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/*
Copyright (C) 2013, 2014 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_mul_1x1(fmpr_t z, mp_limb_t u, const fmpz_t xexp, mp_limb_t v,
const fmpz_t yexp, int negative, slong prec, fmpr_rnd_t rnd)
{
slong lead, trail, bc, shift, ret;
mp_limb_t hi, lo;
umul_ppmm(hi, lo, u, v);
shift = 0;
if (hi == 0)
{
/* 1 limb */
count_leading_zeros(lead, lo);
bc = FLINT_BITS - lead;
ret = FMPR_RESULT_EXACT;
if (bc > prec)
{
shift += bc - prec;
lo = (lo >> shift) + rounds_up(rnd, negative);
count_trailing_zeros(trail, lo);
lo >>= trail;
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);
}
else
{
/* 2 limbs */
count_leading_zeros(lead, hi);
bc = 2 * FLINT_BITS - lead;
ret = FMPR_RESULT_EXACT;
if (bc > prec)
{
shift += bc - prec;
/* round */
if (shift < FLINT_BITS)
{
lo = (lo >> shift) | (hi << (FLINT_BITS - shift));
hi >>= shift;
}
else
{
lo = hi >> (shift - FLINT_BITS);
hi = 0;
}
if (rounds_up(rnd, negative))
add_ssaaaa(hi, lo, hi, lo, 0, 1);
/* remove trailing zeros */
if (lo == 0)
{
count_trailing_zeros(trail, hi);
hi >>= trail;
shift += FLINT_BITS + trail;
ret = FLINT_BITS + trail;
/* special case: if the mantissa overflowed to the next power of two,
the error bound must be multiplied by two */
ret -= (FLINT_BITS + trail == prec);
if (!negative)
fmpz_set_ui(fmpr_manref(z), hi);
else
fmpz_neg_ui(fmpr_manref(z), hi);
}
else
{
count_trailing_zeros(trail, lo);
if (trail != 0)
{
lo = (lo >> trail) | (hi << (FLINT_BITS - trail));
hi >>= trail;
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_uiui(fmpr_manref(z), hi, lo);
else
fmpz_neg_uiui(fmpr_manref(z), hi, lo);
}
}
else
{
if (!negative)
fmpz_set_uiui(fmpr_manref(z), hi, lo);
else
fmpz_neg_uiui(fmpr_manref(z), hi, lo);
}
}
fmpz_add2_fmpz_si_inline(fmpr_expref(z), xexp, yexp, shift);
return ret;
}
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