### view libtommath/bn_mp_karatsuba_sqr.c @ 763:f744321ac048ecc

ecdh works against OpenSSH
author Matt Johnston Mon, 08 Apr 2013 23:12:20 +0800 5ff8218bcee9 60fc6476e044
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```#include <tommath.h>
#ifdef BN_MP_KARATSUBA_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
*/

/* Karatsuba squaring, computes b = a*a using three
* half size squarings
*
* See comments of karatsuba_mul for details.  It
* is essentially the same algorithm but merely
* tuned to perform recursive squarings.
*/
int mp_karatsuba_sqr (mp_int * a, mp_int * b)
{
mp_int  x0, x1, t1, t2, x0x0, x1x1;
int     B, err;

err = MP_MEM;

/* min # of digits */
B = a->used;

/* now divide in two */
B = B >> 1;

/* init copy all the temps */
if (mp_init_size (&x0, B) != MP_OKAY)
goto ERR;
if (mp_init_size (&x1, a->used - B) != MP_OKAY)
goto X0;

/* init temps */
if (mp_init_size (&t1, a->used * 2) != MP_OKAY)
goto X1;
if (mp_init_size (&t2, a->used * 2) != MP_OKAY)
goto T1;
if (mp_init_size (&x0x0, B * 2) != MP_OKAY)
goto T2;
if (mp_init_size (&x1x1, (a->used - B) * 2) != MP_OKAY)
goto X0X0;

{
register int x;
register mp_digit *dst, *src;

src = a->dp;

/* now shift the digits */
dst = x0.dp;
for (x = 0; x < B; x++) {
*dst++ = *src++;
}

dst = x1.dp;
for (x = B; x < a->used; x++) {
*dst++ = *src++;
}
}

x0.used = B;
x1.used = a->used - B;

mp_clamp (&x0);

/* now calc the products x0*x0 and x1*x1 */
if (mp_sqr (&x0, &x0x0) != MP_OKAY)
goto X1X1;           /* x0x0 = x0*x0 */
if (mp_sqr (&x1, &x1x1) != MP_OKAY)
goto X1X1;           /* x1x1 = x1*x1 */

/* now calc (x1+x0)**2 */
if (s_mp_add (&x1, &x0, &t1) != MP_OKAY)
goto X1X1;           /* t1 = x1 - x0 */
if (mp_sqr (&t1, &t1) != MP_OKAY)
goto X1X1;           /* t1 = (x1 - x0) * (x1 - x0) */

if (s_mp_add (&x0x0, &x1x1, &t2) != MP_OKAY)
goto X1X1;           /* t2 = x0x0 + x1x1 */
if (s_mp_sub (&t1, &t2, &t1) != MP_OKAY)
goto X1X1;           /* t1 = (x1+x0)**2 - (x0x0 + x1x1) */

/* shift by B */
if (mp_lshd (&t1, B) != MP_OKAY)
goto X1X1;           /* t1 = (x0x0 + x1x1 - (x1-x0)*(x1-x0))<<B */
if (mp_lshd (&x1x1, B * 2) != MP_OKAY)
goto X1X1;           /* x1x1 = x1x1 << 2*B */

if (mp_add (&x0x0, &t1, &t1) != MP_OKAY)
goto X1X1;           /* t1 = x0x0 + t1 */
if (mp_add (&t1, &x1x1, b) != MP_OKAY)
goto X1X1;           /* t1 = x0x0 + t1 + x1x1 */

err = MP_OKAY;

X1X1:mp_clear (&x1x1);
X0X0:mp_clear (&x0x0);
T2:mp_clear (&t2);
T1:mp_clear (&t1);
X1:mp_clear (&x1);
X0:mp_clear (&x0);
ERR:
return err;
}
#endif

/* \$Source: /cvs/libtom/libtommath/bn_mp_karatsuba_sqr.c,v \$ */
/* \$Revision: 1.5 \$ */
/* \$Date: 2006/03/31 14:18:44 \$ */
```