1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
|
#include <tommath.h>
#ifdef BN_S_MP_SQR_C
/* LibTomMath, multiple-precision integer library -- Tom St Denis
*
* LibTomMath is a library that provides multiple-precision
* integer arithmetic as well as number theoretic functionality.
*
* The library was designed directly after the MPI library by
* Michael Fromberger but has been written from scratch with
* additional optimizations in place.
*
* The library is free for all purposes without any express
* guarantee it works.
*
* Tom St Denis, tomstdenis@gmail.com, http://libtom.org
*/
/* low level squaring, b = a*a, HAC pp.596-597, Algorithm 14.16 */
int s_mp_sqr(mp_int * a, mp_int * b)
{
mp_int t;
int res, ix, iy, pa;
mp_word r;
mp_digit u, tmpx, *tmpt;
pa = a->used;
if ((res = mp_init_size(&t, 2 * pa + 1)) != MP_OKAY) {
return res;
}
/* default used is maximum possible size */
t.used = 2 * pa + 1;
for (ix = 0; ix < pa; ix++) {
/* first calculate the digit at 2*ix */
/* calculate double precision result */
r = ((mp_word) t.dp[2 * ix]) +
((mp_word) a->dp[ix]) * ((mp_word) a->dp[ix]);
/* store lower part in result */
t.dp[ix + ix] = (mp_digit) (r & ((mp_word) MP_MASK));
/* get the carry */
u = (mp_digit) (r >> ((mp_word) DIGIT_BIT));
/* left hand side of A[ix] * A[iy] */
tmpx = a->dp[ix];
/* alias for where to store the results */
tmpt = t.dp + (2 * ix + 1);
for (iy = ix + 1; iy < pa; iy++) {
/* first calculate the product */
r = ((mp_word) tmpx) * ((mp_word) a->dp[iy]);
/* now calculate the double precision result, note we use
* addition instead of *2 since it's easier to optimize
*/
r = ((mp_word) * tmpt) + r + r + ((mp_word) u);
/* store lower part */
*tmpt++ = (mp_digit) (r & ((mp_word) MP_MASK));
/* get carry */
u = (mp_digit) (r >> ((mp_word) DIGIT_BIT));
}
/* propagate upwards */
while (u != ((mp_digit) 0)) {
r = ((mp_word) * tmpt) + ((mp_word) u);
*tmpt++ = (mp_digit) (r & ((mp_word) MP_MASK));
u = (mp_digit) (r >> ((mp_word) DIGIT_BIT));
}
}
mp_clamp(&t);
mp_exch(&t, b);
mp_clear(&t);
return MP_OKAY;
}
#endif
/* $Source: /cvs/libtom/libtommath/bn_s_mp_sqr.c,v $ */
/* $Revision: 1.4 $ */
/* $Date: 2006/12/28 01:25:13 $ */
|
