55 lines
1.2 KiB
C
55 lines
1.2 KiB
C
#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 */
|
|
top = a->dp;
|
|
for (x = 0; x < b; x++) {
|
|
*top++ = 0;
|
|
}
|
|
|
|
return MP_OKAY;
|
|
}
|
|
#endif
|