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