mirror of
http://galexander.org/git/simplesshd.git
synced 2024-11-30 11:18:12 +00:00
63 lines
1.4 KiB
C
63 lines
1.4 KiB
C
|
#include <tommath.h>
|
||
|
|
#ifdef BN_MP_REDUCE_2K_L_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
|
||
|
|
*/
|
||
|
|
|
||
|
|
/* reduces a modulo n where n is of the form 2**p - d
|
||
|
|
This differs from reduce_2k since "d" can be larger
|
||
|
|
than a single digit.
|
||
|
|
*/
|
||
|
|
int mp_reduce_2k_l(mp_int *a, mp_int *n, mp_int *d)
|
||
|
|
{
|
||
|
|
mp_int q;
|
||
|
|
int p, res;
|
||
|
|
|
||
|
|
if ((res = mp_init(&q)) != MP_OKAY) {
|
||
|
|
return res;
|
||
|
|
}
|
||
|
|
|
||
|
|
p = mp_count_bits(n);
|
||
|
|
top:
|
||
|
|
/* q = a/2**p, a = a mod 2**p */
|
||
|
|
if ((res = mp_div_2d(a, p, &q, a)) != MP_OKAY) {
|
||
|
|
goto ERR;
|
||
|
|
}
|
||
|
|
|
||
|
|
/* q = q * d */
|
||
|
|
if ((res = mp_mul(&q, d, &q)) != MP_OKAY) {
|
||
|
|
goto ERR;
|
||
|
|
}
|
||
|
|
|
||
|
|
/* a = a + q */
|
||
|
|
if ((res = s_mp_add(a, &q, a)) != MP_OKAY) {
|
||
|
|
goto ERR;
|
||
|
|
}
|
||
|
|
|
||
|
|
if (mp_cmp_mag(a, n) != MP_LT) {
|
||
|
|
s_mp_sub(a, n, a);
|
||
|
|
goto top;
|
||
|
|
}
|
||
|
|
|
||
|
|
ERR:
|
||
|
|
mp_clear(&q);
|
||
|
|
return res;
|
||
|
|
}
|
||
|
|
|
||
|
|
#endif
|
||
|
|
|
||
|
|
/* $Source: /cvs/libtom/libtommath/bn_mp_reduce_2k_l.c,v $ */
|
||
|
|
/* $Revision: 1.3 $ */
|
||
|
|
/* $Date: 2006/03/31 14:18:44 $ */
|