mirror of
http://galexander.org/git/simplesshd.git
synced 2024-11-27 17:58:13 +00:00
82 lines
2.2 KiB
C
82 lines
2.2 KiB
C
#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://math.libtomcrypt.com
|
|
*/
|
|
|
|
/* 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: 1.3 $ */
|
|
/* $Date: 2006/03/31 14:18:44 $ */
|