1/* mpf_get_ui -- mpf to ulong conversion
2
3Copyright 2001, 2002, 2004 Free Software Foundation, Inc.
4
5This file is part of the GNU MP Library.
6
7The GNU MP Library is free software; you can redistribute it and/or modify
8it under the terms of either:
9
10  * the GNU Lesser General Public License as published by the Free
11    Software Foundation; either version 3 of the License, or (at your
12    option) any later version.
13
14or
15
16  * the GNU General Public License as published by the Free Software
17    Foundation; either version 2 of the License, or (at your option) any
18    later version.
19
20or both in parallel, as here.
21
22The GNU MP Library is distributed in the hope that it will be useful, but
23WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
24or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
25for more details.
26
27You should have received copies of the GNU General Public License and the
28GNU Lesser General Public License along with the GNU MP Library.  If not,
29see https://www.gnu.org/licenses/.  */
30
31#include "gmp-impl.h"
32
33
34/* Any fraction bits are truncated, meaning simply discarded.
35
36   For values bigger than a ulong, the low bits are returned (the low
37   absolute value bits actually), like mpz_get_ui, but this isn't
38   documented.
39
40   Notice this is equivalent to mpz_set_f + mpz_get_ui.
41
42
43   Implementation:
44
45   The limb just above the radix point for us to extract is ptr[size-exp].
46
47   We need to check that the size-exp index falls in our available data
48   range, 0 to size-1 inclusive.  We test this without risk of an overflow
49   involving exp by requiring size>=exp (giving size-exp >= 0) and exp>0
50   (giving size-exp <= size-1).
51
52   Notice if size==0 there's no fetch, since of course size>=exp and exp>0
53   can only be true if size>0.  So there's no special handling for size==0,
54   it comes out as 0 the same as any other time we have no data at our
55   target index.
56
57   For nails, the second limb above the radix point is also required, this
58   is ptr[size-exp+1].
59
60   Again we need to check that size-exp+1 falls in our data range, 0 to
61   size-1 inclusive.  We test without risk of overflow by requiring
62   size+1>=exp (giving size-exp+1 >= 0) and exp>1 (giving size-exp+1 <=
63   size-1).
64
65   And again if size==0 these second fetch conditions are not satisfied
66   either since size+1>=exp and exp>1 are only true if size>0.
67
68   The code is arranged with exp>0 wrapping the exp>1 test since exp>1 is
69   mis-compiled by alpha gcc prior to version 3.4.  It re-writes it as
70   exp-1>0, which is incorrect when exp==MP_EXP_T_MIN.  By having exp>0
71   tested first we ensure MP_EXP_T_MIN doesn't reach exp>1.  */
72
73unsigned long
74mpf_get_ui (mpf_srcptr f) __GMP_NOTHROW
75{
76  mp_size_t size;
77  mp_exp_t exp;
78  mp_srcptr fp;
79  mp_limb_t fl;
80
81  exp = EXP (f);
82  size = SIZ (f);
83  fp = PTR (f);
84
85  fl = 0;
86  if (exp > 0)
87    {
88      /* there are some limbs above the radix point */
89
90      size = ABS (size);
91      if (size >= exp)
92        fl = fp[size-exp];
93
94#if BITS_PER_ULONG > GMP_NUMB_BITS
95      if (exp > 1 && size+1 >= exp)
96        fl += (fp[size-exp+1] << GMP_NUMB_BITS);
97#endif
98    }
99
100  return (unsigned long) fl;
101}
102