tommath/bn_mp_mul_2d.c
2010-07-15 17:25:17 +02:00

60 lines
1.5 KiB
C

/* LibTomMath, multiple-precision integer library -- Tom St Denis
*
* LibTomMath is library that provides for multiple-precision
* integer arithmetic as well as number theoretic functionality.
*
* The library is 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 by a certain bit count */
int
mp_mul_2d (mp_int * a, int b, mp_int * c)
{
mp_digit d, r, rr;
int x, res;
/* copy */
if ((res = mp_copy (a, c)) != MP_OKAY) {
return res;
}
if ((res = mp_grow (c, c->used + b / DIGIT_BIT + 1)) != MP_OKAY) {
return res;
}
/* shift by as many digits in the bit count */
if (b >= DIGIT_BIT) {
if ((res = mp_lshd (c, b / DIGIT_BIT)) != MP_OKAY) {
return res;
}
}
c->used = c->alloc;
/* shift any bit count < DIGIT_BIT */
d = (mp_digit) (b % DIGIT_BIT);
if (d != 0) {
r = 0;
for (x = 0; x < c->used; x++) {
/* get the higher bits of the current word */
rr = (c->dp[x] >> (DIGIT_BIT - d)) & ((mp_digit) ((1U << d) - 1U));
/* shift the current word and OR in the carry */
c->dp[x] = ((c->dp[x] << d) | r) & MP_MASK;
/* set the carry to the carry bits of the current word */
r = rr;
}
}
mp_clamp (c);
return MP_OKAY;
}