1 /* mpn_div_qr_1 -- mpn by limb division.
2
3 Contributed to the GNU project by Niels Möller and Torbjörn Granlund
4
5 Copyright 1991, 1993, 1994, 1996, 1998-2000, 2002, 2003, 2013 Free Software
6 Foundation, Inc.
7
8 This file is part of the GNU MP Library.
9
10 The GNU MP Library is free software; you can redistribute it and/or modify
11 it under the terms of either:
12
13 * the GNU Lesser General Public License as published by the Free
14 Software Foundation; either version 3 of the License, or (at your
15 option) any later version.
16
17 or
18
19 * the GNU General Public License as published by the Free Software
20 Foundation; either version 2 of the License, or (at your option) any
21 later version.
22
23 or both in parallel, as here.
24
25 The GNU MP Library is distributed in the hope that it will be useful, but
26 WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
27 or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
28 for more details.
29
30 You should have received copies of the GNU General Public License and the
31 GNU Lesser General Public License along with the GNU MP Library. If not,
32 see https://www.gnu.org/licenses/. */
33
34 #include "gmp-impl.h"
35 #include "longlong.h"
36
37 #ifndef DIV_QR_1_NORM_THRESHOLD
38 #define DIV_QR_1_NORM_THRESHOLD 3
39 #endif
40 #ifndef DIV_QR_1_UNNORM_THRESHOLD
41 #define DIV_QR_1_UNNORM_THRESHOLD 3
42 #endif
43
44 #if GMP_NAIL_BITS > 0
45 #error Nail bits not supported
46 #endif
47
48 /* Divides {up, n} by d. Writes the n-1 low quotient limbs at {qp,
49 * n-1}, and the high quotient limb at *qh. Returns remainder. */
50 mp_limb_t
mpn_div_qr_1(mp_ptr qp,mp_limb_t * qh,mp_srcptr up,mp_size_t n,mp_limb_t d)51 mpn_div_qr_1 (mp_ptr qp, mp_limb_t *qh, mp_srcptr up, mp_size_t n,
52 mp_limb_t d)
53 {
54 unsigned cnt;
55 mp_limb_t uh;
56
57 ASSERT (n > 0);
58 ASSERT (d > 0);
59
60 if (d & GMP_NUMB_HIGHBIT)
61 {
62 /* Normalized case */
63 mp_limb_t dinv, q;
64
65 uh = up[--n];
66
67 q = (uh >= d);
68 *qh = q;
69 uh -= (-q) & d;
70
71 if (BELOW_THRESHOLD (n, DIV_QR_1_NORM_THRESHOLD))
72 {
73 cnt = 0;
74 plain:
75 while (n > 0)
76 {
77 mp_limb_t ul = up[--n];
78 udiv_qrnnd (qp[n], uh, uh, ul, d);
79 }
80 return uh >> cnt;
81 }
82 invert_limb (dinv, d);
83 return mpn_div_qr_1n_pi1 (qp, up, n, uh, d, dinv);
84 }
85 else
86 {
87 /* Unnormalized case */
88 mp_limb_t dinv, ul;
89
90 if (! UDIV_NEEDS_NORMALIZATION
91 && BELOW_THRESHOLD (n, DIV_QR_1_UNNORM_THRESHOLD))
92 {
93 uh = up[--n];
94 udiv_qrnnd (*qh, uh, CNST_LIMB(0), uh, d);
95 cnt = 0;
96 goto plain;
97 }
98
99 count_leading_zeros (cnt, d);
100 d <<= cnt;
101
102 #if HAVE_NATIVE_mpn_div_qr_1u_pi1
103 /* FIXME: Call loop doing on-the-fly normalization */
104 #endif
105
106 /* Shift up front, use qp area for shifted copy. A bit messy,
107 since we have only n-1 limbs available, and shift the high
108 limb manually. */
109 uh = up[--n];
110 ul = (uh << cnt) | mpn_lshift (qp, up, n, cnt);
111 uh >>= (GMP_LIMB_BITS - cnt);
112
113 if (UDIV_NEEDS_NORMALIZATION
114 && BELOW_THRESHOLD (n, DIV_QR_1_UNNORM_THRESHOLD))
115 {
116 udiv_qrnnd (*qh, uh, uh, ul, d);
117 up = qp;
118 goto plain;
119 }
120 invert_limb (dinv, d);
121
122 udiv_qrnnd_preinv (*qh, uh, uh, ul, d, dinv);
123 return mpn_div_qr_1n_pi1 (qp, qp, n, uh, d, dinv) >> cnt;
124 }
125 }
126