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
15 #include "absl/strings/internal/pow10_helper.h"
16
17 #include <cmath>
18
19 #include "gtest/gtest.h"
20 #include "absl/strings/str_format.h"
21
22 namespace absl {
23 ABSL_NAMESPACE_BEGIN
24 namespace strings_internal {
25
26 namespace {
27
28 struct TestCase {
29 int power; // Testing Pow10(power)
30 uint64_t significand; // Raw bits of the expected value
31 int radix; // significand is adjusted by 2^radix
32 };
33
TEST(Pow10HelperTest,Works)34 TEST(Pow10HelperTest, Works) {
35 // The logic in pow10_helper.cc is so simple that theoretically we don't even
36 // need a test. However, we're paranoid and believe that there may be
37 // compilers that don't round floating-point literals correctly, even though
38 // it is specified by the standard. We check various edge cases, just to be
39 // sure.
40 constexpr TestCase kTestCases[] = {
41 // Subnormals
42 {-323, 0x2, -1074},
43 {-322, 0x14, -1074},
44 {-321, 0xca, -1074},
45 {-320, 0x7e8, -1074},
46 {-319, 0x4f10, -1074},
47 {-318, 0x316a2, -1074},
48 {-317, 0x1ee257, -1074},
49 {-316, 0x134d761, -1074},
50 {-315, 0xc1069cd, -1074},
51 {-314, 0x78a42205, -1074},
52 {-313, 0x4b6695433, -1074},
53 {-312, 0x2f201d49fb, -1074},
54 {-311, 0x1d74124e3d1, -1074},
55 {-310, 0x12688b70e62b, -1074},
56 {-309, 0xb8157268fdaf, -1074},
57 {-308, 0x730d67819e8d2, -1074},
58 // Values that are very close to rounding the other way.
59 // Comment shows difference of significand from the true value.
60 {-307, 0x11fa182c40c60d, -1072}, // -.4588
61 {-290, 0x18f2b061aea072, -1016}, // .4854
62 {-276, 0x11BA03F5B21000, -969}, // .4709
63 {-259, 0x1899C2F6732210, -913}, // .4830
64 {-252, 0x1D53844EE47DD1, -890}, // -.4743
65 {-227, 0x1E5297287C2F45, -807}, // -.4708
66 {-198, 0x1322E220A5B17E, -710}, // -.4714
67 {-195, 0x12B010D3E1CF56, -700}, // .4928
68 {-192, 0x123FF06EEA847A, -690}, // .4968
69 {-163, 0x1708D0F84D3DE7, -594}, // -.4977
70 {-145, 0x13FAAC3E3FA1F3, -534}, // -.4785
71 {-111, 0x133D4032C2C7F5, -421}, // .4774
72 {-106, 0x1D5B561574765B, -405}, // -.4869
73 {-104, 0x16EF5B40C2FC77, -398}, // -.4741
74 {-88, 0x197683DF2F268D, -345}, // -.4738
75 {-86, 0x13E497065CD61F, -338}, // .4736
76 {-76, 0x17288E1271F513, -305}, // -.4761
77 {-63, 0x1A53FC9631D10D, -262}, // .4929
78 {-30, 0x14484BFEEBC2A0, -152}, // .4758
79 {-21, 0x12E3B40A0E9B4F, -122}, // -.4916
80 {-5, 0x14F8B588E368F1, -69}, // .4829
81 {23, 0x152D02C7E14AF6, 24}, // -.5000 (exactly, round-to-even)
82 {29, 0x1431E0FAE6D721, 44}, // -.4870
83 {34, 0x1ED09BEAD87C03, 60}, // -.4721
84 {70, 0x172EBAD6DDC73D, 180}, // .4733
85 {105, 0x1BE7ABD3781ECA, 296}, // -.4850
86 {126, 0x17A2ECC414A03F, 366}, // -.4999
87 {130, 0x1CDA62055B2D9E, 379}, // .4855
88 {165, 0x115D847AD00087, 496}, // -.4913
89 {172, 0x14B378469B6732, 519}, // .4818
90 {187, 0x1262DFEEBBB0F9, 569}, // -.4805
91 {210, 0x18557F31326BBB, 645}, // -.4992
92 {212, 0x1302CB5E6F642A, 652}, // -.4838
93 {215, 0x1290BA9A38C7D1, 662}, // -.4881
94 {236, 0x1F736F9B3494E9, 731}, // .4707
95 {244, 0x176EC98994F489, 758}, // .4924
96 {250, 0x1658E3AB795204, 778}, // -.4963
97 {252, 0x117571DDF6C814, 785}, // .4873
98 {254, 0x1B4781EAD1989E, 791}, // -.4887
99 {260, 0x1A03FDE214CAF1, 811}, // .4784
100 {284, 0x1585041B2C477F, 891}, // .4798
101 {304, 0x1D2A1BE4048F90, 957}, // -.4987
102 // Out-of-range values
103 {-324, 0x0, 0},
104 {-325, 0x0, 0},
105 {-326, 0x0, 0},
106 {309, 1, 2000},
107 {310, 1, 2000},
108 {311, 1, 2000},
109 };
110 for (const TestCase& test_case : kTestCases) {
111 EXPECT_EQ(Pow10(test_case.power),
112 std::ldexp(test_case.significand, test_case.radix))
113 << absl::StrFormat("Failure for Pow10(%d): %a vs %a", test_case.power,
114 Pow10(test_case.power),
115 std::ldexp(test_case.significand, test_case.radix));
116 }
117 }
118
119 } // namespace
120 } // namespace strings_internal
121 ABSL_NAMESPACE_END
122 } // namespace absl
123