view libtommath/bn_mp_div_2.c @ 487:2e17f82a7330

Add multihop 'onion-forwarding' mode. Needs refinement, works.
author Matt Johnston Thu, 18 Sep 2008 14:47:02 +0000 5ff8218bcee9 60fc6476e044
line wrap: on
line source
```#include <tommath.h>
#ifdef BN_MP_DIV_2_C
/* 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
*
* The library is free for all purposes without any express
* guarantee it works.
*
* Tom St Denis, [email protected], http://math.libtomcrypt.com
*/

/* b = a/2 */
int mp_div_2(mp_int * a, mp_int * b)
{
int     x, res, oldused;

/* copy */
if (b->alloc < a->used) {
if ((res = mp_grow (b, a->used)) != MP_OKAY) {
return res;
}
}

oldused = b->used;
b->used = a->used;
{
register mp_digit r, rr, *tmpa, *tmpb;

/* source alias */
tmpa = a->dp + b->used - 1;

/* dest alias */
tmpb = b->dp + b->used - 1;

/* carry */
r = 0;
for (x = b->used - 1; x >= 0; x--) {
/* get the carry for the next iteration */
rr = *tmpa & 1;

/* shift the current digit, add in carry and store */
*tmpb-- = (*tmpa-- >> 1) | (r << (DIGIT_BIT - 1));

/* forward carry to next iteration */
r = rr;
}

/* zero excess digits */
tmpb = b->dp + b->used;
for (x = b->used; x < oldused; x++) {
*tmpb++ = 0;
}
}
b->sign = a->sign;
mp_clamp (b);
return MP_OKAY;
}
#endif

/* \$Source: /cvs/libtom/libtommath/bn_mp_div_2.c,v \$ */
/* \$Revision: 1.3 \$ */
/* \$Date: 2006/03/31 14:18:44 \$ */
```