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Change-Id: Iae65e95cfa0d92091b8b0a424ae36d88efa76aa9 Reviewed-on: https://review.haiku-os.org/c/buildtools/+/3020 Reviewed-by: Adrien Destugues <pulkomandy@gmail.com>
132 lines
3.9 KiB
C
132 lines
3.9 KiB
C
/* mpn_trialdiv -- find small factors of an mpn number using trial division.
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Contributed to the GNU project by Torbjorn Granlund.
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THE FUNCTION IN THIS FILE IS INTERNAL WITH A MUTABLE INTERFACE. IT IS ONLY
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SAFE TO REACH IT THROUGH DOCUMENTED INTERFACES. IN FACT, IT IS ALMOST
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GUARANTEED THAT IT WILL CHANGE OR DISAPPEAR IN A FUTURE GNU MP RELEASE.
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Copyright 2009, 2010, 2012, 2013 Free Software Foundation, Inc.
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This file is part of the GNU MP Library.
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The GNU MP Library is free software; you can redistribute it and/or modify
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it under the terms of either:
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* the GNU Lesser General Public License as published by the Free
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Software Foundation; either version 3 of the License, or (at your
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option) any later version.
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or
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* the GNU General Public License as published by the Free Software
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Foundation; either version 2 of the License, or (at your option) any
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later version.
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or both in parallel, as here.
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The GNU MP Library is distributed in the hope that it will be useful, but
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WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
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or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
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for more details.
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You should have received copies of the GNU General Public License and the
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GNU Lesser General Public License along with the GNU MP Library. If not,
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see https://www.gnu.org/licenses/. */
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/*
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This function finds the first (smallest) factor represented in
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trialdivtab.h. It does not stop the factoring effort just because it has
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reached some sensible limit, such as the square root of the input number.
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The caller can limit the factoring effort by passing NPRIMES. The function
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will then divide until that limit, or perhaps a few primes more. A position
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which only mpn_trialdiv can make sense of is returned in the WHERE
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parameter. It can be used for restarting the factoring effort; the first
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call should pass 0 here.
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Input: 1. A non-negative number T = {tp,tn}
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2. NPRIMES as described above,
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3. *WHERE as described above.
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Output: 1. *WHERE updated as described above.
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2. Return value is non-zero if we found a factor, else zero
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To get the actual prime factor, compute the mod B inverse
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of the return value.
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*/
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#include "gmp-impl.h"
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struct gmp_primes_dtab {
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mp_limb_t binv;
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mp_limb_t lim;
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};
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struct gmp_primes_ptab {
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mp_limb_t ppp; /* primes, multiplied together */
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mp_limb_t cps[7]; /* ppp values pre-computed for mpn_mod_1s_4p */
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gmp_uint_least32_t idx:24; /* index of first primes in dtab */
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gmp_uint_least32_t np :8; /* number of primes related to this entry */
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};
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static const struct gmp_primes_dtab gmp_primes_dtab[] =
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{
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#define WANT_dtab
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#define P(p,inv,lim) {inv,lim}
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#include "trialdivtab.h"
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#undef WANT_dtab
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#undef P
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{0,0}
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};
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static const struct gmp_primes_ptab gmp_primes_ptab[] =
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{
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#define WANT_ptab
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#include "trialdivtab.h"
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#undef WANT_ptab
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};
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#define PTAB_LINES (sizeof (gmp_primes_ptab) / sizeof (gmp_primes_ptab[0]))
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/* FIXME: We could optimize out one of the outer loop conditions if we
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had a final ptab entry with a huge np field. */
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mp_limb_t
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mpn_trialdiv (mp_srcptr tp, mp_size_t tn, mp_size_t nprimes, int *where)
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{
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mp_limb_t ppp;
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const mp_limb_t *cps;
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const struct gmp_primes_dtab *dp;
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long i, j, idx, np;
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mp_limb_t r, q;
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ASSERT (tn >= 1);
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for (i = *where; i < PTAB_LINES; i++)
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{
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ppp = gmp_primes_ptab[i].ppp;
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cps = gmp_primes_ptab[i].cps;
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r = mpn_mod_1s_4p (tp, tn, ppp << cps[1], cps);
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idx = gmp_primes_ptab[i].idx;
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np = gmp_primes_ptab[i].np;
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/* Check divisibility by individual primes. */
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dp = &gmp_primes_dtab[idx] + np;
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for (j = -np; j < 0; j++)
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{
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q = r * dp[j].binv;
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if (q <= dp[j].lim)
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{
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*where = i;
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return dp[j].binv;
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}
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}
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nprimes -= np;
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if (nprimes <= 0)
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return 0;
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}
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return 0;
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}
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