X-Git-Url: https://git.distorted.org.uk/u/mdw/catacomb/blobdiff_plain/ba6e6b64033b1f9de49feccb5c9cd438354481f7..0f00dc4c8eb47e67bc0f148c2dd109f73a451e0a:/mpbarrett.c

diff --git a/mpbarrett.c b/mpbarrett.c
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-/* -*-c-*-
- *
- * $Id$
- *
- * Barrett modular reduction
- *
- * (c) 1999 Straylight/Edgeware
- */
-
-/*----- Licensing notice --------------------------------------------------*
- *
- * This file is part of Catacomb.
- *
- * Catacomb is free software; you can redistribute it and/or modify
- * 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.
- */
-
-/*----- Header files ------------------------------------------------------*/
-
-#include "mp.h"
-#include "mpbarrett.h"
-
-/*----- Main code ---------------------------------------------------------*/
-
-/* --- @mpbarrett_create@ --- *
- *
- * Arguments:	@mpbarrett *mb@ = pointer to Barrett reduction context
- *		@mp *m@ = modulus to work to
- *
- *
- * Returns:	Zero on success, nonzero on error.
- *
- * Use:		Initializes a Barrett reduction context ready for use.
- */
-
-int mpbarrett_create(mpbarrett *mb, mp *m)
-{
-  mp *b;
-
-  /* --- Validate the arguments --- */
-
-  if (!MP_POSP(m))
-    return (-1);
-
-  /* --- Compute %$\mu$% --- */
-
-  mp_shrink(m);
-  mb->k = MP_LEN(m);
-  mb->m = MP_COPY(m);
-  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@ --- *
- *
- * Arguments:	@mpbarrett *mb@ = pointer to Barrett reduction context
- *
- * Returns:	---
- *
- * Use:		Destroys a Barrett reduction context releasing any resources
- *		claimed.
- */
-
-void mpbarrett_destroy(mpbarrett *mb)
-{
-  mp_drop(mb->m);
-  mp_drop(mb->mu);
-}
-
-/* --- @mpbarrett_reduce@ --- *
- *
- * Arguments:	@mpbarrett *mb@ = pointer to Barrett reduction context
- *		@mp *d@ = destination for result
- *		@mp *m@ = number to reduce
- *
- * Returns:	The residue of @m@ modulo the number in the reduction
- *		context.
- *
- * Use:		Performs an efficient modular reduction.
- */
-
-mp *mpbarrett_reduce(mpbarrett *mb, mp *d, mp *m)
-{
-  mp *q;
-  size_t k = mb->k;
-
-  /* --- Special case if @m@ is too small --- */
-
-  if (MP_LEN(m) < k) {
-    m = MP_COPY(m);
-    if (d)
-      MP_DROP(d);
-    return (m);
-  }
-
-  /* --- First stage --- */
-
-  {
-    mp qq;
-    mp_build(&qq, m->v + (k - 1), m->vl);
-    q = mp_mul(MP_NEW, &qq, mb->mu);
-    if (MP_LEN(q) <= k) {
-      m = MP_COPY(m);
-      if (d)
-	MP_DROP(d);
-      MP_DROP(q);
-      return (m);
-    }
-  }
-
-  /* --- Second stage --- */
-
-  {
-    mp *r;
-    mpw *mvl;
-
-    MP_COPY(m);
-    if (MP_LEN(m) <= k + 1)
-      mvl = m->vl;
-    else
-      mvl = m->v + 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 | MP_NEG);
-    MP_DROP(r);
-    MP_DROP(q);
-    MP_DROP(m);
-  }
-
-  /* --- Final stage --- */
-
-  MP_SHRINK(d);
-  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);
-
-  /* --- Fix up the sign --- */
-
-  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_SHRINK(d);
-  return (d);
-}
-
-/*----- Test rig ----------------------------------------------------------*/
-
-#ifdef TEST_RIG
-
-static int vmod(dstr *v)
-{
-  mp *x = *(mp **)v[0].buf;
-  mp *n = *(mp **)v[1].buf;
-  mp *r = *(mp **)v[2].buf;
-  mp *s;
-  mpbarrett mb;
-  int ok = 1;
-
-  mpbarrett_create(&mb, n);
-  s = mpbarrett_reduce(&mb, MP_NEW, x);
-
-  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);
-    fputs("r = ", stderr); mp_writefile(r, stderr, 10); fputc('\n', stderr);
-    fputs("s = ", stderr); mp_writefile(s, stderr, 10); fputc('\n', stderr);
-    ok = 0;
-  }
-
-  mpbarrett_destroy(&mb);
-  mp_drop(x);
-  mp_drop(n);
-  mp_drop(r);
-  mp_drop(s);
-  assert(mparena_count(MPARENA_GLOBAL) == 0);
-  return (ok);
-}
-
-static test_chunk tests[] = {
-  { "mpbarrett-reduce", vmod, { &type_mp, &type_mp, &type_mp, 0 } },
-  { 0, 0, { 0 } }
-};
-
-int main(int argc, char *argv[])
-{
-  sub_init();
-  test_run(argc, argv, tests, SRCDIR "/tests/mpbarrett");
-  return (0);
-}
-
-#endif
-
-/*----- That's all, folks -------------------------------------------------*/