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
Review URL: https://codereview.chromium.org/1436973003
diff --git a/bench/ChecksumBench.cpp b/bench/ChecksumBench.cpp
index a2c2824..92e7da6 100644
--- a/bench/ChecksumBench.cpp
+++ b/bench/ChecksumBench.cpp
@@ -13,7 +13,6 @@
#include "SkTemplates.h"
enum ChecksumType {
- kChecksum_ChecksumType,
kMD5_ChecksumType,
kSHA1_ChecksumType,
kMurmur3_ChecksumType,
@@ -42,7 +41,6 @@
protected:
const char* onGetName() override {
switch (fType) {
- case kChecksum_ChecksumType: return "compute_checksum";
case kMD5_ChecksumType: return "compute_md5";
case kSHA1_ChecksumType: return "compute_sha1";
case kMurmur3_ChecksumType: return "compute_murmur3";
@@ -53,12 +51,6 @@
void onDraw(int loops, SkCanvas*) override {
switch (fType) {
- case kChecksum_ChecksumType: {
- for (int i = 0; i < loops; i++) {
- volatile uint32_t result = SkChecksum::Compute(fData, sizeof(fData));
- sk_ignore_unused_variable(result);
- }
- } break;
case kMD5_ChecksumType: {
for (int i = 0; i < loops; i++) {
SkMD5 md5;
@@ -91,7 +83,6 @@
///////////////////////////////////////////////////////////////////////////////
-DEF_BENCH( return new ComputeChecksumBench(kChecksum_ChecksumType); )
DEF_BENCH( return new ComputeChecksumBench(kMD5_ChecksumType); )
DEF_BENCH( return new ComputeChecksumBench(kSHA1_ChecksumType); )
DEF_BENCH( return new ComputeChecksumBench(kMurmur3_ChecksumType); )
diff --git a/include/private/SkChecksum.h b/include/private/SkChecksum.h
index 4526416..6289a44 100644
--- a/include/private/SkChecksum.h
+++ b/include/private/SkChecksum.h
@@ -12,31 +12,7 @@
#include "SkTLogic.h"
#include "SkTypes.h"
-/**
- * Computes a 32bit checksum from a blob of 32bit aligned data. This is meant
- * to be very very fast, as it is used internally by the font cache, in
- * conjuction with the entire raw key. This algorithm does not generate
- * unique values as well as others (e.g. MD5) but it performs much faster.
- * Skia's use cases can survive non-unique values (since the entire key is
- * always available). Clients should only be used in circumstances where speed
- * over uniqueness is at a premium.
- */
class SkChecksum : SkNoncopyable {
-private:
- /*
- * Our Rotate and Mash helpers are meant to automatically do the right
- * thing depending if sizeof(uintptr_t) is 4 or 8.
- */
- enum {
- ROTR = 17,
- ROTL = sizeof(uintptr_t) * 8 - ROTR,
- HALFBITS = sizeof(uintptr_t) * 4
- };
-
- static inline uintptr_t Mash(uintptr_t total, uintptr_t value) {
- return ((total >> ROTR) | (total << ROTL)) ^ value;
- }
-
public:
/**
* uint32_t -> uint32_t hash, useful for when you're about to trucate this hash but you
@@ -68,7 +44,6 @@
/**
* Calculate 32-bit Murmur hash (murmur3).
- * This should take 2-3x longer than SkChecksum::Compute, but is a considerably better hash.
* See en.wikipedia.org/wiki/MurmurHash.
*
* @param data Memory address of the data block to be processed.
@@ -77,70 +52,6 @@
* @return hash result
*/
static uint32_t Murmur3(const void* data, size_t bytes, uint32_t seed=0);
-
- /**
- * Compute a 32-bit checksum for a given data block
- *
- * WARNING: this algorithm is tuned for efficiency, not backward/forward
- * compatibility. It may change at any time, so a checksum generated with
- * one version of the Skia code may not match a checksum generated with
- * a different version of the Skia code.
- *
- * @param data Memory address of the data block to be processed. Must be
- * 32-bit aligned.
- * @param size Size of the data block in bytes. Must be a multiple of 4.
- * @return checksum result
- */
- static uint32_t Compute(const uint32_t* data, size_t size) {
- // Use may_alias to remind the compiler we're intentionally violating strict aliasing,
- // and so not to apply strict-aliasing-based optimizations.
- typedef uint32_t SK_ATTRIBUTE(may_alias) aliased_uint32_t;
- const aliased_uint32_t* safe_data = (const aliased_uint32_t*)data;
-
- SkASSERT(SkIsAlign4(size));
-
- /*
- * We want to let the compiler use 32bit or 64bit addressing and math
- * so we use uintptr_t as our magic type. This makes the code a little
- * more obscure (we can't hard-code 32 or 64 anywhere, but have to use
- * sizeof()).
- */
- uintptr_t result = 0;
- const uintptr_t* ptr = reinterpret_cast<const uintptr_t*>(safe_data);
-
- /*
- * count the number of quad element chunks. This takes into account
- * if we're on a 32bit or 64bit arch, since we use sizeof(uintptr_t)
- * to compute how much to shift-down the size.
- */
- size_t n4 = size / (sizeof(uintptr_t) << 2);
- for (size_t i = 0; i < n4; ++i) {
- result = Mash(result, *ptr++);
- result = Mash(result, *ptr++);
- result = Mash(result, *ptr++);
- result = Mash(result, *ptr++);
- }
- size &= ((sizeof(uintptr_t) << 2) - 1);
-
- safe_data = reinterpret_cast<const aliased_uint32_t*>(ptr);
- const aliased_uint32_t* stop = safe_data + (size >> 2);
- while (safe_data < stop) {
- result = Mash(result, *safe_data++);
- }
-
- /*
- * smash us down to 32bits if we were 64. Note that when uintptr_t is
- * 32bits, this code-path should go away, but I still got a warning
- * when I wrote
- * result ^= result >> 32;
- * since >>32 is undefined for 32bit ints, hence the wacky HALFBITS
- * define.
- */
- if (8 == sizeof(result)) {
- result ^= result >> HALFBITS;
- }
- return static_cast<uint32_t>(result);
- }
};
// SkGoodHash should usually be your first choice in hashing data.
diff --git a/src/core/SkPictureFlat.h b/src/core/SkPictureFlat.h
index 98a43ec..8befca0 100644
--- a/src/core/SkPictureFlat.h
+++ b/src/core/SkPictureFlat.h
@@ -179,7 +179,7 @@
class SkFlatController : public SkRefCnt {
public:
-
+
SkFlatController(uint32_t writeBufferFlags = 0);
virtual ~SkFlatController();
@@ -357,7 +357,7 @@
fIndex = index;
fFlatSize = size;
fTopBot[0] = SK_ScalarNaN; // Mark as unwritten.
- fChecksum = SkChecksum::Compute((uint32_t*)this->data(), size);
+ fChecksum = SkChecksum::Murmur3(this->data(), size);
}
int fIndex;
diff --git a/src/gpu/GrProgramDesc.h b/src/gpu/GrProgramDesc.h
index 05b52cc..1510630 100644
--- a/src/gpu/GrProgramDesc.h
+++ b/src/gpu/GrProgramDesc.h
@@ -107,8 +107,8 @@
*(this->atOffset<uint32_t, GrProgramDesc::kLengthOffset>()) = SkToU32(keyLength);
uint32_t* checksum = this->atOffset<uint32_t, GrProgramDesc::kChecksumOffset>();
- *checksum = 0;
- *checksum = SkChecksum::Compute(reinterpret_cast<uint32_t*>(fKey.begin()), keyLength);
+ *checksum = 0; // We'll hash through these bytes, so make sure they're initialized.
+ *checksum = SkChecksum::Murmur3(fKey.begin(), keyLength);
}
// The key, stored in fKey, is composed of four parts:
diff --git a/src/gpu/GrResourceCache.cpp b/src/gpu/GrResourceCache.cpp
index cb6bcf7..4a0c9b2 100644
--- a/src/gpu/GrResourceCache.cpp
+++ b/src/gpu/GrResourceCache.cpp
@@ -42,7 +42,7 @@
}
uint32_t GrResourceKeyHash(const uint32_t* data, size_t size) {
- return SkChecksum::Compute(data, size);
+ return SkChecksum::Murmur3(data, size);
}
//////////////////////////////////////////////////////////////////////////////
@@ -564,7 +564,7 @@
int currP = 0;
int currNP = 0;
while (currP < sortedPurgeableResources.count() &&
- currNP < fNonpurgeableResources.count()) {
+ currNP < fNonpurgeableResources.count()) {
uint32_t tsP = sortedPurgeableResources[currP]->cacheAccess().timestamp();
uint32_t tsNP = fNonpurgeableResources[currNP]->cacheAccess().timestamp();
SkASSERT(tsP != tsNP);
@@ -596,10 +596,10 @@
// count should be the next timestamp we return.
SkASSERT(fTimestamp == SkToU32(count));
-
+
// The historical timestamps of flushes are now invalid.
this->resetFlushTimestamps();
- }
+ }
}
return fTimestamp++;
}
diff --git a/tests/ChecksumTest.cpp b/tests/ChecksumTest.cpp
index c095a5a..cf9d65c 100644
--- a/tests/ChecksumTest.cpp
+++ b/tests/ChecksumTest.cpp
@@ -18,7 +18,7 @@
DEF_TEST(Checksum, r) {
// Algorithms to test. They're currently all uint32_t(const uint32_t*, size_t).
typedef uint32_t(*algorithmProc)(const uint32_t*, size_t);
- const algorithmProc kAlgorithms[] = { &SkChecksum::Compute, &murmur_noseed };
+ const algorithmProc kAlgorithms[] = { &murmur_noseed };
// Put 128 random bytes into two identical buffers. Any multiple of 4 will do.
const size_t kBytes = SkAlign4(128);