mirror of
https://github.com/vale981/arb
synced 2025-03-05 09:21:38 -05:00
88 lines
2.7 KiB
C
88 lines
2.7 KiB
C
/*=============================================================================
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This file is part of ARB.
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ARB 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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ARB 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 ARB; 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) 2013 Fredrik Johansson
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******************************************************************************/
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#include "fmpr.h"
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void
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fmpr_divappr_abs_ubound(fmpr_t z, const fmpr_t x, const fmpr_t y, slong prec)
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{
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if (fmpr_is_special(x) || fmpr_is_special(y) || fmpz_is_pm1(fmpr_manref(y)))
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{
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fmpr_div(z, x, y, prec, FMPR_RND_UP);
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fmpr_abs(z, z);
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}
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else
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{
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fmpz_t t, u;
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slong xbits, ybits, tbits, ubits, shift;
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xbits = fmpz_bits(fmpr_manref(x));
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ybits = fmpz_bits(fmpr_manref(y));
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fmpz_init(t);
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fmpz_init(u);
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ubits = FLINT_MIN(ybits, prec);
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tbits = prec + ubits + 1;
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/* upper bound for |x|, shifted */
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if (xbits <= tbits)
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{
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fmpz_mul_2exp(t, fmpr_manref(x), tbits - xbits);
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fmpz_abs(t, t);
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}
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else if (fmpz_sgn(fmpr_manref(x)) > 0)
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{
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fmpz_cdiv_q_2exp(t, fmpr_manref(x), xbits - tbits);
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}
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else
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{
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fmpz_fdiv_q_2exp(t, fmpr_manref(x), xbits - tbits);
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fmpz_neg(t, t);
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}
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/* lower bound for |y|, shifted */
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if (ybits <= ubits)
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fmpz_mul_2exp(u, fmpr_manref(y), ubits - ybits);
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else
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fmpz_tdiv_q_2exp(u, fmpr_manref(y), ybits - ubits);
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fmpz_abs(u, u);
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fmpz_cdiv_q(fmpr_manref(z), t, u);
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shift = (ubits - ybits) - (tbits - xbits);
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fmpz_sub(fmpr_expref(z), fmpr_expref(x), fmpr_expref(y));
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if (shift >= 0)
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fmpz_add_ui(fmpr_expref(z), fmpr_expref(z), shift);
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else
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fmpz_sub_ui(fmpr_expref(z), fmpr_expref(z), -shift);
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_fmpr_normalise(fmpr_manref(z), fmpr_expref(z), prec, FMPR_RND_UP);
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fmpz_clear(t);
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fmpz_clear(u);
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}
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}
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