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// Copyright Vespa.ai. Licensed under the terms of the Apache 2.0 license. See LICENSE in the project root.
package com.yahoo.compress;
import java.nio.ByteBuffer;
/**
* Utility for bytewise compressing of integers into a ByteBuffer.
*
* @author baldersheim
*/
public class IntegerCompressor {
public enum Mode { NONE, COMPRESSED, COMPRESSED_POSITIVE; }
public static Mode compressionMode(int min, int max) {
if (min >= 0 && max < 1 << 30) return Mode.COMPRESSED_POSITIVE;
if (min > -1 << 29 && max < 1 << 29) return Mode.COMPRESSED;
return Mode.NONE;
}
public static void putCompressedNumber(int n, ByteBuffer buf) {
int negative = n < 0 ? 0x80 : 0x0;
if (negative != 0) {
n = -n;
if (n == -n) --n; // underflow, caught as "too big" later.
}
if (n < (0x1 << 5)) {
byte b = (byte)(n | negative);
buf.put(b);
} else if (n < (0x1 << 13)) {
n = n | 0x4000 | (negative << 8);
buf.putShort((short)n);
} else if ( n < (0x1 << 29)) {
n = n | 0x60000000 | (negative << 24);
buf.putInt(n);
} else {
throw new IllegalArgumentException("Number '" + ((negative != 0) ? -n : n) + "' too big, must extend encoding");
}
}
public static void putCompressedPositiveNumber(int n, ByteBuffer buf) {
if (n < 0) {
throw new IllegalArgumentException("Number '" + n + "' must be positive");
}
if (n < (0x1 << 6)) {
buf.put((byte)n);
} else if (n < (0x1 << 14)) {
n = n | 0x8000;
buf.putShort((short)n);
} else if ( n < (0x1 << 30)) {
n = n | 0xc0000000;
buf.putInt(n);
} else {
throw new IllegalArgumentException("Number '" + n + "' too big, must extend encoding");
}
}
}
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