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-rw-r--r--gyp/tests.gypi1
-rw-r--r--include/core/SkTemplates.h5
-rw-r--r--src/core/SkTHash.h206
-rw-r--r--tests/HashTest.cpp57
4 files changed, 269 insertions, 0 deletions
diff --git a/gyp/tests.gypi b/gyp/tests.gypi
index e1a9a37609..25e1b7ae8c 100644
--- a/gyp/tests.gypi
+++ b/gyp/tests.gypi
@@ -117,6 +117,7 @@
'../tests/GrTBSearchTest.cpp',
'../tests/GrTRecorderTest.cpp',
'../tests/GradientTest.cpp',
+ '../tests/HashTest.cpp',
'../tests/ImageCacheTest.cpp',
'../tests/ImageDecodingTest.cpp',
'../tests/ImageFilterTest.cpp',
diff --git a/include/core/SkTemplates.h b/include/core/SkTemplates.h
index c26e4422b5..b18556b452 100644
--- a/include/core/SkTemplates.h
+++ b/include/core/SkTemplates.h
@@ -254,6 +254,11 @@ public:
return fArray[index];
}
+ void swap(SkAutoTArray& other) {
+ SkTSwap(fArray, other.fArray);
+ SkDEBUGCODE(SkTSwap(fCount, other.fCount));
+ }
+
private:
T* fArray;
SkDEBUGCODE(int fCount;)
diff --git a/src/core/SkTHash.h b/src/core/SkTHash.h
new file mode 100644
index 0000000000..5e317357ed
--- /dev/null
+++ b/src/core/SkTHash.h
@@ -0,0 +1,206 @@
+#ifndef SkTHash_DEFINED
+#define SkTHash_DEFINED
+
+#include "SkTypes.h"
+#include "SkTemplates.h"
+
+// Before trying to use SkTHashTable, look below to see if SkTHashMap or SkTHashSet works for you.
+// They're easier to use, usually perform the same, and have fewer sharp edges.
+
+// T and K are treated as ordinary copyable C++ types.
+// Traits must have:
+// - static K GetKey(T)
+// - static uint32_t Hash(K)
+// If the key is large and stored inside T, you may want to make K a const&.
+// Similarly, if T is large you might want it to be a pointer.
+template <typename T, typename K, typename Traits = T>
+class SkTHashTable : SkNoncopyable {
+public:
+ SkTHashTable() : fCount(0), fCapacity(0) {}
+
+ // How many entries are in the table?
+ int count() const { return fCount; }
+
+ // !!!!!!!!!!!!!!!!! CAUTION !!!!!!!!!!!!!!!!!
+ // set(), find() and foreach() all allow mutable access to table entries.
+ // If you change an entry so that it no longer has the same key, all hell
+ // will break loose. Do not do that!
+ //
+ // Please prefer to use SkTHashMap or SkTHashSet, which do not have this danger.
+
+ // The pointers returned by set() and find() are valid only until the next call to set().
+ // The pointers you receive in foreach() are only valid for its duration.
+
+ // Copy val into the hash table, returning a pointer to the copy now in the table.
+ // If there already is an entry in the table with the same key, we overwrite it.
+ T* set(T val) {
+ if (4 * fCount >= 3 * fCapacity) {
+ this->resize(fCapacity > 0 ? fCapacity * 2 : 4);
+ }
+ return this->uncheckedSet(val);
+ }
+
+ // If there is an entry in the table with this key, return a pointer to it. If not, NULL.
+ T* find(K key) const {
+ uint32_t hash = Hash(key);
+ int index = hash & (fCapacity-1);
+ for (int n = 0; n < fCapacity; n++) {
+ Slot& s = fSlots[index];
+ if (s.empty()) {
+ return NULL;
+ }
+ if (hash == s.hash && key == Traits::GetKey(s.val)) {
+ return &s.val;
+ }
+ index = this->next(index, n);
+ }
+ SkASSERT(fCapacity == 0);
+ return NULL;
+ }
+
+ // Call fn on every entry in the table. You may mutate the entries, but be very careful.
+ template <typename Arg>
+ void foreach(void(*fn)(T*, Arg), Arg arg) {
+ for (int i = 0; i < fCapacity; i++) {
+ Slot& s = fSlots[i];
+ if (!s.empty()) {
+ fn(&s.val, arg);
+ }
+ }
+ }
+
+private:
+ T* uncheckedSet(T val) {
+ K key = Traits::GetKey(val);
+ uint32_t hash = Hash(key);
+ int index = hash & (fCapacity-1);
+ for (int n = 0; n < fCapacity; n++) {
+ Slot& s = fSlots[index];
+ if (s.empty()) {
+ // New entry.
+ s.val = val;
+ s.hash = hash;
+ fCount++;
+ return &s.val;
+ }
+ if (hash == s.hash && key == Traits::GetKey(s.val)) {
+ // Overwrite previous entry.
+ s.val = val;
+ return &s.val;
+ }
+ index = this->next(index, n);
+ }
+ SkASSERT(false);
+ return NULL;
+ }
+
+ void resize(int capacity) {
+ int oldCapacity = fCapacity;
+ SkDEBUGCODE(int oldCount = fCount);
+
+ fCount = 0;
+ fCapacity = capacity;
+ SkAutoTArray<Slot> oldSlots(capacity);
+ oldSlots.swap(fSlots);
+
+ for (int i = 0; i < oldCapacity; i++) {
+ const Slot& s = oldSlots[i];
+ if (!s.empty()) {
+ this->uncheckedSet(s.val);
+ }
+ }
+ SkASSERT(fCount == oldCount);
+ }
+
+ int next(int index, int n) const {
+ // A valid strategy explores all slots in [0, fCapacity) as n walks from 0 to fCapacity-1.
+ // Both of these strategies are valid:
+ //return (index + 0 + 1) & (fCapacity-1); // Linear probing.
+ return (index + n + 1) & (fCapacity-1); // Quadratic probing.
+ }
+
+ static uint32_t Hash(K key) {
+ uint32_t hash = Traits::Hash(key);
+ return hash == 0 ? 1 : hash; // We reserve hash == 0 to mark empty slots.
+ }
+
+ struct Slot {
+ Slot() : hash(0) {}
+ bool empty() const { return hash == 0; }
+
+ T val;
+ uint32_t hash;
+ };
+
+ int fCount, fCapacity;
+ SkAutoTArray<Slot> fSlots;
+};
+
+// Maps K->V. A more user-friendly wrapper around SkTHashTable, suitable for most use cases.
+// K and V are treated as ordinary copyable C++ types, with no assumed relationship between the two.
+template <typename K, typename V, uint32_t(*HashK)(K)>
+class SkTHashMap : SkNoncopyable {
+public:
+ SkTHashMap() {}
+
+ // How many key/value pairs are in the table?
+ int count() const { return fTable.count(); }
+
+ // N.B. The pointers returned by set() and find() are valid only until the next call to set().
+
+ // Set key to val in the table, replacing any previous value with the same key.
+ // We copy both key and val, and return a pointer to the value copy now in the table.
+ V* set(K key, V val) {
+ Pair in = { key, val };
+ Pair* out = fTable.set(in);
+ return &out->val;
+ }
+
+ // If there is key/value entry in the table with this key, return a pointer to the value.
+ // If not, return NULL.
+ V* find(K key) const {
+ if (Pair* p = fTable.find(key)) {
+ return &p->val;
+ }
+ return NULL;
+ }
+
+ // Call fn on every key/value pair in the table. You may mutate the value but not the key.
+ void foreach(void(*fn)(K, V*)) { fTable.foreach(ForEach, fn); }
+
+private:
+ struct Pair {
+ K key;
+ V val;
+ static K GetKey(Pair p) { return p.key; }
+ static uint32_t Hash(K key) { return HashK(key); }
+ };
+ static void ForEach(Pair* p, void (*fn)(K, V*)) { fn(p->key, &p->val); }
+
+ SkTHashTable<Pair, K> fTable;
+};
+
+// A set of T. T is treated as an ordiary copyable C++ type.
+template <typename T, uint32_t(*HashT)(T)>
+class SkTHashSet : SkNoncopyable {
+public:
+ SkTHashSet() {}
+
+ // How many items are in the set?
+ int count() const { return fTable.count(); }
+
+ // Copy an item into the set.
+ void add(T item) { fTable.set(item); }
+
+ // Is this item in the set?
+ bool contains(T item) const { return SkToBool(fTable.find(item)); }
+
+private:
+ struct Traits {
+ static T GetKey(T item) { return item; }
+ static uint32_t Hash(T item) { return HashT(item); }
+ };
+ SkTHashTable<T, T, Traits> fTable;
+};
+
+#endif//SkTHash_DEFINED
diff --git a/tests/HashTest.cpp b/tests/HashTest.cpp
new file mode 100644
index 0000000000..24032a5ec5
--- /dev/null
+++ b/tests/HashTest.cpp
@@ -0,0 +1,57 @@
+#include "SkChecksum.h"
+#include "SkString.h"
+#include "SkTHash.h"
+#include "Test.h"
+
+namespace { uint32_t hash_int(int k) { return SkChecksum::Mix(k); } }
+
+static void set_negative_key(int key, double* d) { *d = -key; }
+
+DEF_TEST(HashMap, r) {
+ SkTHashMap<int, double, hash_int> map;
+
+ map.set(3, 4.0);
+ REPORTER_ASSERT(r, map.count() == 1);
+
+ double* found = map.find(3);
+ REPORTER_ASSERT(r, found);
+ REPORTER_ASSERT(r, *found == 4.0);
+
+ map.foreach(set_negative_key);
+ found = map.find(3);
+ REPORTER_ASSERT(r, found);
+ REPORTER_ASSERT(r, *found == -3.0);
+
+ REPORTER_ASSERT(r, !map.find(2));
+
+ const int N = 20;
+
+ for (int i = 0; i < N; i++) {
+ map.set(i, 2.0*i);
+ }
+ for (int i = 0; i < N; i++) {
+ double* found = map.find(i);;
+ REPORTER_ASSERT(r, found);
+ REPORTER_ASSERT(r, *found == i*2.0);
+ }
+ for (int i = N; i < 2*N; i++) {
+ REPORTER_ASSERT(r, !map.find(i));
+ }
+
+ REPORTER_ASSERT(r, map.count() == N);
+}
+
+namespace { uint32_t hash_string(SkString s) { return s.size(); } }
+
+DEF_TEST(HashSet, r) {
+ SkTHashSet<SkString, hash_string> set;
+
+ set.add(SkString("Hello"));
+ set.add(SkString("World"));
+
+ REPORTER_ASSERT(r, set.count() == 2);
+
+ REPORTER_ASSERT(r, set.contains(SkString("Hello")));
+ REPORTER_ASSERT(r, set.contains(SkString("World")));
+ REPORTER_ASSERT(r, !set.contains(SkString("Goodbye")));
+}
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