90 lines
2.1 KiB
C
90 lines
2.1 KiB
C
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/*=============================================================================
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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) 2011 Sebastian Pancratz
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Copyright (C) 2011 Fredrik Johansson
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******************************************************************************/
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#include <math.h>
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#include <gmp.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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slong
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fmpz_clog_ui(const fmpz_t n, ulong b)
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{
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fmpz_t t;
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int sign;
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slong r;
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if (fmpz_is_one(n))
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return 0;
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if (b == 2)
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{
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fmpz_init(t);
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fmpz_sub_ui(t, n, 1);
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r = fmpz_bits(t);
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fmpz_clear(t);
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return r;
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}
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if (!COEFF_IS_MPZ(*n))
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return n_clog(*n, b);
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if (fmpz_cmp_ui(n, b) <= 0)
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return 1;
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r = fmpz_dlog(n) / log(b);
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fmpz_init(t);
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fmpz_set_ui(t, b);
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fmpz_pow_ui(t, t, r);
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sign = fmpz_cmp(t, n);
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/* Adjust down */
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if (sign > 0)
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{
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while (sign > 0)
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{
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fmpz_divexact_ui(t, t, b);
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sign = fmpz_cmp(t, n);
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r--;
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}
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r += (sign != 0);
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}
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/* Adjust up */
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else if (sign < 0)
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{
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while (sign < 0)
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{
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fmpz_mul_ui(t, t, b);
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sign = fmpz_cmp(t, n);
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r++;
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}
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}
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fmpz_clear(t);
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return r;
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}
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