h1-mod/deps/libtommath/mp_lshd.c
2024-03-07 00:54:32 -05:00

43 lines
984 B
C

#include "tommath_private.h"
#ifdef 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)
{
mp_err err;
int x;
/* if its less than zero return */
if (b <= 0) {
return MP_OKAY;
}
/* no need to shift 0 around */
if (mp_iszero(a)) {
return MP_OKAY;
}
/* grow to fit the new digits */
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;
/* much like mp_rshd this is implemented using a sliding window
* except the window goes the other way around. Copying from
* the bottom to the top. see mp_rshd.c for more info.
*/
for (x = a->used; x --> b;) {
a->dp[x] = a->dp[x - b];
}
/* zero the lower digits */
s_mp_zero_digs(a->dp, b);
return MP_OKAY;
}
#endif