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/*
Copyright (C) 2009 William Hart
This file is part of FLINT.
FLINT 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 3 of the License, or
(at your option) any later version. See <https://www.gnu.org/licenses/>.
*/
#include "gmpcompat.h"
#include "fmpz.h"
void
fmpz_sub(fmpz_t f, const fmpz_t g, const fmpz_t h)
{
fmpz c1 = *g;
fmpz c2 = *h;
if (!COEFF_IS_MPZ(c1)) /* g is small */
{
if (!COEFF_IS_MPZ(c2)) /* both inputs are small */
{
fmpz_set_si(f, c1 - c2);
}
else /* g is small, h is large */
{
mpz_ptr mpz3 = _fmpz_promote(f); /* g is saved and h is large */
mpz_ptr mpz2 = COEFF_TO_PTR(c2);
if (c1 < WORD(0))
{
flint_mpz_add_ui(mpz3, mpz2, -c1);
mpz_neg(mpz3, mpz3);
}
else
flint_mpz_ui_sub(mpz3, c1, mpz2);
_fmpz_demote_val(f); /* may have cancelled */
}
}
else
{
if (!COEFF_IS_MPZ(c2)) /* g is large, h is small */
{
mpz_ptr mpz3 = _fmpz_promote(f); /* h is saved and g is large */
mpz_ptr mpz1 = COEFF_TO_PTR(c1);
if (c2 < WORD(0))
flint_mpz_add_ui(mpz3, mpz1, -c2);
else
flint_mpz_sub_ui(mpz3, mpz1, c2);
_fmpz_demote_val(f); /* may have cancelled */
}
else /* g and h are large */
{
mpz_ptr mpz3 = _fmpz_promote(f); /* aliasing means f is already large */
mpz_ptr mpz1 = COEFF_TO_PTR(c1);
mpz_ptr mpz2 = COEFF_TO_PTR(c2);
mpz_sub(mpz3, mpz1, mpz2);
_fmpz_demote_val(f); /* may have cancelled */
}
}
}