Some usability ideas around SkTHash.

  - By default, use new SkGoodHash to hash keys, which is:
    * for 4 byte values, use SkChecksum::Mix,
    * for SkStrings, use SkChecksum::Murmur3 on the data,
    * for other structs, shallow hash the struct with Murmur3.
  - Expand SkChecksum::Murmur3 to support non-4-byte-aligned data.
  - Add const foreach() methods.
  - Have foreach() take a functor, which allows lambdas.

BUG=skia:

Review URL: https://codereview.chromium.org/1021033002

2 files changed, 24 insertions, 8 deletions

diff --git a/tests/ChecksumTest.cpp b/tests/ChecksumTest.cpp
index 6248678043..3658bd771e 100644
--- a/tests/ChecksumTest.cpp
+++ b/tests/ChecksumTest.cpp
@@ -50,3 +50,16 @@ DEF_TEST(Checksum, r) {
         }
     }
 }
+
+DEF_TEST(GoodHash, r) {
+    ASSERT(SkGoodHash(( int32_t)4) ==  614249093);  // 4 bytes.  Hits SkChecksum::Mix fast path.
+    ASSERT(SkGoodHash((uint32_t)4) ==  614249093);  // (Ditto)
+
+    // None of these are 4 byte sized, so they use SkChecksum::Murmur3, not SkChecksum::Mix.
+    ASSERT(SkGoodHash((uint64_t)4) == 3491892518);
+    ASSERT(SkGoodHash((uint16_t)4) ==  899251846);
+    ASSERT(SkGoodHash( (uint8_t)4) ==  962700458);
+
+    // Tests SkString is correctly specialized.
+    ASSERT(SkGoodHash(SkString("Hi")) == 55667557);
+}
diff --git a/tests/HashTest.cpp b/tests/HashTest.cpp
index 623e597eeb..5abf3db50a 100644
--- a/tests/HashTest.cpp
+++ b/tests/HashTest.cpp
@@ -3,12 +3,15 @@
 #include "SkTHash.h"
 #include "Test.h"
 
-namespace { uint32_t hash_int(const int& k) { return SkChecksum::Mix(k); } }
-
-static void set_negative_key(int key, double* d) { *d = -key; }
+// Tests use of const foreach().  map.count() is of course the better way to do this.
+static int count(const SkTHashMap<int, double>& map) {
+    int n = 0;
+    map.foreach([&n](int, double) { n++; });
+    return n;
+}
 
 DEF_TEST(HashMap, r) {
-    SkTHashMap<int, double, hash_int> map;
+    SkTHashMap<int, double> map;
 
     map.set(3, 4.0);
     REPORTER_ASSERT(r, map.count() == 1);
@@ -17,7 +20,9 @@ DEF_TEST(HashMap, r) {
     REPORTER_ASSERT(r, found);
     REPORTER_ASSERT(r, *found == 4.0);
 
-    map.foreach(set_negative_key);
+    map.foreach([](int key, double* d){ *d = -key; });
+    REPORTER_ASSERT(r, count(map) == 1);
+
     found = map.find(3);
     REPORTER_ASSERT(r, found);
     REPORTER_ASSERT(r, *found == -3.0);
@@ -44,10 +49,8 @@ DEF_TEST(HashMap, r) {
     REPORTER_ASSERT(r, map.count() == 0);
 }
 
-namespace { uint32_t hash_string(const SkString& s) { return SkToInt(s.size()); } }
-
 DEF_TEST(HashSet, r) {
-    SkTHashSet<SkString, hash_string> set;
+    SkTHashSet<SkString> set;
 
     set.add(SkString("Hello"));
     set.add(SkString("World"));