1 /* mpf_div -- Divide two floats.
2
3 Copyright 1993, 1994, 1996, 2000, 2001, 2002, 2004, 2005, 2010 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 the GNU Lesser General Public License as published by
10 the Free Software Foundation; either version 3 of the License, or (at your
11 option) any later version.
12
13 The GNU MP Library is distributed in the hope that it will be useful, but
14 WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
15 or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public
16 License for more details.
17
18 You should have received a copy of the GNU Lesser General Public License
19 along with the GNU MP Library. If not, see http://www.gnu.org/licenses/. */
20
21 #include "gmp.h"
22 #include "gmp-impl.h"
23
24
25 /* Not done:
26
27 No attempt is made to identify an overlap u==v. The result will be
28 correct (1.0), but a full actual division is done whereas of course
29 x/x==1 needs no work. Such a call is not a sensible thing to make, and
30 it's left to an application to notice and optimize if it might arise
31 somehow through pointer aliasing or whatever.
32
33 Enhancements:
34
35 The high quotient limb is non-zero when high{up,vsize} >= {vp,vsize}. We
36 could make that comparison and use qsize==prec instead of qsize==prec+1,
37 to save one limb in the division.
38
39 If r==u but the size is enough bigger than prec that there won't be an
40 overlap between quotient and dividend in mpn_tdiv_qr, then we can avoid
41 copying up,usize. This would only arise from a prec reduced with
42 mpf_set_prec_raw and will be pretty unusual, but might be worthwhile if
43 it could be worked into the copy_u decision cleanly. */
44
45 void
mpf_div(mpf_ptr r,mpf_srcptr u,mpf_srcptr v)46 mpf_div (mpf_ptr r, mpf_srcptr u, mpf_srcptr v)
47 {
48 mp_srcptr up, vp;
49 mp_ptr rp, tp, new_vp;
50 mp_size_t usize, vsize, rsize, prospective_rsize, tsize, zeros;
51 mp_size_t sign_quotient, prec, high_zero, chop;
52 mp_exp_t rexp;
53 int copy_u;
54 TMP_DECL;
55
56 usize = SIZ(u);
57 vsize = SIZ(v);
58 sign_quotient = usize ^ vsize;
59 usize = ABS (usize);
60 vsize = ABS (vsize);
61 prec = PREC(r);
62
63 if (vsize == 0)
64 DIVIDE_BY_ZERO;
65
66 if (usize == 0)
67 {
68 SIZ(r) = 0;
69 EXP(r) = 0;
70 return;
71 }
72
73 TMP_MARK;
74 rexp = EXP(u) - EXP(v) + 1;
75
76 rp = PTR(r);
77 up = PTR(u);
78 vp = PTR(v);
79
80 prospective_rsize = usize - vsize + 1; /* quot from using given u,v sizes */
81 rsize = prec + 1; /* desired quot */
82
83 zeros = rsize - prospective_rsize; /* padding u to give rsize */
84 copy_u = (zeros > 0 || rp == up); /* copy u if overlap or padding */
85
86 chop = MAX (-zeros, 0); /* negative zeros means shorten u */
87 up += chop;
88 usize -= chop;
89 zeros += chop; /* now zeros >= 0 */
90
91 tsize = usize + zeros; /* size for possible copy of u */
92
93 /* copy and possibly extend u if necessary */
94 if (copy_u)
95 {
96 tp = TMP_ALLOC_LIMBS (tsize + 1); /* +1 for mpn_div_q's scratch needs */
97 MPN_ZERO (tp, zeros);
98 MPN_COPY (tp+zeros, up, usize);
99 up = tp;
100 usize = tsize;
101 }
102 else
103 {
104 tp = TMP_ALLOC_LIMBS (usize + 1);
105 }
106
107 /* ensure divisor doesn't overlap quotient */
108 if (rp == vp)
109 {
110 new_vp = TMP_ALLOC_LIMBS (vsize);
111 MPN_COPY (new_vp, vp, vsize);
112 vp = new_vp;
113 }
114
115 ASSERT (usize-vsize+1 == rsize);
116 mpn_div_q (rp, up, usize, vp, vsize, tp);
117
118 /* strip possible zero high limb */
119 high_zero = (rp[rsize-1] == 0);
120 rsize -= high_zero;
121 rexp -= high_zero;
122
123 SIZ(r) = sign_quotient >= 0 ? rsize : -rsize;
124 EXP(r) = rexp;
125 TMP_FREE;
126 }
127