tommath/bn_mp_mul_2d.c

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/* 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.
*
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* Tom St Denis, tomstdenis@iahu.ca, http://math.libtomcrypt.org
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*/
#include <tommath.h>
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/* NOTE: This routine requires updating. For instance the c->used = c->alloc bit
is wrong. We should just shift c->used digits then set the carry as c->dp[c->used] = carry
To be fixed for LTM 0.18
*/
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/* shift left by a certain bit count */
int
mp_mul_2d (mp_int * a, int b, mp_int * c)
{
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mp_digit d;
int res;
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/* copy */
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if (a != c) {
if ((res = mp_copy (a, c)) != MP_OKAY) {
return res;
}
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}
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if (c->alloc < (int)(c->used + b/DIGIT_BIT + 2)) {
if ((res = mp_grow (c, c->used + b / DIGIT_BIT + 2)) != MP_OKAY) {
return res;
}
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}
/* shift by as many digits in the bit count */
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if (b >= (int)DIGIT_BIT) {
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if ((res = mp_lshd (c, b / DIGIT_BIT)) != MP_OKAY) {
return res;
}
}
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c->used = c->alloc;
/* shift any bit count < DIGIT_BIT */
d = (mp_digit) (b % DIGIT_BIT);
if (d != 0) {
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register mp_digit *tmpc, mask, r, rr;
register int x;
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/* bitmask for carries */
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mask = (((mp_digit)1) << d) - 1;
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/* alias */
tmpc = c->dp;
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/* carry */
r = 0;
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for (x = 0; x < c->used; x++) {
/* get the higher bits of the current word */
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rr = (*tmpc >> (DIGIT_BIT - d)) & mask;
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/* shift the current word and OR in the carry */
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*tmpc = ((*tmpc << d) | r) & MP_MASK;
++tmpc;
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/* set the carry to the carry bits of the current word */
r = rr;
}
}
mp_clamp (c);
return MP_OKAY;
}