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67 lines
1.9 KiB
C
67 lines
1.9 KiB
C
/* mpn_redc_n. Set cp[] <- up[]/R^n mod mp[]. Clobber up[].
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mp[] is n limbs; up[] is 2n limbs, the inverse ip[] is n limbs.
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THIS IS AN INTERNAL FUNCTION WITH A MUTABLE INTERFACE. IT IS ONLY
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SAFE TO REACH THIS FUNCTION THROUGH DOCUMENTED INTERFACES.
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Copyright (C) 2009 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 the GNU Lesser General Public License as published by
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the Free Software Foundation; either version 3 of the License, or (at your
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option) any later version.
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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 Lesser General Public
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License for more details.
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You should have received a copy of the GNU Lesser General Public License
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along with the GNU MP Library. If not, see http://www.gnu.org/licenses/. */
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#include "gmp.h"
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#include "gmp-impl.h"
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/*
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TODO
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* We assume mpn_mulmod_bnm1 is always faster than plain mpn_mul_n (or a
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future mpn_mulhi) for the range we will be called. Follow up that
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assumption.
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* Decrease scratch usage.
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*/
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void
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mpn_redc_n (mp_ptr rp, mp_ptr up, mp_srcptr mp, mp_size_t n, mp_srcptr ip)
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{
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mp_ptr xp, yp, scratch;
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mp_limb_t cy;
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mp_size_t rn;
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TMP_DECL;
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TMP_MARK;
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rn = mpn_mulmod_bnm1_next_size (n);
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scratch = TMP_ALLOC_LIMBS (n + rn + mpn_mulmod_bnm1_itch (rn, n, n));
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xp = scratch;
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mpn_mullo_n (xp, up, ip, n);
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yp = scratch + n;
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mpn_mulmod_bnm1 (yp, rn, xp, n, mp, n, scratch + n + rn);
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ASSERT_ALWAYS (2 * n > rn); /* could handle this */
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cy = mpn_sub_n (yp + rn, yp, up, 2*n - rn); /* undo wrap around */
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MPN_DECR_U (yp + 2*n - rn, rn, cy);
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cy = mpn_sub_n (rp, up + n, yp + n, n);
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if (cy != 0)
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mpn_add_n (rp, rp, mp, n);
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TMP_FREE;
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}
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