### view libtommath/bn_s_mp_sqr.c @ 487:2e17f82a7330

Add multihop 'onion-forwarding' mode. Needs refinement, works.
author Matt Johnston Thu, 18 Sep 2008 14:47:02 +0000 5ff8218bcee9 60fc6476e044
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```#include <tommath.h>
#ifdef BN_S_MP_SQR_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
*/

/* low level squaring, b = a*a, HAC pp.596-597, Algorithm 14.16 */
int s_mp_sqr (mp_int * a, mp_int * b)
{
mp_int  t;
int     res, ix, iy, pa;
mp_word r;
mp_digit u, tmpx, *tmpt;

pa = a->used;
if ((res = mp_init_size (&t, 2*pa + 1)) != MP_OKAY) {
return res;
}

/* default used is maximum possible size */
t.used = 2*pa + 1;

for (ix = 0; ix < pa; ix++) {
/* first calculate the digit at 2*ix */
/* calculate double precision result */
r = ((mp_word) t.dp[2*ix]) +
((mp_word)a->dp[ix])*((mp_word)a->dp[ix]);

/* store lower part in result */
t.dp[ix+ix] = (mp_digit) (r & ((mp_word) MP_MASK));

/* get the carry */
u           = (mp_digit)(r >> ((mp_word) DIGIT_BIT));

/* left hand side of A[ix] * A[iy] */
tmpx        = a->dp[ix];

/* alias for where to store the results */
tmpt        = t.dp + (2*ix + 1);

for (iy = ix + 1; iy < pa; iy++) {
/* first calculate the product */
r       = ((mp_word)tmpx) * ((mp_word)a->dp[iy]);

/* now calculate the double precision result, note we use
*/
r       = ((mp_word) *tmpt) + r + r + ((mp_word) u);

/* store lower part */
*tmpt++ = (mp_digit) (r & ((mp_word) MP_MASK));

/* get carry */
u       = (mp_digit)(r >> ((mp_word) DIGIT_BIT));
}
/* propagate upwards */
while (u != ((mp_digit) 0)) {
r       = ((mp_word) *tmpt) + ((mp_word) u);
*tmpt++ = (mp_digit) (r & ((mp_word) MP_MASK));
u       = (mp_digit)(r >> ((mp_word) DIGIT_BIT));
}
}

mp_clamp (&t);
mp_exch (&t, b);
mp_clear (&t);
return MP_OKAY;
}
#endif

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