Coverage Report

Created: 2024-11-21 07:03

/src/libgmp/mpn/dcpi1_bdiv_q.c
Line
Count
Source (jump to first uncovered line)
1
/* mpn_dcpi1_bdiv_q -- divide-and-conquer Hensel division with precomputed
2
   inverse, returning quotient.
3
4
   Contributed to the GNU project by Niels Möller and Torbjorn Granlund.
5
6
   THE FUNCTIONS IN THIS FILE ARE INTERNAL WITH MUTABLE INTERFACES.  IT IS ONLY
7
   SAFE TO REACH THEM THROUGH DOCUMENTED INTERFACES.  IN FACT, IT IS ALMOST
8
   GUARANTEED THAT THEY WILL CHANGE OR DISAPPEAR IN A FUTURE GMP RELEASE.
9
10
Copyright 2006, 2007, 2009-2011, 2017 Free Software Foundation, Inc.
11
12
This file is part of the GNU MP Library.
13
14
The GNU MP Library is free software; you can redistribute it and/or modify
15
it under the terms of either:
16
17
  * the GNU Lesser General Public License as published by the Free
18
    Software Foundation; either version 3 of the License, or (at your
19
    option) any later version.
20
21
or
22
23
  * the GNU General Public License as published by the Free Software
24
    Foundation; either version 2 of the License, or (at your option) any
25
    later version.
26
27
or both in parallel, as here.
28
29
The GNU MP Library is distributed in the hope that it will be useful, but
30
WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
31
or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
32
for more details.
33
34
You should have received copies of the GNU General Public License and the
35
GNU Lesser General Public License along with the GNU MP Library.  If not,
36
see https://www.gnu.org/licenses/.  */
37
38
#include "gmp-impl.h"
39
40
41
#if 0       /* unused, so leave out for now */
42
static mp_size_t
43
mpn_dcpi1_bdiv_q_n_itch (mp_size_t n)
44
{
45
  /* NOTE: Depends on mullo_n and mpn_dcpi1_bdiv_qr_n interface */
46
  return n;
47
}
48
#endif
49
50
/* Computes Q = - N / D mod B^n, destroys N.
51
52
   N = {np,n}
53
   D = {dp,n}
54
*/
55
56
static void
57
mpn_dcpi1_bdiv_q_n (mp_ptr qp,
58
        mp_ptr np, mp_srcptr dp, mp_size_t n,
59
        mp_limb_t dinv, mp_ptr tp)
60
716
{
61
1.47k
  while (ABOVE_THRESHOLD (n, DC_BDIV_Q_THRESHOLD))
62
758
    {
63
758
      mp_size_t lo, hi;
64
758
      mp_limb_t cy;
65
66
758
      lo = n >> 1;      /* floor(n/2) */
67
758
      hi = n - lo;      /* ceil(n/2) */
68
69
758
      cy = mpn_dcpi1_bdiv_qr_n (qp, np, dp, lo, dinv, tp);
70
71
758
      mpn_mullo_n (tp, qp, dp + hi, lo);
72
758
      mpn_add_n (np + hi, np + hi, tp, lo);
73
74
758
      if (lo < hi)
75
439
  {
76
439
    cy += mpn_addmul_1 (np + lo, qp, lo, dp[lo]);
77
439
    np[n - 1] += cy;
78
439
  }
79
758
      qp += lo;
80
758
      np += lo;
81
758
      n -= lo;
82
758
    }
83
716
  mpn_sbpi1_bdiv_q (qp, np, n, dp, n, dinv);
84
716
}
85
86
/* Computes Q = - N / D mod B^nn, destroys N.
87
88
   N = {np,nn}
89
   D = {dp,dn}
90
*/
91
92
void
93
mpn_dcpi1_bdiv_q (mp_ptr qp,
94
      mp_ptr np, mp_size_t nn,
95
      mp_srcptr dp, mp_size_t dn,
96
      mp_limb_t dinv)
97
716
{
98
716
  mp_size_t qn;
99
716
  mp_limb_t cy;
100
716
  mp_ptr tp;
101
716
  TMP_DECL;
102
103
716
  TMP_MARK;
104
105
716
  ASSERT (dn >= 2);
106
716
  ASSERT (nn - dn >= 0);
107
716
  ASSERT (dp[0] & 1);
108
109
716
  tp = TMP_SALLOC_LIMBS (dn);
110
111
716
  qn = nn;
112
113
716
  if (qn > dn)
114
68
    {
115
      /* Reduce qn mod dn in a super-efficient manner.  */
116
68
      do
117
68
  qn -= dn;
118
68
      while (qn > dn);
119
120
      /* Perform the typically smaller block first.  */
121
68
      if (BELOW_THRESHOLD (qn, DC_BDIV_QR_THRESHOLD))
122
57
  cy = mpn_sbpi1_bdiv_qr (qp, np, 2 * qn, dp, qn, dinv);
123
11
      else
124
11
  cy = mpn_dcpi1_bdiv_qr_n (qp, np, dp, qn, dinv, tp);
125
126
68
      if (qn != dn)
127
68
  {
128
68
    if (qn > dn - qn)
129
11
      mpn_mul (tp, qp, qn, dp + qn, dn - qn);
130
57
    else
131
57
      mpn_mul (tp, dp + qn, dn - qn, qp, qn);
132
68
    mpn_incr_u (tp + qn, cy);
133
134
68
    mpn_add (np + qn, np + qn, nn - qn, tp, dn);
135
68
    cy = 0;
136
68
  }
137
138
68
      np += qn;
139
68
      qp += qn;
140
141
68
      qn = nn - qn;
142
68
      while (qn > dn)
143
0
  {
144
0
    mpn_add_1 (np + dn, np + dn, qn - dn, cy);
145
0
    cy = mpn_dcpi1_bdiv_qr_n (qp, np, dp, dn, dinv, tp);
146
0
    qp += dn;
147
0
    np += dn;
148
0
    qn -= dn;
149
0
  }
150
68
      mpn_dcpi1_bdiv_q_n (qp, np, dp, dn, dinv, tp);
151
68
    }
152
648
  else
153
648
    {
154
648
      if (BELOW_THRESHOLD (qn, DC_BDIV_Q_THRESHOLD))
155
0
  mpn_sbpi1_bdiv_q (qp, np, qn, dp, qn, dinv);
156
648
      else
157
648
  mpn_dcpi1_bdiv_q_n (qp, np, dp, qn, dinv, tp);
158
648
    }
159
160
716
  TMP_FREE;
161
716
}