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Separate ValueCompression from GorillaCompressor and allow the usage of
different value predictors. Include DFCM as another predictor possibility. (cherry picked from commit 6d0d61a)
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37 changes: 37 additions & 0 deletions
37
src/main/java/fi/iki/yak/ts/compression/gorilla/Predictor.java
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,37 @@ | ||
| /* | ||
| * Copyright 2017 Red Hat, Inc. and/or its affiliates | ||
| * and other contributors as indicated by the @author tags. | ||
| * | ||
| * 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 fi.iki.yak.ts.compression.gorilla; | ||
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| /** | ||
| * @author miburman | ||
| */ | ||
| public interface Predictor { | ||
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| /** | ||
| * Give the real value | ||
| * | ||
| * @param value Long / bits of Double | ||
| */ | ||
| void update(long value); | ||
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| /** | ||
| * Predicts the next value | ||
| * | ||
| * @return Predicted value | ||
| */ | ||
| long predict(); | ||
| } |
92 changes: 92 additions & 0 deletions
92
src/main/java/fi/iki/yak/ts/compression/gorilla/ValueCompressor.java
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,92 @@ | ||
| package fi.iki.yak.ts.compression.gorilla; | ||
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| import fi.iki.yak.ts.compression.gorilla.predictors.LastValuePredictor; | ||
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| /** | ||
| * ValueCompressor for the Gorilla encoding format. Supply with long presentation of the value, | ||
| * in case of doubles use Double.doubleToRawLongBits(value) | ||
| * | ||
| * @author Michael Burman | ||
| */ | ||
| public class ValueCompressor { | ||
| private int storedLeadingZeros = Integer.MAX_VALUE; | ||
| private int storedTrailingZeros = 0; | ||
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| private Predictor predictor; | ||
| private BitOutput out; | ||
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| public ValueCompressor(BitOutput out) { | ||
| this(out, new LastValuePredictor()); | ||
| } | ||
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| public ValueCompressor(BitOutput out, Predictor predictor) { | ||
| this.out = out; | ||
| this.predictor = predictor; | ||
| } | ||
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| void writeFirst(long value) { | ||
| predictor.update(value); | ||
| out.writeBits(value, 64); | ||
| } | ||
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| protected void compressValue(long value) { | ||
| // In original Gorilla, Last-Value predictor is used | ||
| long diff = predictor.predict() ^ value; | ||
| predictor.update(value); | ||
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| if(diff == 0) { | ||
| // Write 0 | ||
| out.skipBit(); | ||
| } else { | ||
| int leadingZeros = Long.numberOfLeadingZeros(diff); | ||
| int trailingZeros = Long.numberOfTrailingZeros(diff); | ||
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| out.writeBit(); // Optimize to writeNewLeading / writeExistingLeading? | ||
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| if(leadingZeros >= storedLeadingZeros && trailingZeros >= storedTrailingZeros) { | ||
| writeExistingLeading(diff); | ||
| } else { | ||
| writeNewLeading(diff, leadingZeros, trailingZeros); | ||
| } | ||
| } | ||
| } | ||
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| /** | ||
| * If there at least as many leading zeros and as many trailing zeros as previous value, control bit = 0 (type a) | ||
| * store the meaningful XORed value | ||
| * | ||
| * @param xor XOR between previous value and current | ||
| */ | ||
| private void writeExistingLeading(long xor) { | ||
| out.skipBit(); | ||
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| int significantBits = 64 - storedLeadingZeros - storedTrailingZeros; | ||
| xor >>>= storedTrailingZeros; | ||
| out.writeBits(xor, significantBits); | ||
| } | ||
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| /** | ||
| * store the length of the number of leading zeros in the next 5 bits | ||
| * store length of the meaningful XORed value in the next 6 bits, | ||
| * store the meaningful bits of the XORed value | ||
| * (type b) | ||
| * | ||
| * @param xor XOR between previous value and current | ||
| * @param leadingZeros New leading zeros | ||
| * @param trailingZeros New trailing zeros | ||
| */ | ||
| private void writeNewLeading(long xor, int leadingZeros, int trailingZeros) { | ||
| out.writeBit(); | ||
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| // Different from version 1.x, use (significantBits - 1) in storage - avoids a branch | ||
| int significantBits = 64 - leadingZeros - trailingZeros; | ||
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| // Different from original, bits 5 -> 6, avoids a branch, allows storing small longs | ||
| out.writeBits(leadingZeros, 6); // Number of leading zeros in the next 6 bits | ||
| out.writeBits(significantBits - 1, 6); // Length of meaningful bits in the next 6 bits | ||
| out.writeBits(xor >>> trailingZeros, significantBits); // Store the meaningful bits of XOR | ||
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| storedLeadingZeros = leadingZeros; | ||
| storedTrailingZeros = trailingZeros; | ||
| } | ||
| } |
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