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The official Couchbase JVM Core IO Library
/*
* Copyright (C) 2011 the original author or authors.
* See the notice.md file distributed with this work for additional
* information regarding copyright ownership.
*
* 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.couchbase.client.core.deps.org.iq80.snappy;
import static com.couchbase.client.core.deps.org.iq80.snappy.SnappyInternalUtils.copyLong;
import static com.couchbase.client.core.deps.org.iq80.snappy.SnappyInternalUtils.loadByte;
import static com.couchbase.client.core.deps.org.iq80.snappy.SnappyInternalUtils.lookupShort;
final class SnappyDecompressor
{
private static final int MAX_INCREMENT_COPY_OVERFLOW = 20;
public static int getUncompressedLength(byte[] compressed, int compressedOffset)
throws CorruptionException
{
return readUncompressedLength(compressed, compressedOffset)[0];
}
public static byte[] uncompress(byte[] compressed, int compressedOffset, int compressedSize)
throws CorruptionException
{
// Read the uncompressed length from the front of the compressed input
int[] varInt = readUncompressedLength(compressed, compressedOffset);
int expectedLength = varInt[0];
compressedOffset += varInt[1];
compressedSize -= varInt[1];
// allocate the uncompressed buffer
byte[] uncompressed = new byte[expectedLength];
// Process the entire input
int uncompressedSize = decompressAllTags(
compressed,
compressedOffset,
compressedSize,
uncompressed,
0);
if (!(expectedLength == uncompressedSize)) {
throw new CorruptionException(String.format("Recorded length is %s bytes but actual length after decompression is %s bytes ",
expectedLength,
uncompressedSize));
}
return uncompressed;
}
public static int uncompress(byte[] compressed, int compressedOffset, int compressedSize, byte[] uncompressed, int uncompressedOffset)
throws CorruptionException
{
// Read the uncompressed length from the front of the compressed input
int[] varInt = readUncompressedLength(compressed, compressedOffset);
int expectedLength = varInt[0];
compressedOffset += varInt[1];
compressedSize -= varInt[1];
SnappyInternalUtils.checkArgument(expectedLength <= uncompressed.length - uncompressedOffset,
"Uncompressed length %s must be less than %s", expectedLength, uncompressed.length - uncompressedOffset);
// Process the entire input
int uncompressedSize = decompressAllTags(
compressed,
compressedOffset,
compressedSize,
uncompressed,
uncompressedOffset);
if (!(expectedLength == uncompressedSize)) {
throw new CorruptionException(String.format("Recorded length is %s bytes but actual length after decompression is %s bytes ",
expectedLength,
uncompressedSize));
}
return expectedLength;
}
private static int decompressAllTags(
final byte[] input,
final int inputOffset,
final int inputSize,
final byte[] output,
final int outputOffset)
throws CorruptionException
{
final int outputLimit = output.length;
final int ipLimit = inputOffset + inputSize;
int opIndex = outputOffset;
int ipIndex = inputOffset;
while (ipIndex < ipLimit - 5) {
int opCode = loadByte(input, ipIndex++);
int entry = lookupShort(opLookupTable, opCode);
int trailerBytes = entry >>> 11;
int trailer = readTrailer(input, ipIndex, trailerBytes);
// advance the ipIndex past the op codes
ipIndex += entry >>> 11;
int length = entry & 0xff;
if ((opCode & 0x3) == Snappy.LITERAL) {
int literalLength = length + trailer;
copyLiteral(input, ipIndex, output, opIndex, literalLength);
ipIndex += literalLength;
opIndex += literalLength;
}
else {
// copyOffset/256 is encoded in bits 8..10. By just fetching
// those bits, we get copyOffset (since the bit-field starts at
// bit 8).
int copyOffset = entry & 0x700;
copyOffset += trailer;
// inline to force hot-spot to keep inline
//
// Equivalent to incrementalCopy (below) except that it can write up to ten extra
// bytes after the end of the copy, and that it is faster.
//
// The main part of this loop is a simple copy of eight bytes at a time until
// we've copied (at least) the requested amount of bytes. However, if op and
// src are less than eight bytes apart (indicating a repeating pattern of
// length < 8), we first need to expand the pattern in order to get the correct
// results. For instance, if the buffer looks like this, with the eight-byte
// and patterns marked as intervals:
//
// abxxxxxxxxxxxx
// [------] src
// [------] op
//
// a single eight-byte copy from to will repeat the pattern once,
// after which we can move two bytes without moving :
//
// ababxxxxxxxxxx
// [------] src
// [------] op
//
// and repeat the exercise until the two no longer overlap.
//
// This allows us to do very well in the special case of one single byte
// repeated many times, without taking a big hit for more general cases.
//
// The worst case of extra writing past the end of the match occurs when
// op - src == 1 and len == 1; the last copy will read from byte positions
// [0..7] and write to [4..11], whereas it was only supposed to write to
// position 1. Thus, ten excess bytes.
{
int spaceLeft = outputLimit - opIndex;
int srcIndex = opIndex - copyOffset;
if (srcIndex < outputOffset) {
throw new CorruptionException("Invalid copy offset for opcode starting at " + (ipIndex - trailerBytes - 1));
}
if (length <= 16 && copyOffset >= 8 && spaceLeft >= 16) {
// Fast path, used for the majority (70-80%) of dynamic invocations.
copyLong(output, srcIndex, output, opIndex);
copyLong(output, srcIndex + 8, output, opIndex + 8);
}
else if (spaceLeft >= length + MAX_INCREMENT_COPY_OVERFLOW) {
incrementalCopyFastPath(output, srcIndex, opIndex, length);
}
else {
incrementalCopy(output, srcIndex, output, opIndex, length);
}
}
opIndex += length;
}
}
for (; ipIndex < ipLimit; ) {
int[] result = decompressTagSlow(input, ipIndex, output, outputLimit, outputOffset, opIndex);
ipIndex = result[0];
opIndex = result[1];
}
return opIndex - outputOffset;
}
/**
* This is a second copy of the inner loop of decompressTags used when near the end
* of the input. The key difference is the reading of the trailer bytes. The fast
* code does a blind read of the next 4 bytes as an int, and this code assembles
* the int byte-by-byte to assure that the array is not over run. The reason this
* code path is separate is the if condition to choose between these two seemingly
* small differences costs like 10-20% of the throughput. I'm hoping in future
* versions of hot-spot this code can be integrated into the main loop but for now
* it is worth the extra maintenance pain to get the extra 10-20%.
*/
private static int[] decompressTagSlow(byte[] input, int ipIndex, byte[] output, int outputLimit, int outputOffset, int opIndex)
throws CorruptionException
{
// read the op code
int opCode = loadByte(input, ipIndex++);
int entry = lookupShort(opLookupTable, opCode);
int trailerBytes = entry >>> 11;
//
// Key difference here
//
int trailer = 0;
switch (trailerBytes) {
case 4:
trailer = (input[ipIndex + 3] & 0xff) << 24;
case 3:
trailer |= (input[ipIndex + 2] & 0xff) << 16;
case 2:
trailer |= (input[ipIndex + 1] & 0xff) << 8;
case 1:
trailer |= (input[ipIndex] & 0xff);
}
// advance the ipIndex past the op codes
ipIndex += trailerBytes;
int length = entry & 0xff;
if ((opCode & 0x3) == Snappy.LITERAL) {
int literalLength = length + trailer;
copyLiteral(input, ipIndex, output, opIndex, literalLength);
ipIndex += literalLength;
opIndex += literalLength;
}
else {
// copyOffset/256 is encoded in bits 8..10. By just fetching
// those bits, we get copyOffset (since the bit-field starts at
// bit 8).
int copyOffset = entry & 0x700;
copyOffset += trailer;
// inline to force hot-spot to keep inline
{
int spaceLeft = outputLimit - opIndex;
int srcIndex = opIndex - copyOffset;
if (srcIndex < outputOffset) {
throw new CorruptionException("Invalid copy offset for opcode starting at " + (ipIndex - trailerBytes - 1));
}
if (length <= 16 && copyOffset >= 8 && spaceLeft >= 16) {
// Fast path, used for the majority (70-80%) of dynamic invocations.
copyLong(output, srcIndex, output, opIndex);
copyLong(output, srcIndex + 8, output, opIndex + 8);
}
else if (spaceLeft >= length + MAX_INCREMENT_COPY_OVERFLOW) {
incrementalCopyFastPath(output, srcIndex, opIndex, length);
}
else {
incrementalCopy(output, srcIndex, output, opIndex, length);
}
}
opIndex += length;
}
return new int[] {ipIndex, opIndex};
}
private static int readTrailer(byte[] data, int index, int bytes)
{
return SnappyInternalUtils.loadInt(data, index) & wordmask[bytes];
}
private static void copyLiteral(byte[] input, int ipIndex, byte[] output, int opIndex, int length)
throws CorruptionException
{
assert length > 0;
assert ipIndex >= 0;
assert opIndex >= 0;
int spaceLeft = output.length - opIndex;
int readableBytes = input.length - ipIndex;
if (readableBytes < length || spaceLeft < length) {
throw new CorruptionException("Corrupt literal length");
}
if (length <= 16 && spaceLeft >= 16 && readableBytes >= 16) {
copyLong(input, ipIndex, output, opIndex);
copyLong(input, ipIndex + 8, output, opIndex + 8);
}
else {
int fastLength = length & 0xFFFFFFF8;
if (fastLength <= 64) {
// copy long-by-long
for (int i = 0; i < fastLength; i += 8) {
copyLong(input, ipIndex + i, output, opIndex + i);
}
// copy byte-by-byte
int slowLength = length & 0x7;
// NOTE: This is not a manual array copy. We are copying an overlapping region
// and we want input data to repeat as it is recopied. see incrementalCopy below.
//noinspection ManualArrayCopy
for (int i = 0; i < slowLength; i += 1) {
output[opIndex + fastLength + i] = input[ipIndex + fastLength + i];
}
}
else {
SnappyInternalUtils.copyMemory(input, ipIndex, output, opIndex, length);
}
}
}
/**
* Copy "len" bytes from "src" to "op", one byte at a time. Used for
* handling COPY operations where the input and output regions may
* overlap. For example, suppose:
* src == "ab"
* op == src + 2
* len == 20
*
* After incrementalCopy, the result will have
* eleven copies of "ab"
* ababababababababababab
* Note that this does not match the semantics of either memcpy()
* or memmove().
*/
private static void incrementalCopy(byte[] src, int srcIndex, byte[] op, int opIndex, int length)
{
do {
op[opIndex++] = src[srcIndex++];
} while (--length > 0);
}
private static void incrementalCopyFastPath(byte[] output, int srcIndex, int opIndex, int length)
{
int copiedLength = 0;
while ((opIndex + copiedLength) - srcIndex < 8) {
copyLong(output, srcIndex, output, opIndex + copiedLength);
copiedLength += (opIndex + copiedLength) - srcIndex;
}
for (int i = 0; i < length - copiedLength; i += 8) {
copyLong(output, srcIndex + i, output, opIndex + copiedLength + i);
}
}
// Mapping from i in range [0,4] to a mask to extract the bottom 8*i bits
private static final int[] wordmask = new int[] {
0, 0xff, 0xffff, 0xffffff, 0xffffffff
};
// Data stored per entry in lookup table:
// Range Bits-used Description
// ------------------------------------
// 1..64 0..7 Literal/copy length encoded in opcode byte
// 0..7 8..10 Copy offset encoded in opcode byte / 256
// 0..4 11..13 Extra bytes after opcode
//
// We use eight bits for the length even though 7 would have sufficed
// because of efficiency reasons:
// (1) Extracting a byte is faster than a bit-field
// (2) It properly aligns copy offset so we do not need a <<8
private static final short[] opLookupTable = new short[] {
0x0001, 0x0804, 0x1001, 0x2001, 0x0002, 0x0805, 0x1002, 0x2002,
0x0003, 0x0806, 0x1003, 0x2003, 0x0004, 0x0807, 0x1004, 0x2004,
0x0005, 0x0808, 0x1005, 0x2005, 0x0006, 0x0809, 0x1006, 0x2006,
0x0007, 0x080a, 0x1007, 0x2007, 0x0008, 0x080b, 0x1008, 0x2008,
0x0009, 0x0904, 0x1009, 0x2009, 0x000a, 0x0905, 0x100a, 0x200a,
0x000b, 0x0906, 0x100b, 0x200b, 0x000c, 0x0907, 0x100c, 0x200c,
0x000d, 0x0908, 0x100d, 0x200d, 0x000e, 0x0909, 0x100e, 0x200e,
0x000f, 0x090a, 0x100f, 0x200f, 0x0010, 0x090b, 0x1010, 0x2010,
0x0011, 0x0a04, 0x1011, 0x2011, 0x0012, 0x0a05, 0x1012, 0x2012,
0x0013, 0x0a06, 0x1013, 0x2013, 0x0014, 0x0a07, 0x1014, 0x2014,
0x0015, 0x0a08, 0x1015, 0x2015, 0x0016, 0x0a09, 0x1016, 0x2016,
0x0017, 0x0a0a, 0x1017, 0x2017, 0x0018, 0x0a0b, 0x1018, 0x2018,
0x0019, 0x0b04, 0x1019, 0x2019, 0x001a, 0x0b05, 0x101a, 0x201a,
0x001b, 0x0b06, 0x101b, 0x201b, 0x001c, 0x0b07, 0x101c, 0x201c,
0x001d, 0x0b08, 0x101d, 0x201d, 0x001e, 0x0b09, 0x101e, 0x201e,
0x001f, 0x0b0a, 0x101f, 0x201f, 0x0020, 0x0b0b, 0x1020, 0x2020,
0x0021, 0x0c04, 0x1021, 0x2021, 0x0022, 0x0c05, 0x1022, 0x2022,
0x0023, 0x0c06, 0x1023, 0x2023, 0x0024, 0x0c07, 0x1024, 0x2024,
0x0025, 0x0c08, 0x1025, 0x2025, 0x0026, 0x0c09, 0x1026, 0x2026,
0x0027, 0x0c0a, 0x1027, 0x2027, 0x0028, 0x0c0b, 0x1028, 0x2028,
0x0029, 0x0d04, 0x1029, 0x2029, 0x002a, 0x0d05, 0x102a, 0x202a,
0x002b, 0x0d06, 0x102b, 0x202b, 0x002c, 0x0d07, 0x102c, 0x202c,
0x002d, 0x0d08, 0x102d, 0x202d, 0x002e, 0x0d09, 0x102e, 0x202e,
0x002f, 0x0d0a, 0x102f, 0x202f, 0x0030, 0x0d0b, 0x1030, 0x2030,
0x0031, 0x0e04, 0x1031, 0x2031, 0x0032, 0x0e05, 0x1032, 0x2032,
0x0033, 0x0e06, 0x1033, 0x2033, 0x0034, 0x0e07, 0x1034, 0x2034,
0x0035, 0x0e08, 0x1035, 0x2035, 0x0036, 0x0e09, 0x1036, 0x2036,
0x0037, 0x0e0a, 0x1037, 0x2037, 0x0038, 0x0e0b, 0x1038, 0x2038,
0x0039, 0x0f04, 0x1039, 0x2039, 0x003a, 0x0f05, 0x103a, 0x203a,
0x003b, 0x0f06, 0x103b, 0x203b, 0x003c, 0x0f07, 0x103c, 0x203c,
0x0801, 0x0f08, 0x103d, 0x203d, 0x1001, 0x0f09, 0x103e, 0x203e,
0x1801, 0x0f0a, 0x103f, 0x203f, 0x2001, 0x0f0b, 0x1040, 0x2040
};
/**
* Reads the variable length integer encoded a the specified offset, and
* returns this length with the number of bytes read.
*/
private static int[] readUncompressedLength(byte[] compressed, int compressedOffset)
throws CorruptionException
{
int result;
int bytesRead = 0;
{
int b = compressed[compressedOffset + bytesRead++] & 0xFF;
result = b & 0x7f;
if ((b & 0x80) != 0) {
b = compressed[compressedOffset + bytesRead++] & 0xFF;
result |= (b & 0x7f) << 7;
if ((b & 0x80) != 0) {
b = compressed[compressedOffset + bytesRead++] & 0xFF;
result |= (b & 0x7f) << 14;
if ((b & 0x80) != 0) {
b = compressed[compressedOffset + bytesRead++] & 0xFF;
result |= (b & 0x7f) << 21;
if ((b & 0x80) != 0) {
b = compressed[compressedOffset + bytesRead++] & 0xFF;
result |= (b & 0x7f) << 28;
if ((b & 0x80) != 0) {
throw new CorruptionException("last byte of compressed length int has high bit set");
}
}
}
}
}
}
return new int[] {result, bytesRead};
}
}