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
|
#include <tommath.h>
#ifdef BN_S_MP_MUL_HIGH_DIGS_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
*/
/* multiplies |a| * |b| and does not compute the lower digs digits
* [meant to get the higher part of the product]
*/
int s_mp_mul_high_digs(mp_int * a, mp_int * b, mp_int * c, int digs)
{
mp_int t;
int res, pa, pb, ix, iy;
mp_digit u;
mp_word r;
mp_digit tmpx, *tmpt, *tmpy;
/* can we use the fast multiplier? */
#ifdef BN_FAST_S_MP_MUL_HIGH_DIGS_C
if (((a->used + b->used + 1) < MP_WARRAY)
&& MIN(a->used,
b->used) <
(1 << ((CHAR_BIT * sizeof(mp_word)) - (2 * DIGIT_BIT)))) {
return fast_s_mp_mul_high_digs(a, b, c, digs);
}
#endif
if ((res = mp_init_size(&t, a->used + b->used + 1)) != MP_OKAY) {
return res;
}
t.used = a->used + b->used + 1;
pa = a->used;
pb = b->used;
for (ix = 0; ix < pa; ix++) {
/* clear the carry */
u = 0;
/* left hand side of A[ix] * B[iy] */
tmpx = a->dp[ix];
/* alias to the address of where the digits will be stored */
tmpt = &(t.dp[digs]);
/* alias for where to read the right hand side from */
tmpy = b->dp + (digs - ix);
for (iy = digs - ix; iy < pb; iy++) {
/* calculate the double precision result */
r = ((mp_word) * tmpt) +
((mp_word) tmpx) * ((mp_word) * tmpy++) +
((mp_word) u);
/* get the lower part */
*tmpt++ = (mp_digit) (r & ((mp_word) MP_MASK));
/* carry the carry */
u = (mp_digit) (r >> ((mp_word) DIGIT_BIT));
}
*tmpt = u;
}
mp_clamp(&t);
mp_exch(&t, c);
mp_clear(&t);
return MP_OKAY;
}
#endif
/* $Source: /cvs/libtom/libtommath/bn_s_mp_mul_high_digs.c,v $ */
/* $Revision: 1.4 $ */
/* $Date: 2006/12/28 01:25:13 $ */
|
