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/* mpn_cnd_add_n -- Compute R = U + V if CND != 0 or R = U if CND == 0.
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Both cases should take the same time and perform the exact same memory
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accesses, since this function is intended to be used where side-channel
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attack resilience is relevant.
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Copyright 1992-1994, 1996, 2000, 2002, 2008, 2009, 2011, 2013 Free Software
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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.h"
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#include "gmp-impl.h"
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mp_limb_t
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mpn_cnd_add_n (mp_limb_t cnd, mp_ptr rp, mp_srcptr up, mp_srcptr vp, mp_size_t n)
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{
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mp_limb_t ul, vl, sl, rl, cy, cy1, cy2, mask;
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ASSERT (n >= 1);
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ASSERT (MPN_SAME_OR_SEPARATE_P (rp, up, n));
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ASSERT (MPN_SAME_OR_SEPARATE_P (rp, vp, n));
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mask = -(mp_limb_t) (cnd != 0);
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cy = 0;
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do
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{
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ul = *up++;
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vl = *vp++ & mask;
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#if GMP_NAIL_BITS == 0
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sl = ul + vl;
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cy1 = sl < ul;
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rl = sl + cy;
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cy2 = rl < sl;
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cy = cy1 | cy2;
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*rp++ = rl;
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#else
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rl = ul + vl;
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rl += cy;
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cy = rl >> GMP_NUMB_BITS;
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*rp++ = rl & GMP_NUMB_MASK;
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#endif
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}
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while (--n != 0);
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return cy;
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}
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