3c2d32b8e2
Reason for revert: gotta put back *compute = 0. Original issue's description: > Switch uses of SkChecksum::Compute to Murmur3. > > SkChecksum::Compute is a very, very poorly distributed hash function. > This replaces all remaining uses with Murmur3. > > The only interesting stuff is in src/gpu. > > BUG=skia: > > Committed: https://skia.googlesource.com/skia/+/1d024a3c909ae5cefa5e8b339e2b52dc73ee85ac > > Committed: https://skia.googlesource.com/skia/+/540e95483d285b555e9b1a73d18c16e7d7c0deba TBR=bsalomon@google.com,mtklein@chromium.org NOPRESUBMIT=true NOTREECHECKS=true NOTRY=true BUG=skia: Review URL: https://codereview.chromium.org/1448023005
66 lines
2.3 KiB
C++
66 lines
2.3 KiB
C++
/*
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* Copyright 2012 Google Inc.
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*
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* Use of this source code is governed by a BSD-style license that can be
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* found in the LICENSE file.
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*/
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#include "SkChecksum.h"
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#include "SkRandom.h"
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#include "Test.h"
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// Murmur3 has an optional third seed argument, so we wrap it to fit a uniform type.
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static uint32_t murmur_noseed(const uint32_t* d, size_t l) { return SkChecksum::Murmur3(d, l); }
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#define ASSERT(x) REPORTER_ASSERT(r, x)
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DEF_TEST(Checksum, r) {
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// Algorithms to test. They're currently all uint32_t(const uint32_t*, size_t).
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typedef uint32_t(*algorithmProc)(const uint32_t*, size_t);
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const algorithmProc kAlgorithms[] = { &SkChecksum::Compute, &murmur_noseed };
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// Put 128 random bytes into two identical buffers. Any multiple of 4 will do.
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const size_t kBytes = SkAlign4(128);
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SkRandom rand;
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uint32_t data[kBytes/4], tweaked[kBytes/4];
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for (size_t i = 0; i < SK_ARRAY_COUNT(tweaked); ++i) {
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data[i] = tweaked[i] = rand.nextU();
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}
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// Test each algorithm.
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for (size_t i = 0; i < SK_ARRAY_COUNT(kAlgorithms); ++i) {
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const algorithmProc algorithm = kAlgorithms[i];
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// Hash of nullptr is always 0.
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ASSERT(algorithm(nullptr, 0) == 0);
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const uint32_t hash = algorithm(data, kBytes);
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// Should be deterministic.
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ASSERT(hash == algorithm(data, kBytes));
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// Changing any single element should change the hash.
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for (size_t j = 0; j < SK_ARRAY_COUNT(tweaked); ++j) {
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const uint32_t saved = tweaked[j];
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tweaked[j] = rand.nextU();
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const uint32_t tweakedHash = algorithm(tweaked, kBytes);
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ASSERT(tweakedHash != hash);
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ASSERT(tweakedHash == algorithm(tweaked, kBytes));
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tweaked[j] = saved;
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}
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}
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}
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DEF_TEST(GoodHash, r) {
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ASSERT(SkGoodHash()(( int32_t)4) == 614249093); // 4 bytes. Hits SkChecksum::Mix fast path.
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ASSERT(SkGoodHash()((uint32_t)4) == 614249093); // (Ditto)
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// None of these are 4 byte sized, so they use SkChecksum::Murmur3, not SkChecksum::Mix.
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ASSERT(SkGoodHash()((uint64_t)4) == 3491892518);
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ASSERT(SkGoodHash()((uint16_t)4) == 899251846);
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ASSERT(SkGoodHash()( (uint8_t)4) == 962700458);
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// Tests SkString is correctly specialized.
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ASSERT(SkGoodHash()(SkString("Hi")) == 55667557);
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}
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