52 lines
1.1 KiB
C
52 lines
1.1 KiB
C
#include "tommath_private.h"
|
|
#ifdef BN_MP_RSHD_C
|
|
/* LibTomMath, multiple-precision integer library -- Tom St Denis */
|
|
/* SPDX-License-Identifier: Unlicense */
|
|
|
|
/* shift right a certain amount of digits */
|
|
void mp_rshd(mp_int *a, int b)
|
|
{
|
|
int x;
|
|
mp_digit *bottom, *top;
|
|
|
|
/* if b <= 0 then ignore it */
|
|
if (b <= 0) {
|
|
return;
|
|
}
|
|
|
|
/* if b > used then simply zero it and return */
|
|
if (a->used <= b) {
|
|
mp_zero(a);
|
|
return;
|
|
}
|
|
|
|
/* shift the digits down */
|
|
|
|
/* bottom */
|
|
bottom = a->dp;
|
|
|
|
/* top [offset into digits] */
|
|
top = a->dp + b;
|
|
|
|
/* this is implemented as a sliding window where
|
|
* the window is b-digits long and digits from
|
|
* the top of the window are copied to the bottom
|
|
*
|
|
* e.g.
|
|
|
|
b-2 | b-1 | b0 | b1 | b2 | ... | bb | ---->
|
|
/\ | ---->
|
|
\-------------------/ ---->
|
|
*/
|
|
for (x = 0; x < (a->used - b); x++) {
|
|
*bottom++ = *top++;
|
|
}
|
|
|
|
/* zero the top digits */
|
|
MP_ZERO_DIGITS(bottom, a->used - x);
|
|
|
|
/* remove excess digits */
|
|
a->used -= b;
|
|
}
|
|
#endif
|