tests/ChecksumTest.cpp

/*
 * Copyright 2012 Google Inc.
 *
 * Use of this source code is governed by a BSD-style license that can be
 * found in the LICENSE file.
 */
#include "Test.h"
#include "SkChecksum.h"
#include "SkConsistentChecksum.h"

namespace skiatest {
    class ChecksumTestClass : public Test {
    public:
        static Test* Factory(void*) {return SkNEW(ChecksumTestClass); }
    protected:
        virtual void onGetName(SkString* name) { name->set("Checksum"); }
        virtual void onRun(Reporter* reporter) {
            this->fReporter = reporter;
            RunTest();
        }
    private:
        enum Algorithm {
            kSkChecksum,
            kSkConsistentChecksum
        };

        // Call Compute(data, size) on the appropriate checksum algorithm,
        // depending on this->fWhichAlgorithm.
        uint32_t ComputeChecksum(uint32_t* data, size_t size) {
            // Our checksum algorithms require 32-bit aligned data.
            // If either of these tests fail, then the algorithm
            // doesn't have a chance.
            REPORTER_ASSERT_MESSAGE(fReporter,
                                    reinterpret_cast<uintptr_t>(data) % 4 == 0,
                                    "test data pointer is not 32-bit aligned");
            REPORTER_ASSERT_MESSAGE(fReporter, SkIsAlign4(size),
                                    "test data size is not 32-bit aligned");

            switch(fWhichAlgorithm) {
            case kSkChecksum:
                return SkChecksum::Compute(data, size);
            case kSkConsistentChecksum:
                return SkConsistentChecksum::Compute(data, size);
            default:
                SkString message("fWhichAlgorithm has unknown value ");
                message.appendf("%d", fWhichAlgorithm);
                fReporter->reportFailed(message);
            }
            // we never get here
            return 0;
        }

        // Confirm that the checksum algorithm (specified by fWhichAlgorithm)
        // generates the same results if called twice over the same data.
        void TestChecksumSelfConsistency(size_t buf_size) {
            SkAutoMalloc storage(buf_size);
            uint32_t*    ptr = (uint32_t*)storage.get();
            char*        cptr = (char*)ptr;

            sk_bzero(ptr, buf_size);
            uint32_t prev = 0;

            // assert that as we change values (from 0 to non-zero) in
            // our buffer, we get a different value
            for (size_t i = 0; i < buf_size; ++i) {
                cptr[i] = (i & 0x7f) + 1; // need some non-zero value here

                // Try checksums of different-sized chunks, but always
                // 32-bit aligned and big enough to contain all the
                // nonzero bytes.  (Remaining bytes will still be zero
                // from the initial sk_bzero() call.)
                size_t checksum_size = (((i/4)+1)*4);
                REPORTER_ASSERT(fReporter, checksum_size <= buf_size);

                uint32_t curr = ComputeChecksum(ptr, checksum_size);
                REPORTER_ASSERT(fReporter, prev != curr);
                uint32_t again = ComputeChecksum(ptr, checksum_size);
                REPORTER_ASSERT(fReporter, again == curr);
                prev = curr;
            }
        }

        // Return the checksum of a buffer of bytes 'len' long.
        // The pattern of values within the buffer will be consistent
        // for every call, based on 'seed'.
        uint32_t GetTestDataChecksum(size_t len, char seed=0) {
            SkAutoMalloc storage(len);
            uint32_t* start = (uint32_t *)storage.get();
            char* ptr = (char *)start;
            for (size_t i = 0; i < len; ++i) {
                *ptr++ = ((seed+i) & 0x7f);
            }
            uint32_t result = ComputeChecksum(start, len);
            return result;
        }

        void RunTest() {
            // Test self-consistency of checksum algorithms.
            fWhichAlgorithm = kSkChecksum;
            REPORTER_ASSERT(fReporter,
                            GetTestDataChecksum(8, 0) ==
                            GetTestDataChecksum(8, 0));
            REPORTER_ASSERT(fReporter,
                            GetTestDataChecksum(8, 0) !=
                            GetTestDataChecksum(8, 1));
            TestChecksumSelfConsistency(128);
            fWhichAlgorithm = kSkConsistentChecksum;
            REPORTER_ASSERT(fReporter,
                            GetTestDataChecksum(8, 0) ==
                            GetTestDataChecksum(8, 0));
            REPORTER_ASSERT(fReporter,
                            GetTestDataChecksum(8, 0) !=
                            GetTestDataChecksum(8, 1));
            TestChecksumSelfConsistency(128);

            // Test checksum results that should be consistent across
            // versions and platforms.
            fWhichAlgorithm = kSkChecksum;
            REPORTER_ASSERT(fReporter, ComputeChecksum(NULL, 0) == 0);
            fWhichAlgorithm = kSkConsistentChecksum;
            REPORTER_ASSERT(fReporter, ComputeChecksum(NULL, 0) == 0);
            REPORTER_ASSERT(fReporter, GetTestDataChecksum(4)  == 0x03020100);
            REPORTER_ASSERT(fReporter, GetTestDataChecksum(8)  == 0x07860485);

            // TODO: note the weakness exposed by these collisions...
            // We need to improve the SkConsistentChecksum algorithm
            // (and maybe SkChecksum too?)
            // We would prefer that these asserts FAIL!
            // Filed as https://code.google.com/p/skia/issues/detail?id=981
            // ('SkChecksum algorithm allows for way too many collisions')
            fWhichAlgorithm = kSkChecksum;
            REPORTER_ASSERT(fReporter,
                GetTestDataChecksum(128) == GetTestDataChecksum(256));
            REPORTER_ASSERT(fReporter,
                GetTestDataChecksum(132) == GetTestDataChecksum(260));
            fWhichAlgorithm = kSkConsistentChecksum;
            REPORTER_ASSERT(fReporter, GetTestDataChecksum(128) == 0);
            REPORTER_ASSERT(fReporter, GetTestDataChecksum(132) == 0x03020100);
            REPORTER_ASSERT(fReporter, GetTestDataChecksum(256) == 0);
            REPORTER_ASSERT(fReporter, GetTestDataChecksum(260) == 0x03020100);
        }

        Reporter* fReporter;
        Algorithm fWhichAlgorithm;
    };

    static TestRegistry gReg(ChecksumTestClass::Factory);
}