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/*
 * Copyright (C) 2011 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.facebook.presto.jdbc.internal.guava.hash;

import com.facebook.presto.jdbc.internal.guava.annotations.Beta;
import com.google.errorprone.annotations.CanIgnoreReturnValue;
import java.nio.ByteBuffer;
import java.nio.charset.Charset;

/**
 * A {@link PrimitiveSink} that can compute a hash code after reading the input. Each hasher should
 * translate all multibyte values ({@link #putInt(int)}, {@link #putLong(long)}, etc) to bytes in
 * little-endian order.
 *
 * 

Warning: The result of calling any methods after calling {@link #hash} is undefined. * *

Warning: Using a specific character encoding when hashing a {@link CharSequence} with * {@link #putString(CharSequence, Charset)} is generally only useful for cross-language * compatibility (otherwise prefer {@link #putUnencodedChars}). However, the character encodings * must be identical across languages. Also beware that {@link Charset} definitions may occasionally * change between Java releases. * *

Warning: Chunks of data that are put into the {@link Hasher} are not delimited. The * resulting {@link HashCode} is dependent only on the bytes inserted, and the order in which they * were inserted, not how those bytes were chunked into discrete put() operations. For example, the * following three expressions all generate colliding hash codes: * *

{@code
 * newHasher().putByte(b1).putByte(b2).putByte(b3).hash()
 * newHasher().putByte(b1).putBytes(new byte[] { b2, b3 }).hash()
 * newHasher().putBytes(new byte[] { b1, b2, b3 }).hash()
 * }
* *

If you wish to avoid this, you should either prepend or append the size of each chunk. Keep in * mind that when dealing with char sequences, the encoded form of two concatenated char sequences * is not equivalent to the concatenation of their encoded form. Therefore, {@link * #putString(CharSequence, Charset)} should only be used consistently with complete * sequences and not broken into chunks. * * @author Kevin Bourrillion * @since 11.0 */ @Beta @CanIgnoreReturnValue public interface Hasher extends PrimitiveSink { @Override Hasher putByte(byte b); @Override Hasher putBytes(byte[] bytes); @Override Hasher putBytes(byte[] bytes, int off, int len); @Override Hasher putBytes(ByteBuffer bytes); @Override Hasher putShort(short s); @Override Hasher putInt(int i); @Override Hasher putLong(long l); /** Equivalent to {@code putInt(Float.floatToRawIntBits(f))}. */ @Override Hasher putFloat(float f); /** Equivalent to {@code putLong(Double.doubleToRawLongBits(d))}. */ @Override Hasher putDouble(double d); /** Equivalent to {@code putByte(b ? (byte) 1 : (byte) 0)}. */ @Override Hasher putBoolean(boolean b); @Override Hasher putChar(char c); /** * Equivalent to processing each {@code char} value in the {@code CharSequence}, in order. In * other words, no character encoding is performed; the low byte and high byte of each {@code * char} are hashed directly (in that order). The input must not be updated while this method is * in progress. * *

Warning: This method will produce different output than most other languages do when * running the same hash function on the equivalent input. For cross-language compatibility, use * {@link #putString}, usually with a charset of UTF-8. For other use cases, use {@code * putUnencodedChars}. * * @since 15.0 (since 11.0 as putString(CharSequence)). */ @Override Hasher putUnencodedChars(CharSequence charSequence); /** * Equivalent to {@code putBytes(charSequence.toString().getBytes(charset))}. * *

Warning: This method, which reencodes the input before hashing it, is useful only for * cross-language compatibility. For other use cases, prefer {@link #putUnencodedChars}, which is * faster, produces the same output across Java releases, and hashes every {@code char} in the * input, even if some are invalid. */ @Override Hasher putString(CharSequence charSequence, Charset charset); /** A simple convenience for {@code funnel.funnel(object, this)}. */ Hasher putObject(T instance, Funnel funnel); /** * Computes a hash code based on the data that have been provided to this hasher. The result is * unspecified if this method is called more than once on the same instance. */ HashCode hash(); /** * {@inheritDoc} * * @deprecated This returns {@link Object#hashCode()}; you almost certainly mean to call {@code * hash().asInt()}. */ @Override @Deprecated int hashCode(); }





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