80 lines
1.9 KiB
C
80 lines
1.9 KiB
C
#include "tommath_private.h"
|
|
#ifdef BN_MP_EXPT_D_EX_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.
|
|
*
|
|
* SPDX-License-Identifier: Unlicense
|
|
*/
|
|
|
|
/* calculate c = a**b using a square-multiply algorithm */
|
|
int mp_expt_d_ex(const mp_int *a, mp_digit b, mp_int *c, int fast)
|
|
{
|
|
int res;
|
|
unsigned int x;
|
|
|
|
mp_int g;
|
|
|
|
if ((res = mp_init_copy(&g, a)) != MP_OKAY) {
|
|
return res;
|
|
}
|
|
|
|
/* set initial result */
|
|
mp_set(c, 1uL);
|
|
|
|
if (fast != 0) {
|
|
while (b > 0u) {
|
|
/* if the bit is set multiply */
|
|
if ((b & 1u) != 0u) {
|
|
if ((res = mp_mul(c, &g, c)) != MP_OKAY) {
|
|
mp_clear(&g);
|
|
return res;
|
|
}
|
|
}
|
|
|
|
/* square */
|
|
if (b > 1u) {
|
|
if ((res = mp_sqr(&g, &g)) != MP_OKAY) {
|
|
mp_clear(&g);
|
|
return res;
|
|
}
|
|
}
|
|
|
|
/* shift to next bit */
|
|
b >>= 1;
|
|
}
|
|
} else {
|
|
for (x = 0; x < (unsigned)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)1 << (DIGIT_BIT - 1))) != 0u) {
|
|
if ((res = mp_mul(c, &g, c)) != MP_OKAY) {
|
|
mp_clear(&g);
|
|
return res;
|
|
}
|
|
}
|
|
|
|
/* shift to next bit */
|
|
b <<= 1;
|
|
}
|
|
} /* if ... else */
|
|
|
|
mp_clear(&g);
|
|
return MP_OKAY;
|
|
}
|
|
#endif
|
|
|
|
/* ref: $Format:%D$ */
|
|
/* git commit: $Format:%H$ */
|
|
/* commit time: $Format:%ai$ */
|