1 /* mpfr_eq -- Compare two floats up to a specified bit #.
2
3 Copyright 1999, 2001, 2003-2004, 2006-2023 Free Software Foundation, Inc.
4 Contributed by the AriC and Caramba projects, INRIA.
5
6 This file is part of the GNU MPFR Library.
7
8 The GNU MPFR 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 MPFR 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 MPFR Library; see the file COPYING.LESSER. If not, see
20 https://www.gnu.org/licenses/ or write to the Free Software Foundation, Inc.,
21 51 Franklin St, Fifth Floor, Boston, MA 02110-1301, USA. */
22
23
24 #include "mpfr-impl.h"
25
26 /* return non-zero if the first n_bits bits of u, v are equal,
27 0 otherwise */
28 int
29 mpfr_eq (mpfr_srcptr u, mpfr_srcptr v, unsigned long int n_bits)
30 {
31 mpfr_limb_srcptr up, vp;
32 mp_size_t usize, vsize, size, i;
33 mpfr_exp_t uexp, vexp;
34 int k;
35
36 if (MPFR_ARE_SINGULAR(u, v))
37 {
38 if (MPFR_IS_NAN(u) || MPFR_IS_NAN(v))
39 return 0; /* non equal */
40 else if (MPFR_IS_INF(u) && MPFR_IS_INF(v))
41 return (MPFR_SIGN(u) == MPFR_SIGN(v));
42 else if (MPFR_IS_ZERO(u) && MPFR_IS_ZERO(v))
43 return 1;
44 else
45 return 0;
46 }
47
48 /* 1. Are the signs different? */
49 if (MPFR_SIGN(u) != MPFR_SIGN(v))
50 return 0;
51
52 uexp = MPFR_GET_EXP (u);
53 vexp = MPFR_GET_EXP (v);
54
55 /* 2. Are the exponents different? */
56 if (uexp != vexp)
57 return 0; /* no bit agree */
58
59 usize = MPFR_LIMB_SIZE (u);
60 vsize = MPFR_LIMB_SIZE (v);
61
62 if (vsize > usize) /* exchange u and v */
63 {
64 up = MPFR_MANT(v);
65 vp = MPFR_MANT(u);
66 size = vsize;
67 vsize = usize;
68 usize = size;
69 }
70 else
71 {
72 up = MPFR_MANT(u);
73 vp = MPFR_MANT(v);
74 }
75
76 /* now usize >= vsize */
77 MPFR_ASSERTD(usize >= vsize);
78
79 if (usize > vsize)
80 {
81 if ((unsigned long) vsize * GMP_NUMB_BITS < n_bits)
82 {
83 /* check if low min(PREC(u), n_bits) - (vsize * GMP_NUMB_BITS)
84 bits from u are non-zero */
85 unsigned long remains = n_bits - (vsize * GMP_NUMB_BITS);
86 k = usize - vsize - 1;
87 while (k >= 0 && remains >= GMP_NUMB_BITS && !up[k])
88 {
89 k--;
90 remains -= GMP_NUMB_BITS;
91 }
92 /* now either k < 0: all low bits from u are zero
93 or remains < GMP_NUMB_BITS: check high bits from up[k]
94 or up[k] <> 0: different */
95 if (k >= 0 && (((remains < GMP_NUMB_BITS) &&
96 (up[k] >> (GMP_NUMB_BITS - remains))) ||
97 (remains >= GMP_NUMB_BITS && up[k])))
98 return 0; /* surely too different */
99 }
100 size = vsize;
101 }
102 else
103 {
104 size = usize;
105 }
106
107 /* now size = min (usize, vsize) */
108
109 /* If size is too large wrt n_bits, reduce it to look only at the
110 high n_bits bits.
111 Otherwise, if n_bits > size * GMP_NUMB_BITS, reduce n_bits to
112 size * GMP_NUMB_BITS, since the extra low bits of one of the
113 operands have already been check above. */
114 if ((unsigned long) size > 1 + (n_bits - 1) / GMP_NUMB_BITS)
115 size = 1 + (n_bits - 1) / GMP_NUMB_BITS;
116 else if (n_bits > (unsigned long) size * GMP_NUMB_BITS)
117 n_bits = size * GMP_NUMB_BITS;
118
119 up += usize - size;
120 vp += vsize - size;
121
122 for (i = size - 1; i > 0 && n_bits >= GMP_NUMB_BITS; i--)
123 {
124 if (up[i] != vp[i])
125 return 0;
126 n_bits -= GMP_NUMB_BITS;
127 }
128
129 /* now either i=0 or n_bits<GMP_NUMB_BITS */
130
131 /* since n_bits <= size * GMP_NUMB_BITS before the above for-loop,
132 we have the invariant n_bits <= (i+1) * GMP_NUMB_BITS, thus
133 we always have n_bits <= GMP_NUMB_BITS here */
134 MPFR_ASSERTD(n_bits <= GMP_NUMB_BITS);
135
136 if (n_bits & (GMP_NUMB_BITS - 1))
137 return (up[i] >> (GMP_NUMB_BITS - (n_bits & (GMP_NUMB_BITS - 1))) ==
138 vp[i] >> (GMP_NUMB_BITS - (n_bits & (GMP_NUMB_BITS - 1))));
139 else
140 return (up[i] == vp[i]);
141 }