112 lines
3.2 KiB
C
112 lines
3.2 KiB
C
/*=============================================================================
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This file is part of FLINT.
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FLINT is free software; you can redistribute it and/or modify
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it under the terms of the GNU General Public License as published by
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the Free Software Foundation; either version 2 of the License, or
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(at your option) any later version.
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FLINT is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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GNU General Public License for more details.
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You should have received a copy of the GNU General Public License
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along with FLINT; if not, write to the Free Software
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Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA
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=============================================================================*/
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/******************************************************************************
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Copyright (C) 2009 William Hart
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Copyright (C) 2011 Sebastian Pancratz
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******************************************************************************/
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#include <gmp.h>
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#include <limits.h>
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#include "flint.h"
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#include "fmpz.h"
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#include "ulong_extras.h"
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void fmpz_powm_ui(fmpz_t f, const fmpz_t g, ulong e, const fmpz_t m)
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{
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if (fmpz_sgn(m) <= 0)
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{
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flint_printf("Exception (fmpz_powm_ui). Modulus is less than 1.\n");
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abort();
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}
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if (fmpz_is_one(m))
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{
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fmpz_zero(f);
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}
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else if (e == 0)
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{
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fmpz_one(f);
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}
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else /* e != 0, m > 0 */
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{
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fmpz g2 = *g;
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fmpz m2 = *m;
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if (!COEFF_IS_MPZ(m2)) /* m is small */
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{
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if (!COEFF_IS_MPZ(g2)) /* g is small */
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{
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mp_limb_t minv = n_preinvert_limb(m2);
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_fmpz_demote(f);
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if (g2 >= 0)
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{
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g2 = n_mod2_preinv(g2, m2, minv);
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*f = n_powmod2_ui_preinv(g2, e, m2, minv);
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}
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else
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{
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g2 = n_mod2_preinv(-g2, m2, minv);
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*f = n_powmod2_ui_preinv(g2, e, m2, minv);
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if ((e & UWORD(1)))
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*f = n_negmod(*f, m2);
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}
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}
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else /* g is large */
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{
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__mpz_struct *ptr = _fmpz_promote(f);
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mpz_t m3;
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flint_mpz_init_set_ui(m3, m2);
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flint_mpz_powm_ui(ptr, COEFF_TO_PTR(g2), e, m3);
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mpz_clear(m3);
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_fmpz_demote_val(f);
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}
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}
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else /* m is large */
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{
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if (!COEFF_IS_MPZ(g2)) /* g is small */
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{
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__mpz_struct *ptr = _fmpz_promote(f);
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mpz_t g3;
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flint_mpz_init_set_si(g3, g2);
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flint_mpz_powm_ui(ptr, g3, e, COEFF_TO_PTR(m2));
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mpz_clear(g3);
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_fmpz_demote_val(f);
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}
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else /* g is large */
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{
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__mpz_struct *ptr = _fmpz_promote(f);
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flint_mpz_powm_ui(ptr, COEFF_TO_PTR(g2), e, COEFF_TO_PTR(m2));
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_fmpz_demote_val(f);
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}
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}
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}
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}
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