47 lines
878 B
C
47 lines
878 B
C
#include "tommath_private.h"
|
|
#ifdef BN_MP_EXPT_U32_C
|
|
/* LibTomMath, multiple-precision integer library -- Tom St Denis */
|
|
/* SPDX-License-Identifier: Unlicense */
|
|
|
|
/* calculate c = a**b using a square-multiply algorithm */
|
|
mp_err mp_expt_u32(const mp_int *a, uint32_t b, mp_int *c)
|
|
{
|
|
mp_err err;
|
|
|
|
mp_int g;
|
|
|
|
if ((err = mp_init_copy(&g, a)) != MP_OKAY) {
|
|
return err;
|
|
}
|
|
|
|
/* set initial result */
|
|
mp_set(c, 1uL);
|
|
|
|
while (b > 0u) {
|
|
/* if the bit is set multiply */
|
|
if ((b & 1u) != 0u) {
|
|
if ((err = mp_mul(c, &g, c)) != MP_OKAY) {
|
|
goto LBL_ERR;
|
|
}
|
|
}
|
|
|
|
/* square */
|
|
if (b > 1u) {
|
|
if ((err = mp_sqr(&g, &g)) != MP_OKAY) {
|
|
goto LBL_ERR;
|
|
}
|
|
}
|
|
|
|
/* shift to next bit */
|
|
b >>= 1;
|
|
}
|
|
|
|
err = MP_OKAY;
|
|
|
|
LBL_ERR:
|
|
mp_clear(&g);
|
|
return err;
|
|
}
|
|
|
|
#endif
|