1 /*
2 Copyright (C) 2020 Daniel Schultz
3
4 This file is part of FLINT.
5
6 FLINT is free software: you can redistribute it and/or modify it under
7 the terms of the GNU Lesser General Public License (LGPL) as published
8 by the Free Software Foundation; either version 2.1 of the License, or
9 (at your option) any later version. See <https://www.gnu.org/licenses/>.
10 */
11
12 #include <gmp.h>
13 #include "flint.h"
14 #include "ulong_extras.h"
15 #include "fmpz.h"
16
fmpz_cdiv_r_2exp(fmpz_t f,const fmpz_t g,ulong exp)17 void fmpz_cdiv_r_2exp(fmpz_t f, const fmpz_t g, ulong exp)
18 {
19 fmpz d = *g;
20
21 if (!COEFF_IS_MPZ(d)) /* g is small */
22 {
23 if (d <= 0)
24 {
25 d = -d;
26 fmpz_neg_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_neg_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 mpz_neg(mpz_ptr, mpz_ptr);
42 }
43 }
44 }
45 else /*g is large */
46 {
47 __mpz_struct * mpz_ptr = _fmpz_promote(f); /* g is already large */
48 mpz_cdiv_r_2exp(mpz_ptr, COEFF_TO_PTR(d), exp);
49 _fmpz_demote_val(f); /* division may make value small */
50 }
51 }
52
53