1
2/*
3 * Copyright 2012 Google Inc.
4 *
5 * Use of this source code is governed by a BSD-style license that can be
6 * found in the LICENSE file.
7 */
8#include "Test.h"
9
10#include "SkChecksum.h"
11
12// Word size that is large enough to hold results of any checksum type.
13typedef uint64_t checksum_result;
14
15namespace skiatest {
16    class ChecksumTestClass : public Test {
17    public:
18        static Test* Factory(void*) {return SkNEW(ChecksumTestClass); }
19    protected:
20        virtual void onGetName(SkString* name) { name->set("Checksum"); }
21        virtual void onRun(Reporter* reporter) {
22            this->fReporter = reporter;
23            RunTest();
24        }
25    private:
26        enum Algorithm {
27            kSkChecksum,
28            kMurmur3,
29        };
30
31        // Call Compute(data, size) on the appropriate checksum algorithm,
32        // depending on this->fWhichAlgorithm.
33        checksum_result ComputeChecksum(const char *data, size_t size) {
34            switch(fWhichAlgorithm) {
35            case kSkChecksum:
36                REPORTER_ASSERT_MESSAGE(fReporter,
37                                        reinterpret_cast<uintptr_t>(data) % 4 == 0,
38                                        "test data pointer is not 32-bit aligned");
39                REPORTER_ASSERT_MESSAGE(fReporter, SkIsAlign4(size),
40                                        "test data size is not 32-bit aligned");
41                return SkChecksum::Compute(reinterpret_cast<const uint32_t *>(data), size);
42            case kMurmur3:
43                REPORTER_ASSERT_MESSAGE(fReporter,
44                                        reinterpret_cast<uintptr_t>(data) % 4 == 0,
45                                        "test data pointer is not 32-bit aligned");
46                REPORTER_ASSERT_MESSAGE(fReporter, SkIsAlign4(size),
47                                        "test data size is not 32-bit aligned");
48                return SkChecksum::Murmur3(reinterpret_cast<const uint32_t *>(data), size);
49            default:
50                SkString message("fWhichAlgorithm has unknown value ");
51                message.appendf("%d", fWhichAlgorithm);
52                fReporter->reportFailed(message);
53            }
54            // we never get here
55            return 0;
56        }
57
58        // Confirm that the checksum algorithm (specified by fWhichAlgorithm)
59        // generates the same results if called twice over the same data.
60        void TestChecksumSelfConsistency(size_t buf_size) {
61            SkAutoMalloc storage(buf_size);
62            char* ptr = reinterpret_cast<char *>(storage.get());
63
64            REPORTER_ASSERT(fReporter,
65                            GetTestDataChecksum(8, 0) ==
66                            GetTestDataChecksum(8, 0));
67            REPORTER_ASSERT(fReporter,
68                            GetTestDataChecksum(8, 0) !=
69                            GetTestDataChecksum(8, 1));
70
71            sk_bzero(ptr, buf_size);
72            checksum_result prev = 0;
73
74            // assert that as we change values (from 0 to non-zero) in
75            // our buffer, we get a different value
76            for (size_t i = 0; i < buf_size; ++i) {
77                ptr[i] = (i & 0x7f) + 1; // need some non-zero value here
78
79                // Try checksums of different-sized chunks, but always
80                // 32-bit aligned and big enough to contain all the
81                // nonzero bytes.  (Remaining bytes will still be zero
82                // from the initial sk_bzero() call.)
83                size_t checksum_size = (((i/4)+1)*4);
84                REPORTER_ASSERT(fReporter, checksum_size <= buf_size);
85
86                checksum_result curr = ComputeChecksum(ptr, checksum_size);
87                REPORTER_ASSERT(fReporter, prev != curr);
88                checksum_result again = ComputeChecksum(ptr, checksum_size);
89                REPORTER_ASSERT(fReporter, again == curr);
90                prev = curr;
91            }
92        }
93
94        // Return the checksum of a buffer of bytes 'len' long.
95        // The pattern of values within the buffer will be consistent
96        // for every call, based on 'seed'.
97        checksum_result GetTestDataChecksum(size_t len, char seed=0) {
98            SkAutoMalloc storage(len);
99            char* start = reinterpret_cast<char *>(storage.get());
100            char* ptr = start;
101            for (size_t i = 0; i < len; ++i) {
102                *ptr++ = ((seed+i) & 0x7f);
103            }
104            checksum_result result = ComputeChecksum(start, len);
105            return result;
106        }
107
108        void RunTest() {
109            const Algorithm algorithms[] = { kSkChecksum, kMurmur3 };
110            for (size_t i = 0; i < SK_ARRAY_COUNT(algorithms); i++) {
111                fWhichAlgorithm = algorithms[i];
112
113                // Test self-consistency of checksum algorithms.
114                TestChecksumSelfConsistency(128);
115
116                // Test checksum results that should be consistent across
117                // versions and platforms.
118                REPORTER_ASSERT(fReporter, ComputeChecksum(NULL, 0) == 0);
119
120                const bool colision1 = GetTestDataChecksum(128) == GetTestDataChecksum(256);
121                const bool colision2 = GetTestDataChecksum(132) == GetTestDataChecksum(260);
122                if (fWhichAlgorithm == kSkChecksum) {
123                    // TODO: note the weakness exposed by these collisions...
124                    // We need to improve the SkChecksum algorithm.
125                    // We would prefer that these asserts FAIL!
126                    // Filed as https://code.google.com/p/skia/issues/detail?id=981
127                    // ('SkChecksum algorithm allows for way too many collisions')
128                    REPORTER_ASSERT(fReporter, colision1);
129                    REPORTER_ASSERT(fReporter, colision2);
130                } else {
131                    REPORTER_ASSERT(fReporter, !colision1);
132                    REPORTER_ASSERT(fReporter, !colision2);
133                }
134            }
135        }
136
137        Reporter* fReporter;
138        Algorithm fWhichAlgorithm;
139    };
140
141    static TestRegistry gReg(ChecksumTestClass::Factory);
142}
143