Use Java's hardware-accelerated CRC32C implementation where available.

android/guava-tests/benchmark/com/google/common/hash/ChecksumBenchmark.java

@@ -69,6 +69,13 @@ byte crc32Checksum(int reps) throws Exception {
     return result;
   }
 
+  // CRC32C
+
+  @Benchmark
+  byte crc32cHashFunction(int reps) {
+    return runHashFunction(reps, Hashing.crc32c());
+  }
+
   // Adler32
 
   @Benchmark

android/guava/src/com/google/common/hash/IgnoreJRERequirement.java

@@ -0,0 +1,30 @@
+/*
+ * Copyright 2019 The Guava Authors
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except
+ * in compliance with the License. You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software distributed under the License
+ * is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express
+ * or implied. See the License for the specific language governing permissions and limitations under
+ * the License.
+ */
+
+package com.google.common.hash;
+
+import static java.lang.annotation.ElementType.CONSTRUCTOR;
+import static java.lang.annotation.ElementType.METHOD;
+import static java.lang.annotation.ElementType.TYPE;
+
+import java.lang.annotation.Target;
+
+/**
+ * Disables Animal Sniffer's checking of compatibility with older versions of Java/Android.
+ *
+ * <p>Each package's copy of this annotation needs to be listed in our {@code pom.xml}.
+ */
+@Target({METHOD, CONSTRUCTOR, TYPE})
+@ElementTypesAreNonnullByDefault
+@interface IgnoreJRERequirement {}

android/pom.xml

@@ -176,7 +176,7 @@
           <artifactId>animal-sniffer-maven-plugin</artifactId>
           <version>1.23</version>
           <configuration>
-            <annotations>com.google.common.io.IgnoreJRERequirement,com.google.common.reflect.IgnoreJRERequirement,com.google.common.testing.IgnoreJRERequirement</annotations>
+            <annotations>com.google.common.hash.IgnoreJRERequirement,com.google.common.io.IgnoreJRERequirement,com.google.common.reflect.IgnoreJRERequirement,com.google.common.testing.IgnoreJRERequirement</annotations>
             <checkTestClasses>true</checkTestClasses>
             <signature>
               <groupId>org.codehaus.mojo.signature</groupId>

guava-tests/benchmark/com/google/common/hash/ChecksumBenchmark.java

@@ -69,6 +69,13 @@ byte crc32Checksum(int reps) throws Exception {
     return result;
   }
 
+  // CRC32C
+
+  @Benchmark
+  byte crc32cHashFunction(int reps) {
+    return runHashFunction(reps, Hashing.crc32c());
+  }
+
   // Adler32
 
   @Benchmark

guava/src/com/google/common/hash/Hashing.java

@@ -16,8 +16,13 @@
 
 import static com.google.common.base.Preconditions.checkArgument;
 import static com.google.common.base.Preconditions.checkNotNull;
+import static com.google.common.base.Throwables.throwIfUnchecked;
+import static java.lang.invoke.MethodType.methodType;
 
 import com.google.errorprone.annotations.Immutable;
+import com.google.j2objc.annotations.J2ObjCIncompatible;
+import java.lang.invoke.MethodHandle;
+import java.lang.invoke.MethodHandles;
 import java.security.Key;
 import java.util.ArrayList;
 import java.util.Arrays;
@@ -399,14 +404,40 @@ public static HashFunction crc32c() {
 
   @Immutable
   private enum Crc32CSupplier implements ImmutableSupplier<HashFunction> {
+    @J2ObjCIncompatible
+    JAVA_UTIL_ZIP {
+      @Override
+      public HashFunction get() {
+        return ChecksumType.CRC_32C.hashFunction;
+      }
+    },
     ABSTRACT_HASH_FUNCTION {
       @Override
       public HashFunction get() {
         return Crc32cHashFunction.CRC_32_C;
       }
     };
 
-    static final HashFunction HASH_FUNCTION = values()[0].get();
+    static final HashFunction HASH_FUNCTION = pickFunction().get();
+
+    private static Crc32CSupplier pickFunction() {
+      Crc32CSupplier[] functions = values();
+
+      if (functions.length == 1) {
+        // We're running under J2ObjC.
+        return functions[0];
+      }
+
+      // We can't refer to JAVA_UTIL_ZIP directly at compile time because of J2ObjC.
+      Crc32CSupplier javaUtilZip = functions[0];
+
+      try {
+        Class.forName("java.util.zip.CRC32C");
+        return javaUtilZip;
+      } catch (ClassNotFoundException runningUnderJava8) {
+        return ABSTRACT_HASH_FUNCTION;
+      }
+    }
   }
 
   /**
@@ -449,6 +480,13 @@ public Checksum get() {
         return new CRC32();
       }
     },
+    @J2ObjCIncompatible
+    CRC_32C("Hashing.crc32c()") {
+      @Override
+      public Checksum get() {
+        return Crc32cMethodHandles.newCrc32c();
+      }
+    },
     ADLER_32("Hashing.adler32()") {
       @Override
       public Checksum get() {
@@ -463,6 +501,52 @@ public Checksum get() {
     }
   }
 
+  @J2ObjCIncompatible
+  @SuppressWarnings("unused")
+  private static final class Crc32cMethodHandles {
+    private static final MethodHandle CONSTRUCTOR = crc32cConstructor();
+
+    @IgnoreJRERequirement // https://github.com/mojohaus/animal-sniffer/issues/67
+    static Checksum newCrc32c() {
+      try {
+        return (Checksum) CONSTRUCTOR.invokeExact();
+      } catch (Throwable e) {
+        throwIfUnchecked(e);
+        // That constructor has no `throws` clause.
+        throw newLinkageError(e);
+      }
+    }
+
+    private static MethodHandle crc32cConstructor() {
+      try {
+        Class<?> clazz = Class.forName("java.util.zip.CRC32C");
+        /*
+         * We can't cast to CRC32C at the call site because we support building with Java 8
+         * (https://github.com/google/guava/issues/6549). So we have to use asType() to change from
+         * CRC32C to Checksum. This may carry some performance cost
+         * (https://stackoverflow.com/a/22321671/28465), but I'd have to benchmark more carefully to
+         * even detect it.
+         */
+        return MethodHandles.lookup()
+            .findConstructor(clazz, methodType(void.class))
+            .asType(methodType(Checksum.class));
+      } catch (ClassNotFoundException e) {
+        // We check that the class is available before calling this method.
+        throw new AssertionError(e);
+      } catch (IllegalAccessException e) {
+        // That API is public.
+        throw newLinkageError(e);
+      } catch (NoSuchMethodException e) {
+        // That constructor exists.
+        throw newLinkageError(e);
+      }
+    }
+
+    private static LinkageError newLinkageError(Throwable cause) {
+      return new LinkageError(cause.toString(), cause);
+    }
+  }
+
   /**
    * Returns a hash function implementing FarmHash's Fingerprint64, an open-source algorithm.
    *

guava/src/com/google/common/hash/IgnoreJRERequirement.java

@@ -0,0 +1,30 @@
+/*
+ * Copyright 2019 The Guava Authors
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except
+ * in compliance with the License. You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software distributed under the License
+ * is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express
+ * or implied. See the License for the specific language governing permissions and limitations under
+ * the License.
+ */
+
+package com.google.common.hash;
+
+import static java.lang.annotation.ElementType.CONSTRUCTOR;
+import static java.lang.annotation.ElementType.METHOD;
+import static java.lang.annotation.ElementType.TYPE;
+
+import java.lang.annotation.Target;
+
+/**
+ * Disables Animal Sniffer's checking of compatibility with older versions of Java/Android.
+ *
+ * <p>Each package's copy of this annotation needs to be listed in our {@code pom.xml}.
+ */
+@Target({METHOD, CONSTRUCTOR, TYPE})
+@ElementTypesAreNonnullByDefault
+@interface IgnoreJRERequirement {}

pom.xml

@@ -177,7 +177,7 @@
           <artifactId>animal-sniffer-maven-plugin</artifactId>
           <version>1.23</version>
           <configuration>
-            <annotations>com.google.common.io.IgnoreJRERequirement,com.google.common.reflect.IgnoreJRERequirement,com.google.common.testing.IgnoreJRERequirement</annotations>
+            <annotations>com.google.common.hash.IgnoreJRERequirement,com.google.common.io.IgnoreJRERequirement,com.google.common.reflect.IgnoreJRERequirement,com.google.common.testing.IgnoreJRERequirement</annotations>
             <checkTestClasses>true</checkTestClasses>
             <signature>
               <groupId>org.codehaus.mojo.signature</groupId>