58 lines
1.3 KiB
C
58 lines
1.3 KiB
C
|
#include <tommath.h>
|
||
|
|
#ifdef BN_MP_EXPT_D_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
|
||
|
|
*/
|
||
|
|
|
||
|
|
/* calculate c = a**b using a square-multiply algorithm */
|
||
|
|
int mp_expt_d (mp_int * a, mp_digit b, mp_int * c)
|
||
|
|
{
|
||
|
|
int res, x;
|
||
|
|
mp_int g;
|
||
|
|
|
||
|
|
if ((res = mp_init_copy (&g, a)) != MP_OKAY) {
|
||
|
|
return res;
|
||
|
|
}
|
||
|
|
|
||
|
|
/* set initial result */
|
||
|
|
mp_set (c, 1);
|
||
|
|
|
||
|
|
for (x = 0; x < (int) DIGIT_BIT; x++) {
|
||
|
|
/* square */
|
||
|
|
if ((res = mp_sqr (c, c)) != MP_OKAY) {
|
||
|
|
mp_clear (&g);
|
||
|
|
return res;
|
||
|
|
}
|
||
|
|
|
||
|
|
/* if the bit is set multiply */
|
||
|
|
if ((b & (mp_digit) (((mp_digit)1) << (DIGIT_BIT - 1))) != 0) {
|
||
|
|
if ((res = mp_mul (c, &g, c)) != MP_OKAY) {
|
||
|
|
mp_clear (&g);
|
||
|
|
return res;
|
||
|
|
}
|
||
|
|
}
|
||
|
|
|
||
|
|
/* shift to next bit */
|
||
|
|
b <<= 1;
|
||
|
|
}
|
||
|
|
|
||
|
|
mp_clear (&g);
|
||
|
|
return MP_OKAY;
|
||
|
|
}
|
||
|
|
#endif
|
||
|
|
|
||
|
|
/* $Source$ */
|
||
|
|
/* $Revision: 0.41 $ */
|
||
|
|
/* $Date: 2007-04-18 09:58:18 +0000 $ */
|