### view libtommath/bn_mp_div_2.c @ 350:01e4180895ba

merge of '9a4e042fd565f46141e81e0c1ab90260303348fe' and 'bea3887a5875cf3ab8a1331e15e698b37b61fe37'
author Matt Johnston Mon, 07 Aug 2006 13:41:23 +0000 eed26cff980b 5ff8218bcee9
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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.org
*/

/* 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
```