Coverage Report

Created: 2025-03-06 07:58

/src/gmp/mpn/redc_n.c
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/* mpn_redc_n.  Set rp[] <- 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 2009, 2012 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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#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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  * Consider removing the residue canonicalisation.
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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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  ASSERT (n > 8);
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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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}