1 /*
2 Copyright (C) 2009 William Hart
3 Copyright (C) 2011 Sebastian Pancratz
4
5 This file is part of FLINT.
6
7 FLINT is free software: you can redistribute it and/or modify it under
8 the terms of the GNU Lesser General Public License (LGPL) as published
9 by the Free Software Foundation; either version 2.1 of the License, or
10 (at your option) any later version. See <http://www.gnu.org/licenses/>.
11 */
12
13 #include <gmp.h>
14 #include "flint.h"
15 #include "ulong_extras.h"
16 #include "fmpz.h"
17
fmpz_fdiv_r_2exp(fmpz_t f,const fmpz_t g,ulong exp)18 void fmpz_fdiv_r_2exp(fmpz_t f, const fmpz_t g, ulong exp)
19 {
20 fmpz d = *g;
21
22 if (!COEFF_IS_MPZ(d)) /* g is small */
23 {
24 if (d >= 0)
25 {
26 fmpz_set_ui(f, exp < (FLINT_BITS - 2) ? d & ((WORD(1) << exp) - 1) : d);
27 }
28 else
29 {
30 if (exp <= FLINT_BITS - 2)
31 {
32 fmpz_set_ui(f, d & ((WORD(1) << exp) - 1));
33 }
34 else
35 {
36 __mpz_struct * mpz_ptr = _fmpz_promote(f);
37
38 flint_mpz_set_ui(mpz_ptr, 1);
39 mpz_mul_2exp(mpz_ptr, mpz_ptr, exp);
40 flint_mpz_sub_ui(mpz_ptr, mpz_ptr, -d);
41 }
42 }
43 }
44 else /*g is large */
45 {
46 __mpz_struct * mpz_ptr = _fmpz_promote(f); /* g is already large */
47 mpz_fdiv_r_2exp(mpz_ptr, COEFF_TO_PTR(d), exp);
48 _fmpz_demote_val(f); /* division may make value small */
49 }
50 }
51
52