redc_n.c
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- /* mpn_redc_n. Set cp[] <- up[]/R^n mod mp[]. Clobber up[].
- mp[] is n limbs; up[] is 2n limbs, the inverse ip[] is n limbs.
- THIS IS AN INTERNAL FUNCTION WITH A MUTABLE INTERFACE. IT IS ONLY
- SAFE TO REACH THIS FUNCTION THROUGH DOCUMENTED INTERFACES.
- Copyright (C) 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"
- /*
- TODO
- * We assume mpn_mulmod_bnm1 is always faster than plain mpn_mul_n (or a
- future mpn_mulhi) for the range we will be called. Follow up that
- assumption.
- * Decrease scratch usage.
- */
- void
- mpn_redc_n (mp_ptr rp, mp_ptr up, mp_srcptr mp, mp_size_t n, mp_srcptr ip)
- {
- mp_ptr xp, yp, scratch;
- mp_limb_t cy;
- mp_size_t rn;
- TMP_DECL;
- TMP_MARK;
- rn = mpn_mulmod_bnm1_next_size (n);
- scratch = TMP_ALLOC_LIMBS (n + rn + mpn_mulmod_bnm1_itch (rn, n, n));
- xp = scratch;
- mpn_mullo_n (xp, up, ip, n);
- yp = scratch + n;
- mpn_mulmod_bnm1 (yp, rn, xp, n, mp, n, scratch + n + rn);
- ASSERT_ALWAYS (2 * n > rn); /* could handle this */
- cy = mpn_sub_n (yp + rn, yp, up, 2*n - rn); /* undo wrap around */
- MPN_DECR_U (yp + 2*n - rn, rn, cy);
- cy = mpn_sub_n (rp, up + n, yp + n, n);
- if (cy != 0)
- mpn_add_n (rp, rp, mp, n);
- TMP_FREE;
- }