libstdc++: opt_random.h Source File

libstdc++

opt_random.h
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1// Optimizations for random number functions, x86 version -*- C++ -*-
2
3// Copyright (C) 2012-2026 Free Software Foundation, Inc.
4//
5// This file is part of the GNU ISO C++ Library. This library is free
6// software; you can redistribute it and/or modify it under the
7// terms of the GNU General Public License as published by the
8// Free Software Foundation; either version 3, or (at your option)
9// any later version.
10
11// This library is distributed in the hope that it will be useful,
12// but WITHOUT ANY WARRANTY; without even the implied warranty of
13// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
14// GNU General Public License for more details.
15
16// Under Section 7 of GPL version 3, you are granted additional
17// permissions described in the GCC Runtime Library Exception, version
18// 3.1, as published by the Free Software Foundation.
19
20// You should have received a copy of the GNU General Public License and
21// a copy of the GCC Runtime Library Exception along with this program;
22// see the files COPYING3 and COPYING.RUNTIME respectively. If not, see
23// <http://www.gnu.org/licenses/>.
24
25/** @file bits/opt_random.h
26 * This is an internal header file, included by other library headers.
27 * Do not attempt to use it directly. @headername{random}
28 */
29
30#ifndef _BITS_OPT_RANDOM_H
31#define _BITS_OPT_RANDOM_H 1
32
33#ifdef __SSE3__
34#include <pmmintrin.h>
35#endif
36
37
38#pragma GCC system_header
39
40
41namespace std _GLIBCXX_VISIBILITY(default)
42{
43_GLIBCXX_BEGIN_NAMESPACE_VERSION
44
45#ifdef __SSE3__
46 template<>
47 template<typename _UniformRandomNumberGenerator>
48 void
49 normal_distribution<double>::
50 __generate(typename normal_distribution<double>::result_type* __f,
51 typename normal_distribution<double>::result_type* __t,
52 _UniformRandomNumberGenerator& __urng,
53 const param_type& __param)
54 {
55 typedef uint64_t __uctype;
56
57 if (__f == __t)
58 return;
59
60 if (_M_saved_available)
61 {
62 _M_saved_available = false;
63 *__f++ = _M_saved * __param.stddev() + __param.mean();
64
65 if (__f == __t)
66 return;
67 }
68
69 constexpr uint64_t __maskval = 0xfffffffffffffull;
70 static const __m128i __mask = _mm_set1_epi64x(__maskval);
71 static const __m128i __two = _mm_set1_epi64x(0x4000000000000000ull);
72 static const __m128d __three = _mm_set1_pd(3.0);
73 const __m128d __av = _mm_set1_pd(__param.mean());
74
75 const __uctype __urngmin = __urng.min();
76 const __uctype __urngmax = __urng.max();
77 const __uctype __urngrange = __urngmax - __urngmin;
78 const __uctype __uerngrange = __urngrange + 1;
79
80 while (__f + 1 < __t)
81 {
82 double __le;
83 __m128d __x;
84 do
85 {
86 union
87 {
88 __m128i __i;
89 __m128d __d;
90 } __v;
91
92 if (__urngrange > __maskval)
93 {
94 if (__detail::_Power_of_2(__uerngrange))
95 __v.__i = _mm_and_si128(_mm_set_epi64x(__urng(),
96 __urng()),
97 __mask);
98 else
99 {
100 const __uctype __uerange = __maskval + 1;
101 const __uctype __scaling = __urngrange / __uerange;
102 const __uctype __past = __uerange * __scaling;
103 uint64_t __v1;
104 do
105 __v1 = __uctype(__urng()) - __urngmin;
106 while (__v1 >= __past);
107 __v1 /= __scaling;
108 uint64_t __v2;
109 do
110 __v2 = __uctype(__urng()) - __urngmin;
111 while (__v2 >= __past);
112 __v2 /= __scaling;
113
114 __v.__i = _mm_set_epi64x(__v1, __v2);
115 }
116 }
117 else if (__urngrange == __maskval)
118 __v.__i = _mm_set_epi64x(__urng(), __urng());
119 else if ((__urngrange + 2) * __urngrange >= __maskval
120 && __detail::_Power_of_2(__uerngrange))
121 {
122 uint64_t __v1 = __urng() * __uerngrange + __urng();
123 uint64_t __v2 = __urng() * __uerngrange + __urng();
124
125 __v.__i = _mm_and_si128(_mm_set_epi64x(__v1, __v2),
126 __mask);
127 }
128 else
129 {
130 size_t __nrng = 2;
131 __uctype __high = __maskval / __uerngrange / __uerngrange;
132 while (__high > __uerngrange)
133 {
134 ++__nrng;
135 __high /= __uerngrange;
136 }
137 const __uctype __highrange = __high + 1;
138 const __uctype __scaling = __urngrange / __highrange;
139 const __uctype __past = __highrange * __scaling;
140 __uctype __tmp;
141
142 uint64_t __v1;
143 do
144 {
145 do
146 __tmp = __uctype(__urng()) - __urngmin;
147 while (__tmp >= __past);
148 __v1 = __tmp / __scaling;
149 for (size_t __cnt = 0; __cnt < __nrng; ++__cnt)
150 {
151 __tmp = __v1;
152 __v1 *= __uerngrange;
153 __v1 += __uctype(__urng()) - __urngmin;
154 }
155 }
156 while (__v1 > __maskval || __v1 < __tmp);
157
158 uint64_t __v2;
159 do
160 {
161 do
162 __tmp = __uctype(__urng()) - __urngmin;
163 while (__tmp >= __past);
164 __v2 = __tmp / __scaling;
165 for (size_t __cnt = 0; __cnt < __nrng; ++__cnt)
166 {
167 __tmp = __v2;
168 __v2 *= __uerngrange;
169 __v2 += __uctype(__urng()) - __urngmin;
170 }
171 }
172 while (__v2 > __maskval || __v2 < __tmp);
173
174 __v.__i = _mm_set_epi64x(__v1, __v2);
175 }
176
177 __v.__i = _mm_or_si128(__v.__i, __two);
178 __x = _mm_sub_pd(__v.__d, __three);
179 __m128d __m = _mm_mul_pd(__x, __x);
180 __le = _mm_cvtsd_f64(_mm_hadd_pd (__m, __m));
181 }
182 while (__le == 0.0 || __le >= 1.0);
183
184 double __mult = (std::sqrt(-2.0 * std::log(__le) / __le)
185 * __param.stddev());
186
187 __x = _mm_add_pd(_mm_mul_pd(__x, _mm_set1_pd(__mult)), __av);
188
189 _mm_storeu_pd(__f, __x);
190 __f += 2;
191 }
192
193 if (__f != __t)
194 {
195 result_type __x, __y, __r2;
196
197 __detail::_Adaptor<_UniformRandomNumberGenerator, result_type>
198 __aurng(__urng);
199
200 do
201 {
202 __x = result_type(2.0) * __aurng() - 1.0;
203 __y = result_type(2.0) * __aurng() - 1.0;
204 __r2 = __x * __x + __y * __y;
205 }
206 while (__r2 > 1.0 || __r2 == 0.0);
207
208 const result_type __mult = std::sqrt(-2 * std::log(__r2) / __r2);
209 _M_saved = __x * __mult;
210 _M_saved_available = true;
211 *__f = __y * __mult * __param.stddev() + __param.mean();
212 }
213 }
214#endif
215
216
217_GLIBCXX_END_NAMESPACE_VERSION
218} // namespace
219
220
221#endif // _BITS_OPT_RANDOM_H
std::log
complex< _Tp > log(const complex< _Tp > &)
Return complex natural logarithm of z.
Definition complex:1162
std::sqrt
complex< _Tp > sqrt(const complex< _Tp > &)
Return complex square root of z.
Definition complex:1271
std
ISO C++ entities toplevel namespace is std.
std::normal_distribution
A normal continuous distribution for random numbers.
Definition random.h:2730
std::normal_distribution::result_type
_RealType result_type
Definition random.h:2736