1 /* mpf_div -- Divide two floats.
2
3 Copyright 1993, 1994, 1996, 2000-2002, 2004, 2005, 2010, 2012 Free Software
4 Foundation, Inc.
5
6 This file is part of the GNU MP Library.
7
8 The GNU MP Library is free software; you can redistribute it and/or modify
9 it under the terms of either:
10
11 * the GNU Lesser General Public License as published by the Free
12 Software Foundation; either version 3 of the License, or (at your
13 option) any later version.
14
15 or
16
17 * the GNU General Public License as published by the Free Software
18 Foundation; either version 2 of the License, or (at your option) any
19 later version.
20
21 or both in parallel, as here.
22
23 The GNU MP Library is distributed in the hope that it will be useful, but
24 WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
25 or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
26 for more details.
27
28 You should have received copies of the GNU General Public License and the
29 GNU Lesser General Public License along with the GNU MP Library. If not,
30 see https://www.gnu.org/licenses/. */
31
32 #include "gmp-impl.h"
33
34
35 /* Not done:
36
37 No attempt is made to identify an overlap u==v. The result will be
38 correct (1.0), but a full actual division is done whereas of course
39 x/x==1 needs no work. Such a call is not a sensible thing to make, and
40 it's left to an application to notice and optimize if it might arise
41 somehow through pointer aliasing or whatever.
42
43 Enhancements:
44
45 The high quotient limb is non-zero when high{up,vsize} >= {vp,vsize}. We
46 could make that comparison and use qsize==prec instead of qsize==prec+1,
47 to save one limb in the division.
48
49 If r==u but the size is enough bigger than prec that there won't be an
50 overlap between quotient and dividend in mpn_div_q, then we can avoid
51 copying up,usize. This would only arise from a prec reduced with
52 mpf_set_prec_raw and will be pretty unusual, but might be worthwhile if
53 it could be worked into the copy_u decision cleanly. */
54
55 void
mpf_div(mpf_ptr r,mpf_srcptr u,mpf_srcptr v)56 mpf_div (mpf_ptr r, mpf_srcptr u, mpf_srcptr v)
57 {
58 mp_srcptr up, vp;
59 mp_ptr rp, tp, new_vp;
60 mp_size_t usize, vsize, rsize, prospective_rsize, tsize, zeros;
61 mp_size_t sign_quotient, prec, high_zero, chop;
62 mp_exp_t rexp;
63 int copy_u;
64 TMP_DECL;
65
66 usize = SIZ(u);
67 vsize = SIZ(v);
68
69 if (UNLIKELY (vsize == 0))
70 DIVIDE_BY_ZERO;
71
72 if (usize == 0)
73 {
74 SIZ(r) = 0;
75 EXP(r) = 0;
76 return;
77 }
78
79 sign_quotient = usize ^ vsize;
80 usize = ABS (usize);
81 vsize = ABS (vsize);
82 prec = PREC(r);
83
84 TMP_MARK;
85 rexp = EXP(u) - EXP(v) + 1;
86
87 rp = PTR(r);
88 up = PTR(u);
89 vp = PTR(v);
90
91 prospective_rsize = usize - vsize + 1; /* quot from using given u,v sizes */
92 rsize = prec + 1; /* desired quot */
93
94 zeros = rsize - prospective_rsize; /* padding u to give rsize */
95 copy_u = (zeros > 0 || rp == up); /* copy u if overlap or padding */
96
97 chop = MAX (-zeros, 0); /* negative zeros means shorten u */
98 up += chop;
99 usize -= chop;
100 zeros += chop; /* now zeros >= 0 */
101
102 tsize = usize + zeros; /* size for possible copy of u */
103
104 /* copy and possibly extend u if necessary */
105 if (copy_u)
106 {
107 tp = TMP_ALLOC_LIMBS (tsize + 1); /* +1 for mpn_div_q's scratch needs */
108 MPN_ZERO (tp, zeros);
109 MPN_COPY (tp+zeros, up, usize);
110 up = tp;
111 usize = tsize;
112 }
113 else
114 {
115 tp = TMP_ALLOC_LIMBS (usize + 1);
116 }
117
118 /* ensure divisor doesn't overlap quotient */
119 if (rp == vp)
120 {
121 new_vp = TMP_ALLOC_LIMBS (vsize);
122 MPN_COPY (new_vp, vp, vsize);
123 vp = new_vp;
124 }
125
126 ASSERT (usize-vsize+1 == rsize);
127 mpn_div_q (rp, up, usize, vp, vsize, tp);
128
129 /* strip possible zero high limb */
130 high_zero = (rp[rsize-1] == 0);
131 rsize -= high_zero;
132 rexp -= high_zero;
133
134 SIZ(r) = sign_quotient >= 0 ? rsize : -rsize;
135 EXP(r) = rexp;
136 TMP_FREE;
137 }
138