### view libtommath/bn_mp_div_2d.c @ 389:5ff8218bcee9

author Matt Johnston Thu, 11 Jan 2007 03:14:55 +0000 eed26cff980b 60fc6476e044
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```#include <tommath.h>
#ifdef BN_MP_DIV_2D_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
*/

/* shift right by a certain bit count (store quotient in c, optional remainder in d) */
int mp_div_2d (mp_int * a, int b, mp_int * c, mp_int * d)
{
mp_digit D, r, rr;
int     x, res;
mp_int  t;

/* if the shift count is <= 0 then we do no work */
if (b <= 0) {
res = mp_copy (a, c);
if (d != NULL) {
mp_zero (d);
}
return res;
}

if ((res = mp_init (&t)) != MP_OKAY) {
return res;
}

/* get the remainder */
if (d != NULL) {
if ((res = mp_mod_2d (a, b, &t)) != MP_OKAY) {
mp_clear (&t);
return res;
}
}

/* copy */
if ((res = mp_copy (a, c)) != MP_OKAY) {
mp_clear (&t);
return res;
}

/* shift by as many digits in the bit count */
if (b >= (int)DIGIT_BIT) {
mp_rshd (c, b / DIGIT_BIT);
}

/* shift any bit count < DIGIT_BIT */
D = (mp_digit) (b % DIGIT_BIT);
if (D != 0) {

mask = (((mp_digit)1) << D) - 1;

/* shift for lsb */
shift = DIGIT_BIT - D;

/* alias */
tmpc = c->dp + (c->used - 1);

/* carry */
r = 0;
for (x = c->used - 1; x >= 0; x--) {
/* get the lower  bits of this word in a temp */

/* shift the current word and mix in the carry bits from the previous word */
*tmpc = (*tmpc >> D) | (r << shift);
--tmpc;

/* set the carry to the carry bits of the current word found above */
r = rr;
}
}
mp_clamp (c);
if (d != NULL) {
mp_exch (&t, d);
}
mp_clear (&t);
return MP_OKAY;
}
#endif

/* \$Source: /cvs/libtom/libtommath/bn_mp_div_2d.c,v \$ */
/* \$Revision: 1.3 \$ */
/* \$Date: 2006/03/31 14:18:44 \$ */
```