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#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
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