X-Git-Url: https://git.distorted.org.uk/u/mdw/catacomb/blobdiff_plain/21a7c4b1cffbf33a19e4cf421e29420187ed7a89..34e4f738bcba58e6d8c4cabbb0b3232a65b42a9d:/mpbarrett.c diff --git a/mpbarrett.c b/mpbarrett.c index e438d02..934097d 100644 --- a/mpbarrett.c +++ b/mpbarrett.c @@ -1,6 +1,6 @@ /* -*-c-*- * - * $Id: mpbarrett.c,v 1.1 1999/12/10 23:21:59 mdw Exp $ + * $Id: mpbarrett.c,v 1.9 2004/04/01 12:50:09 mdw Exp $ * * Barrett modular reduction * @@ -30,6 +30,38 @@ /*----- Revision history --------------------------------------------------* * * $Log: mpbarrett.c,v $ + * Revision 1.9 2004/04/01 12:50:09 mdw + * Add cyclic group abstraction, with test code. Separate off exponentation + * functions for better static linking. Fix a buttload of bugs on the way. + * Generally ensure that negative exponents do inversion correctly. Add + * table of standard prime-field subgroups. (Binary field subgroups are + * currently unimplemented but easy to add if anyone ever finds a good one.) + * + * Revision 1.8 2001/06/16 13:00:20 mdw + * Use the generic exponentiation functions. + * + * Revision 1.7 2001/04/19 18:25:26 mdw + * Use sliding-window exponentiation. + * + * Revision 1.6 2000/10/08 12:03:44 mdw + * (mpbarrett_reduce): Cope with negative numbers. + * + * Revision 1.5 2000/07/29 17:04:33 mdw + * Change to use left-to-right bitwise exponentiation. This will improve + * performance when the base is small. + * + * Revision 1.4 2000/06/17 11:45:09 mdw + * Major memory management overhaul. Added arena support. Use the secure + * arena for secret integers. Replace and improve the MP management macros + * (e.g., replace MP_MODIFY by MP_DEST). + * + * Revision 1.3 1999/12/12 15:08:52 mdw + * Don't bother shifting %$q$% in @mpbarrett_reduce@, just skip the least + * significant digits. + * + * 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. * @@ -66,7 +98,9 @@ void mpbarrett_create(mpbarrett *mb, mp *m) mp_shrink(m); mb->k = MP_LEN(m); mb->m = MP_COPY(m); - b = mp_lsl(MP_NEW, MP_ONE, 2 * MPW_BITS * mb->k); + 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; } @@ -96,8 +130,7 @@ 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) @@ -109,7 +142,8 @@ 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); } @@ -119,7 +153,12 @@ 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); + return (m); + } } /* --- Second stage --- */ @@ -133,12 +172,11 @@ 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); 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); @@ -150,55 +188,15 @@ 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 ----------------------------------------------------------*/ @@ -217,7 +215,7 @@ 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); @@ -235,44 +233,8 @@ 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 } } };