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https://github.com/vale981/arb
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63 lines
1.5 KiB
C
63 lines
1.5 KiB
C
/*
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Copyright (C) 2013 Fredrik Johansson
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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 it under
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the terms of the GNU Lesser General Public License (LGPL) as published
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by the Free Software Foundation; either version 2.1 of the License, or
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(at your option) any later version. See <http://www.gnu.org/licenses/>.
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*/
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#include "fmpr.h"
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slong
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fmpr_set_round_ui_2exp_fmpz(fmpr_t z,
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mp_limb_t lo, const fmpz_t exp, int negative,
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slong prec, fmpr_rnd_t rnd)
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{
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slong lead, trail, bc, shift, shift2, ret;
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shift = 0;
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if ((lo & 1) == 0)
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{
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if (lo == 0)
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{
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fmpr_zero(z);
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return FMPR_RESULT_EXACT;
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}
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count_trailing_zeros(trail, lo);
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lo >>= trail;
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shift = trail;
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}
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count_leading_zeros(lead, lo);
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bc = FLINT_BITS - lead;
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ret = FMPR_RESULT_EXACT;
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if (bc > prec)
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{
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shift2 = bc - prec;
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lo = (lo >> shift2) + rounds_up(rnd, negative);
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count_trailing_zeros(trail, lo);
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lo >>= trail;
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shift += shift2;
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shift += trail;
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ret = trail;
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/* special case: if the mantissa overflowed to the next power of two,
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the error bound must be multiplied by two */
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ret -= (trail == prec);
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}
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if (!negative)
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fmpz_set_ui(fmpr_manref(z), lo);
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else
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fmpz_neg_ui(fmpr_manref(z), lo);
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fmpz_add_si_inline(fmpr_expref(z), exp, shift);
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return ret;
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}
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