view libtommath/bn_mp_expt_d.c @ 709:abd99ecd7ec2

use an empty writebuf rather than a NULL one
author Matt Johnston Wed, 20 Mar 2013 22:31:07 +0800 5ff8218bcee9 60fc6476e044
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#include <tommath.h>
#ifdef BN_MP_EXPT_D_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
*/

/* calculate c = a**b  using a square-multiply algorithm */
int mp_expt_d (mp_int * a, mp_digit b, mp_int * c)
{
int     res, x;
mp_int  g;

if ((res = mp_init_copy (&g, a)) != MP_OKAY) {
return res;
}

/* set initial result */
mp_set (c, 1);

for (x = 0; x < (int) DIGIT_BIT; x++) {
/* square */
if ((res = mp_sqr (c, c)) != MP_OKAY) {
mp_clear (&g);
return res;
}

/* if the bit is set multiply */
if ((b & (mp_digit) (((mp_digit)1) << (DIGIT_BIT - 1))) != 0) {
if ((res = mp_mul (c, &g, c)) != MP_OKAY) {
mp_clear (&g);
return res;
}
}

/* shift to next bit */
b <<= 1;
}

mp_clear (&g);
return MP_OKAY;
}
#endif

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