mod_1_1.c
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- /* mpn_mod_1_1p (ap, n, b, cps)
- Divide (ap,,n) by b. Return the single-limb remainder.
- Contributed to the GNU project by Torbjorn Granlund.
- Based on a suggestion by Peter L. Montgomery.
- THE FUNCTIONS IN THIS FILE ARE INTERNAL WITH MUTABLE INTERFACES. IT IS ONLY
- SAFE TO REACH THEM THROUGH DOCUMENTED INTERFACES. IN FACT, IT IS ALMOST
- GUARANTEED THAT THEY WILL CHANGE OR DISAPPEAR IN A FUTURE GNU MP RELEASE.
- Copyright 2008, 2009 Free Software Foundation, Inc.
- This file is part of the GNU MP Library.
- The GNU MP Library is free software; you can redistribute it and/or modify
- it under the terms of the GNU Lesser General Public License as published by
- the Free Software Foundation; either version 3 of the License, or (at your
- option) any later version.
- The GNU MP Library 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 Lesser General Public
- License for more details.
- You should have received a copy of the GNU Lesser General Public License
- along with the GNU MP Library. If not, see http://www.gnu.org/licenses/. */
- #include "gmp.h"
- #include "gmp-impl.h"
- #include "longlong.h"
- void
- mpn_mod_1_1p_cps (mp_limb_t cps[4], mp_limb_t b)
- {
- mp_limb_t bi;
- mp_limb_t B1modb, B2modb;
- int cnt;
- count_leading_zeros (cnt, b);
- b <<= cnt;
- invert_limb (bi, b);
- if (UNLIKELY (cnt == 0))
- B1modb = -b;
- else
- B1modb = -b * ((bi >> (GMP_LIMB_BITS-cnt)) | (CNST_LIMB(1) << cnt));
- ASSERT (B1modb <= b); /* NB: not fully reduced mod b */
- udiv_rnd_preinv (B2modb, B1modb, b, bi);
- cps[0] = bi;
- cps[1] = cnt;
- cps[2] = B1modb >> cnt;
- cps[3] = B2modb >> cnt;
- }
- mp_limb_t
- mpn_mod_1_1p (mp_srcptr ap, mp_size_t n, mp_limb_t b, mp_limb_t bmodb[4])
- {
- mp_limb_t rh, rl, bi, q, ph, pl, r;
- mp_limb_t B1modb, B2modb;
- mp_size_t i;
- int cnt;
- mp_limb_t mask;
- ASSERT (n >= 2); /* fix tuneup.c if this is changed */
- B1modb = bmodb[2];
- B2modb = bmodb[3];
- umul_ppmm (ph, pl, ap[n - 1], B1modb);
- add_ssaaaa (rh, rl, ph, pl, 0, ap[n - 2]);
- for (i = n - 3; i >= 0; i -= 1)
- {
- /* rr = ap[i] < B
- + LO(rr) * (B mod b) <= (B-1)(b-1)
- + HI(rr) * (B^2 mod b) <= (B-1)(b-1)
- */
- umul_ppmm (ph, pl, rl, B1modb);
- add_ssaaaa (ph, pl, ph, pl, 0, ap[i]);
- umul_ppmm (rh, rl, rh, B2modb);
- add_ssaaaa (rh, rl, rh, rl, ph, pl);
- }
- bi = bmodb[0];
- cnt = bmodb[1];
- if (LIKELY (cnt != 0))
- rh = (rh << cnt) | (rl >> (GMP_LIMB_BITS - cnt));
- mask = -(mp_limb_t) (rh >= b);
- rh -= mask & b;
- udiv_qrnnd_preinv (q, r, rh, rl << cnt, b, bi);
- return r >> cnt;
- }