp[2*ix] +
27 ((mp_word)a->dp[ix] * (mp_word)a->dp[ix]);
28
29 /* store lower part in result */
30 t.dp[ix+ix] = (mp_digit)(r & (mp_word)MP_MASK);
31
32 /* get the carry */
33 u = (mp_digit)(r >> (mp_word)MP_DIGIT_BIT);
34
35 /* left hand side of A[ix] * A[iy] */
36 tmpx = a->dp[ix];
37
38 /* alias for where to store the results */
39 tmpt = t.dp + ((2 * ix) + 1);
40
41 for (iy = ix + 1; iy < pa; iy++) {
42 /* first calculate the product */
43 r = (mp_word)tmpx * (mp_word)a->dp[iy];
44
45 /* now calculate the double precision result, note we use
46 * addition instead of *2 since it's easier to optimize
47 */
48 r = (mp_word)*tmpt + r + r + (mp_word)u;
49
50 /* store lower part */
51 *tmpt++ = (mp_digit)(r & (mp_word)MP_MASK);
52
53 /* get carry */
54 u = (mp_digit)(r >> (mp_word)MP_DIGIT_BIT);
55 }
56 /* propagate upwards */
57 while (u != 0uL) {
58 r = (mp_word)*tmpt + (mp_word)u;
59 *tmpt++ = (mp_digit)(r & (mp_word)MP_MASK);
60 u = (mp_digit)(r >> (mp_word)MP_DIGIT_BIT);
61 }
62 }
63
64 mp_clamp(&t);
65 mp_exch(&t, b);
66 mp_clear(&t);
67 return MP_OKAY;
68 }
69 #endif
70