1 // Copyright 2017 The Abseil Authors.
2 //
3 // Licensed under the Apache License, Version 2.0 (the "License");
4 // you may not use this file except in compliance with the License.
5 // You may obtain a copy of the License at
6 //
7 // https://www.apache.org/licenses/LICENSE-2.0
8 //
9 // Unless required by applicable law or agreed to in writing, software
10 // distributed under the License is distributed on an "AS IS" BASIS,
11 // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
12 // See the License for the specific language governing permissions and
13 // limitations under the License.
14
15 #include "absl/random/internal/fast_uniform_bits.h"
16
17 #include <random>
18
19 #include "gtest/gtest.h"
20
21 namespace absl {
22 ABSL_NAMESPACE_BEGIN
23 namespace random_internal {
24 namespace {
25
26 template <typename IntType>
27 class FastUniformBitsTypedTest : public ::testing::Test {};
28
29 using IntTypes = ::testing::Types<uint8_t, uint16_t, uint32_t, uint64_t>;
30
31 TYPED_TEST_SUITE(FastUniformBitsTypedTest, IntTypes);
32
TYPED_TEST(FastUniformBitsTypedTest,BasicTest)33 TYPED_TEST(FastUniformBitsTypedTest, BasicTest) {
34 using Limits = std::numeric_limits<TypeParam>;
35 using FastBits = FastUniformBits<TypeParam>;
36
37 EXPECT_EQ(0, (FastBits::min)());
38 EXPECT_EQ((Limits::max)(), (FastBits::max)());
39
40 constexpr int kIters = 10000;
41 std::random_device rd;
42 std::mt19937 gen(rd());
43 FastBits fast;
44 for (int i = 0; i < kIters; i++) {
45 const auto v = fast(gen);
46 EXPECT_LE(v, (FastBits::max)());
47 EXPECT_GE(v, (FastBits::min)());
48 }
49 }
50
51 template <typename UIntType, UIntType Lo, UIntType Hi, UIntType Val = Lo>
52 struct FakeUrbg {
53 using result_type = UIntType;
54
55 FakeUrbg() = default;
FakeUrbgabsl::random_internal::__anon145949b50111::FakeUrbg56 explicit FakeUrbg(bool r) : reject(r) {}
57
result_typeabsl::random_internal::__anon145949b50111::FakeUrbg58 static constexpr result_type(max)() { return Hi; }
result_typeabsl::random_internal::__anon145949b50111::FakeUrbg59 static constexpr result_type(min)() { return Lo; }
operator ()absl::random_internal::__anon145949b50111::FakeUrbg60 result_type operator()() {
61 // when reject is set, return Hi half the time.
62 return ((++calls % 2) == 1 && reject) ? Hi : Val;
63 }
64
65 bool reject = false;
66 size_t calls = 0;
67 };
68
TEST(FastUniformBitsTest,IsPowerOfTwoOrZero)69 TEST(FastUniformBitsTest, IsPowerOfTwoOrZero) {
70 EXPECT_TRUE(IsPowerOfTwoOrZero(uint8_t{0}));
71 EXPECT_TRUE(IsPowerOfTwoOrZero(uint8_t{1}));
72 EXPECT_TRUE(IsPowerOfTwoOrZero(uint8_t{2}));
73 EXPECT_FALSE(IsPowerOfTwoOrZero(uint8_t{3}));
74 EXPECT_TRUE(IsPowerOfTwoOrZero(uint8_t{4}));
75 EXPECT_TRUE(IsPowerOfTwoOrZero(uint8_t{16}));
76 EXPECT_FALSE(IsPowerOfTwoOrZero(uint8_t{17}));
77 EXPECT_FALSE(IsPowerOfTwoOrZero((std::numeric_limits<uint8_t>::max)()));
78
79 EXPECT_TRUE(IsPowerOfTwoOrZero(uint16_t{0}));
80 EXPECT_TRUE(IsPowerOfTwoOrZero(uint16_t{1}));
81 EXPECT_TRUE(IsPowerOfTwoOrZero(uint16_t{2}));
82 EXPECT_FALSE(IsPowerOfTwoOrZero(uint16_t{3}));
83 EXPECT_TRUE(IsPowerOfTwoOrZero(uint16_t{4}));
84 EXPECT_TRUE(IsPowerOfTwoOrZero(uint16_t{16}));
85 EXPECT_FALSE(IsPowerOfTwoOrZero(uint16_t{17}));
86 EXPECT_FALSE(IsPowerOfTwoOrZero((std::numeric_limits<uint16_t>::max)()));
87
88 EXPECT_TRUE(IsPowerOfTwoOrZero(uint32_t{0}));
89 EXPECT_TRUE(IsPowerOfTwoOrZero(uint32_t{1}));
90 EXPECT_TRUE(IsPowerOfTwoOrZero(uint32_t{2}));
91 EXPECT_FALSE(IsPowerOfTwoOrZero(uint32_t{3}));
92 EXPECT_TRUE(IsPowerOfTwoOrZero(uint32_t{32}));
93 EXPECT_FALSE(IsPowerOfTwoOrZero(uint32_t{17}));
94 EXPECT_FALSE(IsPowerOfTwoOrZero((std::numeric_limits<uint32_t>::max)()));
95
96 EXPECT_TRUE(IsPowerOfTwoOrZero(uint64_t{0}));
97 EXPECT_TRUE(IsPowerOfTwoOrZero(uint64_t{1}));
98 EXPECT_TRUE(IsPowerOfTwoOrZero(uint64_t{2}));
99 EXPECT_FALSE(IsPowerOfTwoOrZero(uint64_t{3}));
100 EXPECT_TRUE(IsPowerOfTwoOrZero(uint64_t{4}));
101 EXPECT_TRUE(IsPowerOfTwoOrZero(uint64_t{64}));
102 EXPECT_FALSE(IsPowerOfTwoOrZero(uint64_t{17}));
103 EXPECT_FALSE(IsPowerOfTwoOrZero((std::numeric_limits<uint64_t>::max)()));
104 }
105
TEST(FastUniformBitsTest,IntegerLog2)106 TEST(FastUniformBitsTest, IntegerLog2) {
107 EXPECT_EQ(0, IntegerLog2(uint16_t{0}));
108 EXPECT_EQ(0, IntegerLog2(uint16_t{1}));
109 EXPECT_EQ(1, IntegerLog2(uint16_t{2}));
110 EXPECT_EQ(1, IntegerLog2(uint16_t{3}));
111 EXPECT_EQ(2, IntegerLog2(uint16_t{4}));
112 EXPECT_EQ(2, IntegerLog2(uint16_t{5}));
113 EXPECT_EQ(2, IntegerLog2(uint16_t{7}));
114 EXPECT_EQ(3, IntegerLog2(uint16_t{8}));
115 EXPECT_EQ(63, IntegerLog2((std::numeric_limits<uint64_t>::max)()));
116 }
117
TEST(FastUniformBitsTest,RangeSize)118 TEST(FastUniformBitsTest, RangeSize) {
119 EXPECT_EQ(2, (RangeSize<FakeUrbg<uint8_t, 0, 1>>()));
120 EXPECT_EQ(3, (RangeSize<FakeUrbg<uint8_t, 0, 2>>()));
121 EXPECT_EQ(4, (RangeSize<FakeUrbg<uint8_t, 0, 3>>()));
122 // EXPECT_EQ(0, (RangeSize<FakeUrbg<uint8_t, 2, 2>>()));
123 EXPECT_EQ(4, (RangeSize<FakeUrbg<uint8_t, 2, 5>>()));
124 EXPECT_EQ(5, (RangeSize<FakeUrbg<uint8_t, 2, 6>>()));
125 EXPECT_EQ(9, (RangeSize<FakeUrbg<uint8_t, 2, 10>>()));
126 EXPECT_EQ(
127 0, (RangeSize<
128 FakeUrbg<uint8_t, 0, (std::numeric_limits<uint8_t>::max)()>>()));
129
130 EXPECT_EQ(4, (RangeSize<FakeUrbg<uint16_t, 0, 3>>()));
131 EXPECT_EQ(4, (RangeSize<FakeUrbg<uint16_t, 2, 5>>()));
132 EXPECT_EQ(5, (RangeSize<FakeUrbg<uint16_t, 2, 6>>()));
133 EXPECT_EQ(18, (RangeSize<FakeUrbg<uint16_t, 1000, 1017>>()));
134 EXPECT_EQ(
135 0, (RangeSize<
136 FakeUrbg<uint16_t, 0, (std::numeric_limits<uint16_t>::max)()>>()));
137
138 EXPECT_EQ(4, (RangeSize<FakeUrbg<uint32_t, 0, 3>>()));
139 EXPECT_EQ(4, (RangeSize<FakeUrbg<uint32_t, 2, 5>>()));
140 EXPECT_EQ(5, (RangeSize<FakeUrbg<uint32_t, 2, 6>>()));
141 EXPECT_EQ(18, (RangeSize<FakeUrbg<uint32_t, 1000, 1017>>()));
142 EXPECT_EQ(0, (RangeSize<FakeUrbg<uint32_t, 0, 0xffffffff>>()));
143 EXPECT_EQ(0xffffffff, (RangeSize<FakeUrbg<uint32_t, 1, 0xffffffff>>()));
144 EXPECT_EQ(0xfffffffe, (RangeSize<FakeUrbg<uint32_t, 1, 0xfffffffe>>()));
145 EXPECT_EQ(0xfffffffd, (RangeSize<FakeUrbg<uint32_t, 2, 0xfffffffe>>()));
146 EXPECT_EQ(
147 0, (RangeSize<
148 FakeUrbg<uint32_t, 0, (std::numeric_limits<uint32_t>::max)()>>()));
149
150 EXPECT_EQ(4, (RangeSize<FakeUrbg<uint64_t, 0, 3>>()));
151 EXPECT_EQ(4, (RangeSize<FakeUrbg<uint64_t, 2, 5>>()));
152 EXPECT_EQ(5, (RangeSize<FakeUrbg<uint64_t, 2, 6>>()));
153 EXPECT_EQ(18, (RangeSize<FakeUrbg<uint64_t, 1000, 1017>>()));
154 EXPECT_EQ(0x100000000, (RangeSize<FakeUrbg<uint64_t, 0, 0xffffffff>>()));
155 EXPECT_EQ(0xffffffff, (RangeSize<FakeUrbg<uint64_t, 1, 0xffffffff>>()));
156 EXPECT_EQ(0xfffffffe, (RangeSize<FakeUrbg<uint64_t, 1, 0xfffffffe>>()));
157 EXPECT_EQ(0xfffffffd, (RangeSize<FakeUrbg<uint64_t, 2, 0xfffffffe>>()));
158 EXPECT_EQ(0, (RangeSize<FakeUrbg<uint64_t, 0, 0xffffffffffffffff>>()));
159 EXPECT_EQ(0xffffffffffffffff,
160 (RangeSize<FakeUrbg<uint64_t, 1, 0xffffffffffffffff>>()));
161 EXPECT_EQ(0xfffffffffffffffe,
162 (RangeSize<FakeUrbg<uint64_t, 1, 0xfffffffffffffffe>>()));
163 EXPECT_EQ(0xfffffffffffffffd,
164 (RangeSize<FakeUrbg<uint64_t, 2, 0xfffffffffffffffe>>()));
165 EXPECT_EQ(
166 0, (RangeSize<
167 FakeUrbg<uint64_t, 0, (std::numeric_limits<uint64_t>::max)()>>()));
168 }
169
170 // The constants need to be choosen so that an infinite rejection loop doesn't
171 // happen...
172 using Urng1_5bit = FakeUrbg<uint8_t, 0, 2, 0>; // ~1.5 bits (range 3)
173 using Urng4bits = FakeUrbg<uint8_t, 1, 0x10, 2>;
174 using Urng22bits = FakeUrbg<uint32_t, 0, 0x3fffff, 0x301020>;
175 using Urng31bits = FakeUrbg<uint32_t, 1, 0xfffffffe, 0x60070f03>; // ~31.9 bits
176 using Urng32bits = FakeUrbg<uint32_t, 0, 0xffffffff, 0x74010f01>;
177 using Urng33bits =
178 FakeUrbg<uint64_t, 1, 0x1ffffffff, 0x013301033>; // ~32.9 bits
179 using Urng63bits = FakeUrbg<uint64_t, 1, 0xfffffffffffffffe,
180 0xfedcba9012345678>; // ~63.9 bits
181 using Urng64bits =
182 FakeUrbg<uint64_t, 0, 0xffffffffffffffff, 0x123456780fedcba9>;
183
TEST(FastUniformBitsTest,OutputsUpTo32Bits)184 TEST(FastUniformBitsTest, OutputsUpTo32Bits) {
185 // Tests that how values are composed; the single-bit deltas should be spread
186 // across each invocation.
187 Urng1_5bit urng1_5;
188 Urng4bits urng4;
189 Urng22bits urng22;
190 Urng31bits urng31;
191 Urng32bits urng32;
192 Urng33bits urng33;
193 Urng63bits urng63;
194 Urng64bits urng64;
195
196 // 8-bit types
197 {
198 FastUniformBits<uint8_t> fast8;
199 EXPECT_EQ(0x0, fast8(urng1_5));
200 EXPECT_EQ(0x11, fast8(urng4));
201 EXPECT_EQ(0x20, fast8(urng22));
202 EXPECT_EQ(0x2, fast8(urng31));
203 EXPECT_EQ(0x1, fast8(urng32));
204 EXPECT_EQ(0x32, fast8(urng33));
205 EXPECT_EQ(0x77, fast8(urng63));
206 EXPECT_EQ(0xa9, fast8(urng64));
207 }
208
209 // 16-bit types
210 {
211 FastUniformBits<uint16_t> fast16;
212 EXPECT_EQ(0x0, fast16(urng1_5));
213 EXPECT_EQ(0x1111, fast16(urng4));
214 EXPECT_EQ(0x1020, fast16(urng22));
215 EXPECT_EQ(0x0f02, fast16(urng31));
216 EXPECT_EQ(0x0f01, fast16(urng32));
217 EXPECT_EQ(0x1032, fast16(urng33));
218 EXPECT_EQ(0x5677, fast16(urng63));
219 EXPECT_EQ(0xcba9, fast16(urng64));
220 }
221
222 // 32-bit types
223 {
224 FastUniformBits<uint32_t> fast32;
225 EXPECT_EQ(0x0, fast32(urng1_5));
226 EXPECT_EQ(0x11111111, fast32(urng4));
227 EXPECT_EQ(0x08301020, fast32(urng22));
228 EXPECT_EQ(0x0f020f02, fast32(urng31));
229 EXPECT_EQ(0x74010f01, fast32(urng32));
230 EXPECT_EQ(0x13301032, fast32(urng33));
231 EXPECT_EQ(0x12345677, fast32(urng63));
232 EXPECT_EQ(0x0fedcba9, fast32(urng64));
233 }
234 }
235
TEST(FastUniformBitsTest,Outputs64Bits)236 TEST(FastUniformBitsTest, Outputs64Bits) {
237 // Tests that how values are composed; the single-bit deltas should be spread
238 // across each invocation.
239 FastUniformBits<uint64_t> fast64;
240
241 {
242 FakeUrbg<uint8_t, 0, 1, 0> urng0;
243 FakeUrbg<uint8_t, 0, 1, 1> urng1;
244 Urng4bits urng4;
245 Urng22bits urng22;
246 Urng31bits urng31;
247 Urng32bits urng32;
248 Urng33bits urng33;
249 Urng63bits urng63;
250 Urng64bits urng64;
251
252 // somewhat degenerate cases only create a single bit.
253 EXPECT_EQ(0x0, fast64(urng0));
254 EXPECT_EQ(64, urng0.calls);
255 EXPECT_EQ(0xffffffffffffffff, fast64(urng1));
256 EXPECT_EQ(64, urng1.calls);
257
258 // less degenerate cases.
259 EXPECT_EQ(0x1111111111111111, fast64(urng4));
260 EXPECT_EQ(16, urng4.calls);
261 EXPECT_EQ(0x01020c0408301020, fast64(urng22));
262 EXPECT_EQ(3, urng22.calls);
263 EXPECT_EQ(0x387811c3c0870f02, fast64(urng31));
264 EXPECT_EQ(3, urng31.calls);
265 EXPECT_EQ(0x74010f0174010f01, fast64(urng32));
266 EXPECT_EQ(2, urng32.calls);
267 EXPECT_EQ(0x808194040cb01032, fast64(urng33));
268 EXPECT_EQ(3, urng33.calls);
269 EXPECT_EQ(0x1234567712345677, fast64(urng63));
270 EXPECT_EQ(2, urng63.calls);
271 EXPECT_EQ(0x123456780fedcba9, fast64(urng64));
272 EXPECT_EQ(1, urng64.calls);
273 }
274
275 // The 1.5 bit case is somewhat interesting in that the algorithm refinement
276 // causes one extra small sample. Comments here reference the names used in
277 // [rand.adapt.ibits] that correspond to this case.
278 {
279 Urng1_5bit urng1_5;
280
281 // w = 64
282 // R = 3
283 // m = 1
284 // n' = 64
285 // w0' = 1
286 // y0' = 2
287 // n = (1 <= 0) > 64 : 65 = 65
288 // n0 = 65 - (64%65) = 1
289 // n1 = 64
290 // w0 = 0
291 // y0 = 3
292 // w1 = 1
293 // y1 = 2
294 EXPECT_EQ(0x0, fast64(urng1_5));
295 EXPECT_EQ(65, urng1_5.calls);
296 }
297
298 // Validate rejections for non-power-of-2 cases.
299 {
300 Urng1_5bit urng1_5(true);
301 Urng31bits urng31(true);
302 Urng33bits urng33(true);
303 Urng63bits urng63(true);
304
305 // For 1.5 bits, there would be 1+2*64, except the first
306 // value was accepted and shifted off the end.
307 EXPECT_EQ(0, fast64(urng1_5));
308 EXPECT_EQ(128, urng1_5.calls);
309 EXPECT_EQ(0x387811c3c0870f02, fast64(urng31));
310 EXPECT_EQ(6, urng31.calls);
311 EXPECT_EQ(0x808194040cb01032, fast64(urng33));
312 EXPECT_EQ(6, urng33.calls);
313 EXPECT_EQ(0x1234567712345677, fast64(urng63));
314 EXPECT_EQ(4, urng63.calls);
315 }
316 }
317
TEST(FastUniformBitsTest,URBG32bitRegression)318 TEST(FastUniformBitsTest, URBG32bitRegression) {
319 // Validate with deterministic 32-bit std::minstd_rand
320 // to ensure that operator() performs as expected.
321
322 EXPECT_EQ(2147483646, RangeSize<std::minstd_rand>());
323 EXPECT_EQ(30, IntegerLog2(RangeSize<std::minstd_rand>()));
324
325 std::minstd_rand gen(1);
326 FastUniformBits<uint64_t> fast64;
327
328 EXPECT_EQ(0x05e47095f8791f45, fast64(gen));
329 EXPECT_EQ(0x028be17e3c07c122, fast64(gen));
330 EXPECT_EQ(0x55d2847c1626e8c2, fast64(gen));
331 }
332
333 } // namespace
334 } // namespace random_internal
335 ABSL_NAMESPACE_END
336 } // namespace absl
337