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Util: Speed up zero compression

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As suggested by orignal
This commit is contained in:
zzz
2020-05-19 14:24:20 +00:00
parent 093c46c937
commit ef66457181
3 changed files with 48 additions and 2 deletions
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39
core/java/src/net/i2p/data/DataHelper.java
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@ -42,6 +42,7 @@ import java.util.Properties;
import java.util.TimeZone;
import java.util.concurrent.ConcurrentHashMap;
import java.util.regex.Pattern;
import java.util.zip.CRC32;
import java.util.zip.Deflater;
import net.i2p.I2PAppContext;
@ -1760,6 +1761,8 @@ public class DataHelper {
*/
public static byte[] compress(byte orig[], int offset, int size, int level) {
if (orig == null) return orig;
if (level == NO_COMPRESSION && size <= 32767)
return zeroCompress(orig, offset, size);
if (size > MAX_UNCOMPRESSED)
throw new IllegalArgumentException("tell jrandom size=" + size);
ReusableGZIPOutputStream out = ReusableGZIPOutputStream.acquire();
@ -1794,7 +1797,41 @@ public class DataHelper {
}
}
/**
* Fast NO_COMPRESSION.
* 135x faster for 23 bytes, 15x faster for 1752 bytes.
*
* Ref: RFC 1951, RFC 1952, ResettableGzipOutputStream
*
* @param len 32767 max
* @return 23 bytes longer
* @since 0.9.46
*/
private static byte[] zeroCompress(byte[] in, int off, int len) {
if (len > 32767)
throw new IllegalArgumentException();
byte[] rv = new byte[len + 23];
rv[0] = 0x1F;
rv[1] = (byte) 0x8B;
rv[2] = 0x08;
rv[8] = 0x02; // XFL max compression slowest algorithm
rv[9] = (byte) 0xFF; // unknown OS
rv[10] = 0x01; // BFINAL, BTYPE = 0 (no compression)
rv[11] = (byte) (len & 0xff);
rv[12] = (byte) ((len >> 8) & 0xff);
rv[13] = (byte) ~ rv[11];
rv[14] = (byte) ~ rv[12];
System.arraycopy(in, off, rv, 15, len);
CRC32 crc = new CRC32();
crc.update(in, off, len);
long val = crc.getValue();
toLongLE(rv, rv.length - 8, 4, val);
rv[rv.length - 4] = rv[11];
rv[rv.length - 3] = rv[12];
return rv;
}
/**
* Decompress the GZIP compressed data (returning null on error).
* @throws IOException if uncompressed is over 40 KB,