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#include "tommath_private.h"
#ifdef BN_MP_LSHD_C
/* LibTomMath, multiple-precision integer library -- Tom St Denis */
/* SPDX-License-Identifier: Unlicense */
/* shift left a certain amount of digits */
mp_err mp_lshd(mp_int *a, int b)
{
int x;
mp_err err;
mp_digit *top, *bottom;
/* if its less than zero return */
if (b <= 0) {
return MP_OKAY;
}
/* no need to shift 0 around */
if (MP_IS_ZERO(a)) {
return MP_OKAY;
}
/* grow to fit the new digits */
if (a->alloc < (a->used + b)) {
if ((err = mp_grow(a, a->used + b)) != MP_OKAY) {
return err;
}
}
/* increment the used by the shift amount then copy upwards */
a->used += b;
/* top */
top = a->dp + a->used - 1;
/* base */
bottom = (a->dp + a->used - 1) - b;
/* much like mp_rshd this is implemented using a sliding window
* except the window goes the otherway around. Copying from
* the bottom to the top. see bn_mp_rshd.c for more info.
*/
for (x = a->used - 1; x >= b; x--) {
*top-- = *bottom--;
}
/* zero the lower digits */
MP_ZERO_DIGITS(a->dp, b);
return MP_OKAY;
}
#endif
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