85 lines
2.3 KiB
C
85 lines
2.3 KiB
C
#include <tommath.h>
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#ifdef BN_S_MP_SQR_C
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/* LibTomMath, multiple-precision integer library -- Tom St Denis
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*
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* LibTomMath is a library that provides multiple-precision
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* integer arithmetic as well as number theoretic functionality.
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*
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* The library was designed directly after the MPI library by
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* Michael Fromberger but has been written from scratch with
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* additional optimizations in place.
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*
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* The library is free for all purposes without any express
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* guarantee it works.
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*
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* Tom St Denis, tomstdenis@gmail.com, http://libtom.org
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*/
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/* low level squaring, b = a*a, HAC pp.596-597, Algorithm 14.16 */
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int s_mp_sqr (mp_int * a, mp_int * b)
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{
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mp_int t;
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int res, ix, iy, pa;
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mp_word r;
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mp_digit u, tmpx, *tmpt;
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pa = a->used;
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if ((res = mp_init_size (&t, 2*pa + 1)) != MP_OKAY) {
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return res;
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}
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/* default used is maximum possible size */
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t.used = 2*pa + 1;
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for (ix = 0; ix < pa; ix++) {
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/* first calculate the digit at 2*ix */
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/* calculate double precision result */
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r = ((mp_word) t.dp[2*ix]) +
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((mp_word)a->dp[ix])*((mp_word)a->dp[ix]);
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/* store lower part in result */
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t.dp[ix+ix] = (mp_digit) (r & ((mp_word) MP_MASK));
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/* get the carry */
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u = (mp_digit)(r >> ((mp_word) DIGIT_BIT));
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/* left hand side of A[ix] * A[iy] */
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tmpx = a->dp[ix];
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/* alias for where to store the results */
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tmpt = t.dp + (2*ix + 1);
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for (iy = ix + 1; iy < pa; iy++) {
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/* first calculate the product */
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r = ((mp_word)tmpx) * ((mp_word)a->dp[iy]);
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/* now calculate the double precision result, note we use
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* addition instead of *2 since it's easier to optimize
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*/
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r = ((mp_word) *tmpt) + r + r + ((mp_word) u);
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/* store lower part */
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*tmpt++ = (mp_digit) (r & ((mp_word) MP_MASK));
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/* get carry */
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u = (mp_digit)(r >> ((mp_word) DIGIT_BIT));
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}
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/* propagate upwards */
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while (u != ((mp_digit) 0)) {
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r = ((mp_word) *tmpt) + ((mp_word) u);
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*tmpt++ = (mp_digit) (r & ((mp_word) MP_MASK));
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u = (mp_digit)(r >> ((mp_word) DIGIT_BIT));
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}
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}
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mp_clamp (&t);
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mp_exch (&t, b);
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mp_clear (&t);
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return MP_OKAY;
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}
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#endif
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/* $Source: /cvs/libtom/libtommath/bn_s_mp_sqr.c,v $ */
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/* $Revision: 1.4 $ */
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/* $Date: 2006/12/28 01:25:13 $ */
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