### view libtommath/bn_mp_expt_d_ex.c @ 1549:5212630893ab

only clean libtom when using bundled libraries
author Matt Johnston Mon, 26 Feb 2018 23:13:54 +0800 8bba51a55704 f52919ffd3b1
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```#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
*
* The library is free for all purposes without any express
* guarantee it works.
*
* Tom St Denis, [email protected], http://libtom.org
*/

/* calculate c = a**b  using a square-multiply algorithm */
int mp_expt_d_ex (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, 1);

if (fast != 0) {
while (b > 0) {
/* if the bit is set multiply */
if ((b & 1) != 0) {
if ((res = mp_mul (c, &g, c)) != MP_OKAY) {
mp_clear (&g);
return res;
}
}

/* square */
if (b > 1) {
if ((res = mp_sqr (&g, &g)) != MP_OKAY) {
mp_clear (&g);
return res;
}
}

/* shift to next bit */
b >>= 1;
}
}
else {
for (x = 0; x < 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;
}
} /* if ... else */

mp_clear (&g);
return MP_OKAY;
}
#endif

/* ref:         \$Format:%D\$ */
/* git commit:  \$Format:%H\$ */
/* commit time: \$Format:%ai\$ */
```