102 lines
2.2 KiB
C
102 lines
2.2 KiB
C
#include <tommath.h>
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#ifdef BN_MP_BALANCE_MUL_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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/* c = |a| * |b| using balancing multiplication.
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* If |a| is much less than |b|,
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* we firstly split b into chunks such that length of each one is
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* roughly equal to that of |a|.
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*/
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int mp_balance_mul (mp_int * a, mp_int * b, mp_int * c)
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{
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/* the following algorithm is taken from
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* Ruby core; namely, function 'bigmul1_balance'
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* from 'bignum.c'
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*/
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mp_int t1, t2;
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long i, an, bn, r, n;
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int res, min, max;
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int err = MP_MEM;
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mp_digit *bds, *t1ds;
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an = a->used;
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bn = b->used;
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if ((res = mp_grow(c, an + bn)) != MP_OKAY) {
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return res;
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}
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if (mp_init_size(&t1, an) != MP_OKAY) {
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goto ERR;
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}
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bds = b->dp;
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t1ds = t1.dp;
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n = 0;
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mp_int x;
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c->used = an + bn;
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while (bn > 0) {
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r = MIN(an, bn);
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for (i = 0; i < r; ++i)
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t1ds[i] = bds[n + i];
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t1.used = r;
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mp_init_size(&t2, an + r);
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mp_mul(a, &t1, &t2);
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if (t2.used > c->used - n) {
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min = c->used - n; max = t2.used;
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x.used = t2.used; x.dp = t2.dp;
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} else {
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min = t2.used; max = c->used - n;
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x.used = c->used - n; x.dp = c->dp + n;
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}
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register mp_digit u, *tmpx, *tmpt2, *tmpcn;
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register int j;
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tmpx = tmpcn = x.dp; tmpt2 = t2.dp;
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u = 0;
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for (j = 0; j < min; j++) {
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*tmpcn = *tmpx++ + *tmpt2++ + u;
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u = *tmpcn >> ((mp_digit)DIGIT_BIT);
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*tmpcn++ &= MP_MASK;
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}
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if (min != max) {
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for (; j < max; j++) {
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*tmpcn = x.dp[j] + u;
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u = *tmpcn >> ((mp_digit)DIGIT_BIT);
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*tmpcn++ &= MP_MASK;
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}
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}
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*tmpcn++ = u;
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bn -= r;
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n += r;
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}
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mp_clamp(c);
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return MP_OKAY;
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ERR:
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return err;
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}
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#endif
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/* $Source$ */
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/* $Revision$ */
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/* $Date$ */
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