tommath/bn_s_mp_sqr.c

83 lines
2.3 KiB
C
Raw Normal View History

#include <tommath_private.h>
2004-10-29 18:07:18 -04:00
#ifdef BN_S_MP_SQR_C
2003-02-28 11:08:34 -05:00
/* LibTomMath, multiple-precision integer library -- Tom St Denis
*
2003-08-04 21:24:44 -04:00
* LibTomMath is a library that provides multiple-precision
2003-02-28 11:08:34 -05:00
* integer arithmetic as well as number theoretic functionality.
*
2003-08-04 21:24:44 -04:00
* The library was designed directly after the MPI library by
2003-02-28 11:08:34 -05:00
* Michael Fromberger but has been written from scratch with
* additional optimizations in place.
*
* The library is free for all purposes without any express
* guarantee it works.
*/
/* low level squaring, b = a*a, HAC pp.596-597, Algorithm 14.16 */
2017-09-20 10:59:43 -04:00
int s_mp_sqr(const mp_int *a, mp_int *b)
2003-02-28 11:08:34 -05:00
{
2017-08-30 13:15:27 -04:00
mp_int t;
int res, ix, iy, pa;
mp_word r;
mp_digit u, tmpx, *tmpt;
2003-02-28 11:08:34 -05:00
2017-08-30 13:15:27 -04:00
pa = a->used;
if ((res = mp_init_size(&t, (2 * pa) + 1)) != MP_OKAY) {
return res;
}
2004-04-11 16:46:22 -04:00
2017-08-30 13:15:27 -04:00
/* default used is maximum possible size */
t.used = (2 * pa) + 1;
2003-02-28 11:08:34 -05:00
2017-08-30 13:15:27 -04:00
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]);
2003-02-28 11:08:34 -05:00
2017-08-30 13:15:27 -04:00
/* store lower part in result */
2017-10-15 13:58:35 -04:00
t.dp[ix+ix] = (mp_digit)(r & (mp_word)MP_MASK);
2003-02-28 11:08:34 -05:00
2017-08-30 13:15:27 -04:00
/* get the carry */
2017-10-15 13:58:35 -04:00
u = (mp_digit)(r >> (mp_word)DIGIT_BIT);
2003-02-28 11:08:34 -05:00
2017-08-30 13:15:27 -04:00
/* left hand side of A[ix] * A[iy] */
tmpx = a->dp[ix];
2003-02-28 11:08:34 -05:00
2017-08-30 13:15:27 -04:00
/* alias for where to store the results */
tmpt = t.dp + ((2 * ix) + 1);
2017-08-29 23:51:11 -04:00
2017-08-30 13:15:27 -04:00
for (iy = ix + 1; iy < pa; iy++) {
/* first calculate the product */
2017-10-15 13:58:35 -04:00
r = (mp_word)tmpx * (mp_word)a->dp[iy];
2003-02-28 11:08:34 -05:00
2017-08-30 13:15:27 -04:00
/* now calculate the double precision result, note we use
* addition instead of *2 since it's easier to optimize
*/
2017-10-15 13:58:35 -04:00
r = (mp_word)*tmpt + r + r + (mp_word)u;
2003-02-28 11:08:34 -05:00
2017-08-30 13:15:27 -04:00
/* store lower part */
2017-10-15 13:58:35 -04:00
*tmpt++ = (mp_digit)(r & (mp_word)MP_MASK);
2003-02-28 11:08:34 -05:00
2017-08-30 13:15:27 -04:00
/* get carry */
2017-10-15 13:58:35 -04:00
u = (mp_digit)(r >> (mp_word)DIGIT_BIT);
2017-08-30 13:15:27 -04:00
}
/* propagate upwards */
2017-10-15 13:57:12 -04:00
while (u != 0uL) {
2017-10-15 13:58:35 -04:00
r = (mp_word)*tmpt + (mp_word)u;
*tmpt++ = (mp_digit)(r & (mp_word)MP_MASK);
u = (mp_digit)(r >> (mp_word)DIGIT_BIT);
2017-08-30 13:15:27 -04:00
}
}
2003-02-28 11:08:34 -05:00
2017-08-30 13:15:27 -04:00
mp_clamp(&t);
mp_exch(&t, b);
mp_clear(&t);
return MP_OKAY;
2003-02-28 11:08:34 -05:00
}
2004-10-29 18:07:18 -04:00
#endif
2005-08-01 12:37:28 -04:00
2017-08-28 10:27:26 -04:00
/* ref: $Format:%D$ */
/* git commit: $Format:%H$ */
/* commit time: $Format:%ai$ */