1 /*
2 Copyright (C) 2009 William Hart
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 <http://www.gnu.org/licenses/>.
10 */
11
12 #include <stdio.h>
13 #include <stdlib.h>
14 #include <gmp.h>
15 #include "flint.h"
16 #include "ulong_extras.h"
17 #include "fmpz.h"
18
19 void
fmpz_fdiv_qr(fmpz_t f,fmpz_t s,const fmpz_t g,const fmpz_t h)20 fmpz_fdiv_qr(fmpz_t f, fmpz_t s, const fmpz_t g, const fmpz_t h)
21 {
22 fmpz c1 = *g;
23 fmpz c2 = *h;
24
25 if (fmpz_is_zero(h))
26 {
27 flint_printf("Exception (fmpz_fdiv_q). Division by zero.\n");
28 flint_abort();
29 }
30
31 if (!COEFF_IS_MPZ(c1)) /* g is small */
32 {
33 if (!COEFF_IS_MPZ(c2)) /* h is also small */
34 {
35 fmpz q = c1 / c2; /* compute C quotient */
36 fmpz r = c1 - c2 * q; /* compute remainder */
37
38 if ((c2 > WORD(0) && r < WORD(0)) || (c2 < WORD(0) && r > WORD(0)))
39 {
40 q--; /* q cannot overflow as remainder implies |c2| != 1 */
41 r += c2;
42 }
43
44 fmpz_set_si(f, q);
45 fmpz_set_si(s, r);
46 }
47 else /* h is large and g is small */
48 {
49 if (c1 == WORD(0))
50 {
51 fmpz_set_ui(f, WORD(0)); /* g is zero */
52 fmpz_set_si(s, c1);
53 }
54 else if ((c1 < WORD(0) && fmpz_sgn(h) < 0) || (c1 > WORD(0) && fmpz_sgn(h) > 0)) /* signs are the same */
55 {
56 fmpz_zero(f); /* quotient is positive, round down to zero */
57 fmpz_set_si(s, c1);
58 }
59 else
60 {
61 fmpz_add(s, g, h);
62 fmpz_set_si(f, WORD(-1)); /* quotient is negative, round down to minus one */
63 }
64 }
65 }
66 else /* g is large */
67 {
68 __mpz_struct *mpz_ptr, *mpz_ptr2;
69
70 _fmpz_promote(f); /* must not hang on to ptr whilst promoting s */
71 mpz_ptr2 = _fmpz_promote(s);
72 mpz_ptr = COEFF_TO_PTR(*f);
73
74 if (!COEFF_IS_MPZ(c2)) /* h is small */
75 {
76 if (c2 > 0) /* h > 0 */
77 {
78 flint_mpz_fdiv_qr_ui(mpz_ptr, mpz_ptr2, COEFF_TO_PTR(c1), c2);
79 }
80 else
81 {
82 flint_mpz_cdiv_qr_ui(mpz_ptr, mpz_ptr2, COEFF_TO_PTR(c1), -c2);
83 mpz_neg(mpz_ptr, mpz_ptr);
84 }
85 }
86 else /* both are large */
87 {
88 mpz_fdiv_qr(mpz_ptr, mpz_ptr2, COEFF_TO_PTR(c1), COEFF_TO_PTR(c2));
89 }
90 _fmpz_demote_val(f); /* division by h may result in small value */
91 _fmpz_demote_val(s); /* division by h may result in small value */
92 }
93 }
94