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Add self-test that reveals SkChecksum weakness

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Review URL: https://codereview.appspot.com/6845064

git-svn-id: http://skia.googlecode.com/svn/trunk@6535 2bbb7eff-a529-9590-31e7-b0007b416f81
This commit is contained in:
epoger@google.com 2012-11-21 19:04:17 +00:00
parent 44737654c3
commit f74dd16e9a
1 changed files with 43 additions and 14 deletions
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57
tests/ChecksumTest.cpp
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@ -68,7 +68,8 @@ namespace skiatest {
// Try checksums of different-sized chunks, but always
// 32-bit aligned and big enough to contain all the
// nonzero bytes.
// 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);
@ -80,25 +81,37 @@ namespace skiatest {
}
}
// Return the checksum of a portion of this static test data
// (8 bytes repeated twice): "1234567812345678"
uint32_t GetTestDataChecksum(size_t offset, size_t len) {
static char testbytes[] = "1234567812345678";
uint32_t* ptr = reinterpret_cast<uint32_t*>(testbytes);
return ComputeChecksum(ptr, len);
// 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(0, 8) ==
GetTestDataChecksum(8, 8));
GetTestDataChecksum(8, 0) ==
GetTestDataChecksum(8, 0));
REPORTER_ASSERT(fReporter,
GetTestDataChecksum(8, 0) !=
GetTestDataChecksum(8, 1));
TestChecksumSelfConsistency(128);
fWhichAlgorithm = kSkConsistentChecksum;
REPORTER_ASSERT(fReporter,
GetTestDataChecksum(0, 8) ==
GetTestDataChecksum(8, 8));
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
@ -107,9 +120,25 @@ namespace skiatest {
REPORTER_ASSERT(fReporter, ComputeChecksum(NULL, 0) == 0);
fWhichAlgorithm = kSkConsistentChecksum;
REPORTER_ASSERT(fReporter, ComputeChecksum(NULL, 0) == 0);
REPORTER_ASSERT(fReporter, GetTestDataChecksum(0, 8) == 0xa12fac2c);
REPORTER_ASSERT(fReporter, GetTestDataChecksum(8, 8) == 0xa12fac2c);
REPORTER_ASSERT(fReporter, GetTestDataChecksum(8, 4) == 0x34333231);
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;