/* LibTomMath, multiple-precision integer library -- Tom St Denis
*
* LibTomMath is a library that provides multiple-precision
* integer arithmetic as well as number theoretic functionality.
*
* The library was designed directly after the MPI library by
* Michael Fromberger but has been written from scratch with
* additional optimizations in place.
*
* The library is free for all purposes without any express
* guarantee it works.
*
* Tom St Denis, tomstdenis@iahu.ca, http://math.libtomcrypt.org
*/
#include <tommath.h>
/* shift left a certain amount of digits */
int mp_lshd (mp_int * a, int b)
{
int x, res;
/* if its less than zero return */
if (b <= 0) {
return MP_OKAY;
}
/* grow to fit the new digits */
if (a->alloc < a->used + b) {
if ((res = mp_grow (a, a->used + b)) != MP_OKAY) {
return res;
}
}
{
register mp_digit *top, *bottom;
/* 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;
}
