pow10_helper_test.cc
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1 // Copyright 2018 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 
16 
17 #include <cmath>
18 
19 #include "gtest/gtest.h"
21 
22 namespace absl {
23 namespace strings_internal {
24 
25 namespace {
26 
27 struct TestCase {
28  int power; // Testing Pow10(power)
29  uint64_t significand; // Raw bits of the expected value
30  int radix; // significand is adjusted by 2^radix
31 };
32 
33 TEST(Pow10HelperTest, Works) {
34  // The logic in pow10_helper.cc is so simple that theoretically we don't even
35  // need a test. However, we're paranoid and believe that there may be
36  // compilers that don't round floating-point literals correctly, even though
37  // it is specified by the standard. We check various edge cases, just to be
38  // sure.
39  constexpr TestCase kTestCases[] = {
40  // Subnormals
41  {-323, 0x2, -1074},
42  {-322, 0x14, -1074},
43  {-321, 0xca, -1074},
44  {-320, 0x7e8, -1074},
45  {-319, 0x4f10, -1074},
46  {-318, 0x316a2, -1074},
47  {-317, 0x1ee257, -1074},
48  {-316, 0x134d761, -1074},
49  {-315, 0xc1069cd, -1074},
50  {-314, 0x78a42205, -1074},
51  {-313, 0x4b6695433, -1074},
52  {-312, 0x2f201d49fb, -1074},
53  {-311, 0x1d74124e3d1, -1074},
54  {-310, 0x12688b70e62b, -1074},
55  {-309, 0xb8157268fdaf, -1074},
56  {-308, 0x730d67819e8d2, -1074},
57  // Values that are very close to rounding the other way.
58  // Comment shows difference of significand from the true value.
59  {-307, 0x11fa182c40c60d, -1072}, // -.4588
60  {-290, 0x18f2b061aea072, -1016}, // .4854
61  {-276, 0x11BA03F5B21000, -969}, // .4709
62  {-259, 0x1899C2F6732210, -913}, // .4830
63  {-252, 0x1D53844EE47DD1, -890}, // -.4743
64  {-227, 0x1E5297287C2F45, -807}, // -.4708
65  {-198, 0x1322E220A5B17E, -710}, // -.4714
66  {-195, 0x12B010D3E1CF56, -700}, // .4928
67  {-192, 0x123FF06EEA847A, -690}, // .4968
68  {-163, 0x1708D0F84D3DE7, -594}, // -.4977
69  {-145, 0x13FAAC3E3FA1F3, -534}, // -.4785
70  {-111, 0x133D4032C2C7F5, -421}, // .4774
71  {-106, 0x1D5B561574765B, -405}, // -.4869
72  {-104, 0x16EF5B40C2FC77, -398}, // -.4741
73  {-88, 0x197683DF2F268D, -345}, // -.4738
74  {-86, 0x13E497065CD61F, -338}, // .4736
75  {-76, 0x17288E1271F513, -305}, // -.4761
76  {-63, 0x1A53FC9631D10D, -262}, // .4929
77  {-30, 0x14484BFEEBC2A0, -152}, // .4758
78  {-21, 0x12E3B40A0E9B4F, -122}, // -.4916
79  {-5, 0x14F8B588E368F1, -69}, // .4829
80  {23, 0x152D02C7E14AF6, 24}, // -.5000 (exactly, round-to-even)
81  {29, 0x1431E0FAE6D721, 44}, // -.4870
82  {34, 0x1ED09BEAD87C03, 60}, // -.4721
83  {70, 0x172EBAD6DDC73D, 180}, // .4733
84  {105, 0x1BE7ABD3781ECA, 296}, // -.4850
85  {126, 0x17A2ECC414A03F, 366}, // -.4999
86  {130, 0x1CDA62055B2D9E, 379}, // .4855
87  {165, 0x115D847AD00087, 496}, // -.4913
88  {172, 0x14B378469B6732, 519}, // .4818
89  {187, 0x1262DFEEBBB0F9, 569}, // -.4805
90  {210, 0x18557F31326BBB, 645}, // -.4992
91  {212, 0x1302CB5E6F642A, 652}, // -.4838
92  {215, 0x1290BA9A38C7D1, 662}, // -.4881
93  {236, 0x1F736F9B3494E9, 731}, // .4707
94  {244, 0x176EC98994F489, 758}, // .4924
95  {250, 0x1658E3AB795204, 778}, // -.4963
96  {252, 0x117571DDF6C814, 785}, // .4873
97  {254, 0x1B4781EAD1989E, 791}, // -.4887
98  {260, 0x1A03FDE214CAF1, 811}, // .4784
99  {284, 0x1585041B2C477F, 891}, // .4798
100  {304, 0x1D2A1BE4048F90, 957}, // -.4987
101  // Out-of-range values
102  {-324, 0x0, 0},
103  {-325, 0x0, 0},
104  {-326, 0x0, 0},
105  {309, 1, 2000},
106  {310, 1, 2000},
107  {311, 1, 2000},
108  };
109  for (const TestCase& test_case : kTestCases) {
110  EXPECT_EQ(Pow10(test_case.power),
111  std::ldexp(test_case.significand, test_case.radix))
112  << absl::StrFormat("Failure for Pow10(%d): %a vs %a", test_case.power,
113  Pow10(test_case.power),
114  std::ldexp(test_case.significand, test_case.radix));
115  }
116 }
117 
118 } // namespace
119 } // namespace strings_internal
120 } // namespace absl
double Pow10(int exp)
uint64_t significand
int power
Definition: algorithm.h:29
ABSL_MUST_USE_RESULT std::string StrFormat(const FormatSpec< Args... > &format, const Args &...args)
Definition: str_format.h:305
TEST(BigUnsigned, ShiftLeft)
int radix


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autogenerated on Wed Jun 19 2019 19:19:57