X-Git-Url: https://git.distorted.org.uk/u/mdw/catacomb/blobdiff_plain/ed6d1bd2f0cd07a49530968e33d43955f1a3c1ca..7280f7f44cfae62f6d34761ac88aa19da7da5dd8:/mpbarrett.c diff --git a/mpbarrett.c b/mpbarrett.c index 025d4e4..13210b3 100644 --- a/mpbarrett.c +++ b/mpbarrett.c @@ -1,13 +1,13 @@ /* -*-c-*- * - * $Id: mpbarrett.c,v 1.2 1999/12/11 01:50:56 mdw Exp $ + * $Id$ * * Barrett modular reduction * * (c) 1999 Straylight/Edgeware */ -/*----- Licensing notice --------------------------------------------------* +/*----- Licensing notice --------------------------------------------------* * * This file is part of Catacomb. * @@ -15,29 +15,18 @@ * it under the terms of the GNU Library General Public License as * published by the Free Software Foundation; either version 2 of the * License, or (at your option) any later version. - * + * * Catacomb is distributed in the hope that it will be useful, * but WITHOUT ANY WARRANTY; without even the implied warranty of * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the * GNU Library General Public License for more details. - * + * * You should have received a copy of the GNU Library General Public * License along with Catacomb; if not, write to the Free * Software Foundation, Inc., 59 Temple Place - Suite 330, Boston, * MA 02111-1307, USA. */ -/*----- Revision history --------------------------------------------------* - * - * $Log: mpbarrett.c,v $ - * Revision 1.2 1999/12/11 01:50:56 mdw - * Improve initialization slightly. - * - * Revision 1.1 1999/12/10 23:21:59 mdw - * Barrett reduction support: works with even moduli. - * - */ - /*----- Header files ------------------------------------------------------*/ #include "mp.h" @@ -51,29 +40,31 @@ * @mp *m@ = modulus to work to * * - * Returns: --- + * Returns: Zero on success, nonzero on error. * * Use: Initializes a Barrett reduction context ready for use. */ -void mpbarrett_create(mpbarrett *mb, mp *m) +int mpbarrett_create(mpbarrett *mb, mp *m) { mp *b; /* --- Validate the arguments --- */ - assert(((void)"Barrett modulus must be positive", (m->f & MP_NEG) == 0)); + if (!MP_POSP(m)) + return (-1); /* --- Compute %$\mu$% --- */ mp_shrink(m); mb->k = MP_LEN(m); mb->m = MP_COPY(m); - b = mp_create(2 * mb->k + 1); + b = mp_new(2 * mb->k + 1, 0); MPX_ZERO(b->v, b->vl - 1); b->vl[-1] = 1; mp_div(&b, 0, b, m); mb->mu = b; + return (0); } /* --- @mpbarrett_destroy@ --- * @@ -101,8 +92,7 @@ void mpbarrett_destroy(mpbarrett *mb) * Returns: The residue of @m@ modulo the number in the reduction * context. * - * Use: Performs an efficient modular reduction. The argument is - * assumed to be positive. + * Use: Performs an efficient modular reduction. */ mp *mpbarrett_reduce(mpbarrett *mb, mp *d, mp *m) @@ -114,7 +104,8 @@ mp *mpbarrett_reduce(mpbarrett *mb, mp *d, mp *m) if (MP_LEN(m) < k) { m = MP_COPY(m); - MP_DROP(d); + if (d) + MP_DROP(d); return (m); } @@ -124,7 +115,13 @@ mp *mpbarrett_reduce(mpbarrett *mb, mp *d, mp *m) mp qq; mp_build(&qq, m->v + (k - 1), m->vl); q = mp_mul(MP_NEW, &qq, mb->mu); - q = mp_lsr(q, q, MPW_BITS * (k + 1)); + if (MP_LEN(q) <= k) { + m = MP_COPY(m); + if (d) + MP_DROP(d); + MP_DROP(q); + return (m); + } } /* --- Second stage --- */ @@ -138,12 +135,11 @@ mp *mpbarrett_reduce(mpbarrett *mb, mp *d, mp *m) mvl = m->vl; else mvl = m->v + k + 1; - r = mp_create(k + 1); - mpx_umul(r->v, r->vl, q->v, q->vl, mb->m->v, mb->m->vl); - r->f = (q->f | mb->m->f) & MP_BURN; - MP_MODIFY(d, k + 1); + r = mp_new(k + 1, (q->f | mb->m->f) & MP_BURN); + mpx_umul(r->v, r->vl, q->v + k + 1, q->vl, mb->m->v, mb->m->vl); + MP_DEST(d, k + 1, r->f | MP_UNDEF); mpx_usub(d->v, d->vl, m->v, mvl, r->v, r->vl); - d->f = (m->f | r->f) & MP_BURN; + d->f = (m->f | r->f) & (MP_BURN | MP_NEG); MP_DROP(r); MP_DROP(q); MP_DROP(m); @@ -155,55 +151,15 @@ mp *mpbarrett_reduce(mpbarrett *mb, mp *d, mp *m) while (MPX_UCMP(d->v, d->vl, >=, mb->m->v, mb->m->vl)) mpx_usub(d->v, d->vl, d->v, d->vl, mb->m->v, mb->m->vl); - MP_SHRINK(d); - return (d); -} - -/* --- @mpbarrett_exp@ --- * - * - * Arguments: @mpbarrett *mb@ = pointer to Barrett reduction context - * @mp *d@ = fake destination - * @mp *a@ = base - * @mp *e@ = exponent - * - * Returns: Result, %$a^e \bmod m$%. - */ + /* --- Fix up the sign --- */ -mp *mpbarrett_exp(mpbarrett *mb, mp *d, mp *a, mp *e) -{ - mpscan sc; - mp *x = MP_ONE; - mp *spare = MP_NEW; - - a = MP_COPY(a); - mp_scan(&sc, e); - if (MP_STEP(&sc)) { - size_t sq = 0; - for (;;) { - mp *dd; - if (MP_BIT(&sc)) { - while (sq) { - dd = mp_sqr(spare, a); - dd = mpbarrett_reduce(mb, dd, dd); - spare = a; a = dd; - sq--; - } - dd = mp_mul(spare, x, a); - dd = mpbarrett_reduce(mb, dd, dd); - spare = x; x = dd; - } - sq++; - if (!MP_STEP(&sc)) - break; - } + if (d->f & MP_NEG) { + mpx_usub(d->v, d->vl, mb->m->v, mb->m->vl, d->v, d->vl); + d->f &= ~MP_NEG; } - MP_DROP(a); - if (spare != MP_NEW) - MP_DROP(spare); - if (d != MP_NEW) - MP_DROP(d); - return (x); + MP_SHRINK(d); + return (d); } /*----- Test rig ----------------------------------------------------------*/ @@ -222,7 +178,7 @@ static int vmod(dstr *v) mpbarrett_create(&mb, n); s = mpbarrett_reduce(&mb, MP_NEW, x); - if (MP_CMP(s, !=, r)) { + if (!MP_EQ(s, r)) { fputs("\n*** barrett reduction failure\n", stderr); fputs("x = ", stderr); mp_writefile(x, stderr, 10); fputc('\n', stderr); fputs("n = ", stderr); mp_writefile(n, stderr, 10); fputc('\n', stderr); @@ -240,44 +196,8 @@ static int vmod(dstr *v) return (ok); } -static int vexp(dstr *v) -{ - mp *m = *(mp **)v[0].buf; - mp *a = *(mp **)v[1].buf; - mp *b = *(mp **)v[2].buf; - mp *r = *(mp **)v[3].buf; - mp *mr; - int ok = 1; - - mpbarrett mb; - mpbarrett_create(&mb, m); - - mr = mpbarrett_exp(&mb, MP_NEW, a, b); - - if (MP_CMP(mr, !=, r)) { - fputs("\n*** barrett modexp failed", stderr); - fputs("\n m = ", stderr); mp_writefile(m, stderr, 10); - fputs("\n a = ", stderr); mp_writefile(a, stderr, 10); - fputs("\n e = ", stderr); mp_writefile(b, stderr, 10); - fputs("\n r = ", stderr); mp_writefile(r, stderr, 10); - fputs("\nmr = ", stderr); mp_writefile(mr, stderr, 10); - fputc('\n', stderr); - ok = 0; - } - - mp_drop(m); - mp_drop(a); - mp_drop(b); - mp_drop(r); - mp_drop(mr); - mpbarrett_destroy(&mb); - assert(mparena_count(MPARENA_GLOBAL) == 0); - return ok; -} - static test_chunk tests[] = { { "mpbarrett-reduce", vmod, { &type_mp, &type_mp, &type_mp, 0 } }, - { "mpbarrett-exp", vexp, { &type_mp, &type_mp, &type_mp, &type_mp, 0 } }, { 0, 0, { 0 } } };