tommath/bn_mp_expt_d.c

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/* LibTomMath, multiple-precision integer library -- Tom St Denis
*
* LibTomMath is library that provides for multiple-precision
* integer arithmetic as well as number theoretic functionality.
*
* The library is 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@iahu.ca, http://libtommath.iahu.ca
*/
#include <tommath.h>
int
mp_expt_d (mp_int * a, mp_digit b, mp_int * c)
{
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int res, x;
mp_int g;
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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++) {
if ((res = mp_sqr (c, c)) != MP_OKAY) {
mp_clear (&g);
return res;
}
if ((b & (mp_digit) (1 << (DIGIT_BIT - 1))) != 0) {
if ((res = mp_mul (c, &g, c)) != MP_OKAY) {
mp_clear (&g);
return res;
}
}
b <<= 1;
}
mp_clear (&g);
return MP_OKAY;
}