1 /* mpfr_random2 -- Generate a positive random mpfr_t of specified size, with
2 long runs of consecutive ones and zeros in the binary representation.
3
4 Copyright 1999, 2001-2004, 2006-2023 Free Software Foundation, Inc.
5 Contributed by the AriC and Caramba projects, INRIA.
6
7 This file is part of the GNU MPFR Library.
8
9 The GNU MPFR Library is free software; you can redistribute it and/or modify
10 it under the terms of the GNU Lesser General Public License as published by
11 the Free Software Foundation; either version 3 of the License, or (at your
12 option) any later version.
13
14 The GNU MPFR Library is distributed in the hope that it will be useful, but
15 WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
16 or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public
17 License for more details.
18
19 You should have received a copy of the GNU Lesser General Public License
20 along with the GNU MPFR Library; see the file COPYING.LESSER. If not, see
21 https://www.gnu.org/licenses/ or write to the Free Software Foundation, Inc.,
22 51 Franklin St, Fifth Floor, Boston, MA 02110-1301, USA. */
23
24 #include "mpfr-test.h"
25
26 #if GMP_NUMB_BITS < 16
27 #define LOGBITS_PER_BLOCK 3
28 #else
29 #define LOGBITS_PER_BLOCK 4
30 #endif
31
32 #if GMP_NUMB_BITS < 32
33 #define BITS_PER_RANDCALL GMP_NUMB_BITS
34 #else
35 #define BITS_PER_RANDCALL 32
36 #endif
37
38 /* exp is the maximum exponent in absolute value */
39 void
mpfr_random2(mpfr_ptr x,mp_size_t size,mpfr_exp_t exp,gmp_randstate_t rstate)40 mpfr_random2 (mpfr_ptr x, mp_size_t size, mpfr_exp_t exp,
41 gmp_randstate_t rstate)
42 {
43 mp_size_t xn, k, ri;
44 unsigned long sh;
45 mp_limb_t *xp;
46 mp_limb_t elimb, ran, acc;
47 int ran_nbits, bit_pos, nb;
48
49 if (MPFR_UNLIKELY(size == 0))
50 {
51 MPFR_SET_ZERO (x);
52 MPFR_SET_POS (x);
53 return ;
54 }
55 else if (size > 0)
56 {
57 MPFR_SET_POS (x);
58 }
59 else
60 {
61 MPFR_SET_NEG (x);
62 size = -size;
63 }
64
65 xn = MPFR_LIMB_SIZE (x);
66 xp = MPFR_MANT (x);
67 if (size > xn)
68 size = xn;
69 k = xn - size;
70
71 /* Code extracted from GMP, function mpn_random2, to avoid the use
72 of GMP's internal random state in MPFR */
73
74 mpfr_rand_raw (&elimb, rstate, BITS_PER_RANDCALL);
75 ran = elimb;
76
77 /* Start off at a random bit position in the most significant limb. */
78 bit_pos = GMP_NUMB_BITS - 1;
79 ran >>= MPFR_LOG2_GMP_NUMB_BITS; /* Ideally log2(GMP_NUMB_BITS) */
80 ran_nbits = BITS_PER_RANDCALL - MPFR_LOG2_GMP_NUMB_BITS; /* Ideally - log2(GMP_NUMB_BITS) */
81
82 /* Bit 0 of ran chooses string of ones/string of zeroes.
83 Make most significant limb be non-zero by setting bit 0 of RAN. */
84 ran |= 1;
85 ri = xn - 1;
86
87 acc = 0;
88 while (ri >= k)
89 {
90 if (ran_nbits < LOGBITS_PER_BLOCK + 1)
91 {
92 mpfr_rand_raw (&elimb, rstate, BITS_PER_RANDCALL);
93 ran = elimb;
94 ran_nbits = BITS_PER_RANDCALL;
95 }
96
97 nb = (ran >> 1) % (1 << LOGBITS_PER_BLOCK) + 1;
98 if ((ran & 1) != 0)
99 {
100 MPFR_ASSERTN (bit_pos < GMP_NUMB_BITS);
101 /* Generate a string of nb ones. */
102 if (nb > bit_pos)
103 {
104 xp[ri--] = acc | MPFR_LIMB_MASK (bit_pos + 1);
105 bit_pos += GMP_NUMB_BITS;
106 bit_pos -= nb;
107 acc = MPFR_LIMB_LSHIFT (MPFR_LIMB_MAX << 1, bit_pos);
108 }
109 else
110 {
111 bit_pos -= nb;
112 acc |= MPFR_LIMB_LSHIFT (MPFR_LIMB_MASK (nb) << 1, bit_pos);
113 }
114 }
115 else
116 {
117 /* Generate a string of nb zeroes. */
118 if (nb > bit_pos)
119 {
120 xp[ri--] = acc;
121 acc = 0;
122 bit_pos += GMP_NUMB_BITS;
123 }
124 bit_pos -= nb;
125 }
126 ran_nbits -= LOGBITS_PER_BLOCK + 1;
127 ran >>= LOGBITS_PER_BLOCK + 1;
128 }
129
130 /* Set mandatory most significant bit. */
131 /* xp[xn - 1] |= MPFR_LIMB_HIGHBIT; */
132
133 if (k != 0)
134 {
135 /* Clear last limbs */
136 MPN_ZERO (xp, k);
137 }
138 else
139 {
140 /* Mask off non significant bits in the low limb. */
141 MPFR_UNSIGNED_MINUS_MODULO (sh, MPFR_PREC (x));
142 xp[0] &= ~MPFR_LIMB_MASK (sh);
143 }
144
145 /* Generate random exponent. */
146 mpfr_rand_raw (&elimb, RANDS, GMP_NUMB_BITS);
147 MPFR_ASSERTN (exp >= 0 && exp <= MPFR_EMAX_MAX);
148 exp = (mpfr_exp_t) (elimb % (2 * exp + 1)) - exp;
149 MPFR_SET_EXP (x, exp);
150
151 return ;
152 }
153