/*
    Copyright (C) 2012, 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"

static slong _fmpr_sub_special(fmpr_t z, const fmpr_t x, const fmpr_t y, slong prec, fmpr_rnd_t rnd)
{
    if (fmpr_is_zero(x))
    {
        return fmpr_neg_round(z, y, prec, rnd);
    }
    else if (fmpr_is_zero(y))
    {
        return fmpr_set_round(z, x, prec, rnd);
    }
    else if (fmpr_is_nan(x) || fmpr_is_nan(y)
        || (fmpr_is_pos_inf(x) && fmpr_is_pos_inf(y))
        || (fmpr_is_neg_inf(x) && fmpr_is_neg_inf(y)))
    {
        fmpr_nan(z);
        return FMPR_RESULT_EXACT;
    }
    else if (fmpr_is_special(x))
    {
        fmpr_set(z, x);
        return FMPR_RESULT_EXACT;
    }
    else
    {
        fmpr_neg(z, y);
        return FMPR_RESULT_EXACT;
    }
}

slong
fmpr_sub(fmpr_t z, const fmpr_t x, const fmpr_t y, slong prec, fmpr_rnd_t rnd)
{
    slong shift, xn, yn;
    mp_limb_t xtmp, ytmp;
    mp_ptr xptr, yptr;
    fmpz xv, yv;
    const fmpz * xexp;
    const fmpz * yexp;
    int xsign, ysign;

    if (fmpr_is_special(x) || fmpr_is_special(y))
    {
        return _fmpr_sub_special(z, x, y, prec, rnd);
    }

    shift = _fmpz_sub_small(fmpr_expref(y), fmpr_expref(x));

    if (shift >= 0)
    {
        xexp = fmpr_expref(x);
        yexp = fmpr_expref(y);
        xv = *fmpr_manref(x);
        yv = *fmpr_manref(y);
    }
    else
    {
        xexp = fmpr_expref(y);
        yexp = fmpr_expref(x);
        xv = *fmpr_manref(y);
        yv = *fmpr_manref(x);
    }

    FMPZ_GET_MPN_READONLY(xsign, xn, xptr, xtmp, xv)
    FMPZ_GET_MPN_READONLY(ysign, yn, yptr, ytmp, yv)

    if (shift >= 0)
    {
        ysign = !ysign;
    }
    else
    {
        shift = -shift;
        xsign = !xsign;
    }

    if ((xn == 1) && (yn == 1) && (shift < FLINT_BITS))
        return _fmpr_add_1x1(z, xptr[0], xsign, xexp, yptr[0], ysign, yexp, shift, prec, rnd);
    else
        return _fmpr_add_mpn(z, xptr, xn, xsign, xexp, yptr, yn, ysign, yexp, shift, prec, rnd);
}


slong
fmpr_sub_ui(fmpr_t z, const fmpr_t x, ulong y, slong prec, fmpr_rnd_t rnd)
{
    fmpr_t t; slong r;
    fmpr_init(t);
    fmpr_set_ui(t, y);
    r = fmpr_sub(z, x, t, prec, rnd);
    fmpr_clear(t);
    return r;
}

slong
fmpr_sub_si(fmpr_t z, const fmpr_t x, slong y, slong prec, fmpr_rnd_t rnd)
{
    fmpr_t t; slong r;
    fmpr_init(t);
    fmpr_set_si(t, y);
    r = fmpr_sub(z, x, t, prec, rnd);
    fmpr_clear(t);
    return r;
}

slong
fmpr_sub_fmpz(fmpr_t z, const fmpr_t x, const fmpz_t y, slong prec, fmpr_rnd_t rnd)
{
    fmpr_t t; slong r;
    fmpr_init(t);
    fmpr_set_fmpz(t, y);
    r = fmpr_sub(z, x, t, prec, rnd);
    fmpr_clear(t);
    return r;
}