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Tuple: add PreambleUtil documenting the serialized forms #784
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src/main/java/org/apache/datasketches/tuple/PreambleUtil.java
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| /* | ||
| * Licensed to the Apache Software Foundation (ASF) under one | ||
| * or more contributor license agreements. See the NOTICE file | ||
| * distributed with this work for additional information | ||
| * regarding copyright ownership. The ASF licenses this file | ||
| * to you 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. | ||
| */ | ||
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| package org.apache.datasketches.tuple; | ||
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| //@formatter:off | ||
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| /** | ||
| * This class documents the serialized forms of the generic tuple sketches, | ||
| * {@link CompactTupleSketch} and the updatable {@link QuickSelectSketch}, in one place. | ||
| * The ArrayOfDoubles sketches in the <i>arrayofdoubles</i> sub-package have their own layouts, | ||
| * which are documented in those classes. | ||
| * | ||
| * <p>MAP: Low significance bytes of this <i>long</i> data structure are on the right. | ||
| * All multi-byte values (<i>short</i>, <i>int</i>, <i>long</i>, <i>float</i> and <i>double</i>) | ||
| * are stored little-endian. The <i>byte</i> values are treated as unsigned.</p> | ||
| * | ||
| * <p>Unlike the theta sketches, a tuple sketch image is not a fixed-size table of longs. | ||
| * Each retained entry is a hash (8 bytes) followed by the bytes of its Summary, and a Summary | ||
| * may have any length. The Summary bytes are written by {@link Summary#toByteArray()} and read by a | ||
| * {@link SummaryDeserializer}, both supplied by the user. The sketch image does not record the | ||
| * Summary type. A reader must therefore know which Summary was used to write the image.</p> | ||
| * | ||
| * <h2>CompactTupleSketch, serial version 3 (current)</h2> | ||
| * | ||
| * <p>This form is binary compatible with the C++ and Go compact tuple sketches, as long as | ||
| * every language uses the same Summary encoding.</p> | ||
| * | ||
| * <p>Flags: ReadOnly, Compact, Empty if empty. The Ordered flag is defined but Java does not set it. | ||
| * The seed hash is zero when the sketch is empty, as in theta.</p> | ||
| * | ||
| * <p>An empty sketch, or a single-item sketch that is not in estimation mode, uses 1 preamble long. | ||
| * The single entry, if any, starts at byte 8.</p> | ||
| * | ||
| * <pre> | ||
| * Long || Start Byte Adr: | ||
| * Adr: | ||
| * || 7 | 6 | 5 | 4 | 3 | 2 | 1 | 0 | | ||
| * 0 || Seed Hash | Flags | unused | SkType | FamID | SerVer | PreLongs = 1 | | ||
| * | ||
| * || 15 | 14 | 13 | 12 | 11 | 10 | 9 | 8 | | ||
| * 1 ||-------------------------Hash of the single entry (if not empty)-------------------| | ||
| * | ||
| * || | | | | | | | 16 | | ||
| * 2 ||-------------------------Summary of the single entry-------------------------------| | ||
| * </pre> | ||
| * | ||
| * <p>An exact (not estimating) sketch with more than one entry uses 2 preamble longs.</p> | ||
| * | ||
| * <pre> | ||
| * Long || Start Byte Adr: | ||
| * Adr: | ||
| * || 7 | 6 | 5 | 4 | 3 | 2 | 1 | 0 | | ||
| * 0 || Seed Hash | Flags | unused | SkType | FamID | SerVer | PreLongs = 2 | | ||
| * | ||
| * || 15 | 14 | 13 | 12 | 11 | 10 | 9 | 8 | | ||
| * 1 ||-------------unused----------------|----------Retained Entries Count---------------| | ||
| * | ||
| * || 23 | 22 | 21 | 20 | 19 | 18 | 17 | 16 | | ||
| * 2 ||-------------Entries: hash (8 bytes), then Summary bytes, repeated Count times-----| | ||
| * </pre> | ||
| * | ||
| * <p>An estimating sketch uses 3 preamble longs.</p> | ||
| * | ||
| * <pre> | ||
| * Long || Start Byte Adr: | ||
| * Adr: | ||
| * || 7 | 6 | 5 | 4 | 3 | 2 | 1 | 0 | | ||
| * 0 || Seed Hash | Flags | unused | SkType | FamID | SerVer | PreLongs = 3 | | ||
| * | ||
| * || 15 | 14 | 13 | 12 | 11 | 10 | 9 | 8 | | ||
| * 1 ||-------------unused----------------|----------Retained Entries Count---------------| | ||
| * | ||
| * || 23 | 22 | 21 | 20 | 19 | 18 | 17 | 16 | | ||
| * 2 ||------------------------------THETA_LONG-------------------------------------------| | ||
| * | ||
| * || 31 | 30 | 29 | 28 | 27 | 26 | 25 | 24 | | ||
| * 3 ||-------------Entries: hash (8 bytes), then Summary bytes, repeated Count times-----| | ||
| * </pre> | ||
| * | ||
| * <h2>CompactTupleSketch, serial versions 1 and 2 (legacy, read only)</h2> | ||
| * | ||
| * <p>Java no longer writes these forms but can still read them. The fields after byte 4 are | ||
| * packed with no alignment, and each one is present only if its flag is set.</p> | ||
| * | ||
| * <pre> | ||
| * Byte Adr | Size | Field | ||
| * 0 | 1 | PreLongs | ||
| * 1 | 1 | SerVer = 1 or 2 | ||
| * 2 | 1 | FamID | ||
| * 3 | 1 | SkType = CompactTupleSketch | ||
| * 4 | 1 | Flags (legacy bits, see below) | ||
| * 5 | 8 | THETA_LONG, if IS_THETA_INCLUDED | ||
| * next | 1 | Summary class-name length N, if HAS_ENTRIES and SerVer = 1 | ||
| * next | 4 | Retained Entries Count, if HAS_ENTRIES | ||
| * next | N | Summary class name, if HAS_ENTRIES and SerVer = 1 (skipped) | ||
| * next | 8*C | Count hashes, if HAS_ENTRIES | ||
| * next | var | Count Summaries, if HAS_ENTRIES | ||
| * </pre> | ||
| * | ||
| * <h2>QuickSelectSketch (updatable), serial version 2 (deprecated)</h2> | ||
| * | ||
| * <p>Serializing an updatable sketch is deprecated. This form has no seed hash and is | ||
| * read only by Java. As with the legacy compact form, the fields after byte 7 are | ||
| * packed, and each one is present only if its flag is set.</p> | ||
| * | ||
| * <pre> | ||
| * Long || Start Byte Adr: | ||
| * Adr: | ||
| * || 7 | 6 | 5 | 4 | 3 | 2 | 1 | 0 | | ||
| * 0 || LgRF | LgArr | LgNom | Flags | SkType | FamID | SerVer | PreLongs = 1 | | ||
| * | ||
| * Byte Adr | Size | Field | ||
| * 8 | 4 | Sampling probability p (float), if IS_IN_SAMPLING_MODE | ||
| * next | 8 | THETA_LONG, if IS_THETA_INCLUDED | ||
| * next | 4 | Retained Entries Count, if HAS_ENTRIES | ||
| * next | var | Entries: hash (8 bytes), then Summary bytes, repeated Count times | ||
| * </pre> | ||
| * | ||
| * <h2>Flags byte</h2> | ||
| * | ||
| * <pre> | ||
| * Bit | CompactTupleSketch v3 | CompactTupleSketch v1, v2 | QuickSelectSketch v2 | ||
| * 0 | Reserved | IS_BIG_ENDIAN (unused) | Reserved | ||
| * 1 | IS_READ_ONLY | IS_EMPTY | IS_IN_SAMPLING_MODE | ||
| * 2 | IS_EMPTY | HAS_ENTRIES | IS_EMPTY | ||
| * 3 | IS_COMPACT | IS_THETA_INCLUDED | HAS_ENTRIES | ||
| * 4 | IS_ORDERED | | IS_THETA_INCLUDED | ||
| * </pre> | ||
| * | ||
| * <h2>Summary encodings of the example Summaries in this library</h2> | ||
| * | ||
| * <p>The Summaries in the <i>adouble</i>, <i>aninteger</i> and <i>strings</i> sub-packages are | ||
| * examples of user-defined Summaries. Their encodings are specific to Java, and other languages | ||
| * can read them only through custom code. The Mode byte is the ordinal of the Summary's Mode: | ||
| * Sum = 0, Min = 1, Max = 2, AlwaysOne = 3.</p> | ||
| * | ||
| * <pre> | ||
| * Summary | Bytes | Encoding | ||
| * DoubleSummary | 9 | double value (bytes 0-7), Mode (byte 8) | ||
| * IntegerSummary | 5 | int value (bytes 0-3), Mode (byte 4) | ||
| * ArrayOfStringsSummary | var | int total bytes, byte number of strings, | ||
| * | | then for each string: int length, then its UTF-8 bytes | ||
| * </pre> | ||
| * | ||
| * @author Lee Rhodes | ||
| */ | ||
| final class PreambleUtil { | ||
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| private PreambleUtil() {} | ||
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| // Byte addresses common to all forms | ||
| static final int PREAMBLE_LONGS_BYTE = 0; | ||
| static final int SER_VER_BYTE = 1; | ||
| static final int FAMILY_BYTE = 2; | ||
| static final int SKETCH_TYPE_BYTE = 3; | ||
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| // CompactTupleSketch, serial version 3 | ||
| static final int COMPACT_FLAGS_BYTE = 5; | ||
| static final int SEED_HASH_SHORT = 6; //bytes 6,7 | ||
| static final int RETAINED_ENTRIES_INT = 8; //only if PreLongs > 1 | ||
| static final int THETA_LONG = 16; //only if PreLongs = 3 | ||
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| // CompactTupleSketch, serial versions 1 and 2, and QuickSelectSketch | ||
| static final int LEGACY_FLAGS_BYTE = 4; | ||
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| // QuickSelectSketch, serial version 2 | ||
| static final int LG_NOM_ENTRIES_BYTE = 5; | ||
| static final int LG_CUR_CAPACITY_BYTE = 6; | ||
| static final int LG_RESIZE_FACTOR_BYTE = 7; | ||
| static final int QS_VARIABLE_START = 8; | ||
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| // Serial versions | ||
| static final byte COMPACT_SER_VER_WITH_CLASS_NAME = 1; | ||
| static final byte COMPACT_SER_VER_LEGACY = 2; | ||
| static final byte COMPACT_SER_VER = 3; | ||
| static final byte QUICK_SELECT_SER_VER = 2; | ||
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| } | ||
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