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Simplify HpackHuffmanDecoder table decode logic (#9335)

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Motivation

The nice change made by @carl-mastrangelo in #9307 for lookup-table
based HPACK Huffman decoding can be simplified a little to remove the
separate flags field and eliminate some intermediate operations.

Modification

Simplify HpackHuffmanDecoder::decode logic including de-dup of the
per-nibble part.

Result

Less code, possibly better performance though not noticeable in a quick
benchmark.
This commit is contained in:
Nick Hill 2019-07-08 03:04:20 -07:00 committed by Norman Maurer
parent db8dd66f09
commit 91d6e0ea8f
1 changed files with 15 additions and 23 deletions
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38
codec-http2/src/main/java/io/netty/handler/codec/http2/HpackHuffmanDecoder.java
View File

@ -46,9 +46,9 @@ final class HpackHuffmanDecoder implements ByteProcessor {
private static final byte HUFFMAN_EMIT_SYMBOL = 1 << 1;
private static final byte HUFFMAN_FAIL = 1 << 2;
private static final int HUFFMAN_COMPLETE_SHIFT = 1 << 8;
private static final int HUFFMAN_EMIT_SYMBOL_SHIFT = 1 << 9;
private static final int HUFFMAN_FAIL_SHIFT = 1 << 10;
private static final int HUFFMAN_COMPLETE_SHIFT = HUFFMAN_COMPLETE << 8;
private static final int HUFFMAN_EMIT_SYMBOL_SHIFT = HUFFMAN_EMIT_SYMBOL << 8;
private static final int HUFFMAN_FAIL_SHIFT = HUFFMAN_FAIL << 8;
/**
* A table of byte tuples (state, flags, output). They are packed together as:
@ -4672,7 +4672,6 @@ final class HpackHuffmanDecoder implements ByteProcessor {
private byte[] dest;
private int k;
private int state;
private int flags;
HpackHuffmanDecoder() { }
@ -4696,7 +4695,7 @@ final class HpackHuffmanDecoder implements ByteProcessor {
if (endIndex == -1) {
// We did consume the requested length
buf.readerIndex(readerIndex + length);
if ((flags & HUFFMAN_COMPLETE_SHIFT) != HUFFMAN_COMPLETE_SHIFT) {
if ((state & HUFFMAN_COMPLETE_SHIFT) != HUFFMAN_COMPLETE_SHIFT) {
throw BAD_ENCODING;
}
return new AsciiString(dest, 0, k, false);
@ -4710,7 +4709,6 @@ final class HpackHuffmanDecoder implements ByteProcessor {
dest = null;
k = 0;
state = 0;
flags = 0;
}
}
@ -4719,27 +4717,21 @@ final class HpackHuffmanDecoder implements ByteProcessor {
*/
@Override
public boolean process(byte input) {
int index = (state << 4) | ((input & 0xFF) >>> 4);
int row = HUFFS[index];
flags = row & 0x00FF00;
if ((flags & HUFFMAN_FAIL_SHIFT) != 0) {
return false;
}
if ((flags & HUFFMAN_EMIT_SYMBOL_SHIFT) != 0) {
dest[k++] = (byte) (row & 0xFF);
}
state = row >> 16;
return processNibble(input >> 4) && processNibble(input);
}
index = (state << 4) | (input & 0x0F);
row = HUFFS[index];
flags = row & 0x00FF00;
if ((flags & HUFFMAN_FAIL_SHIFT) != 0) {
private boolean processNibble(int input) {
// The high nibble of the flags byte of each row is always zero
// (low nibble after shifting row by 12), since there are only 3 flag bits
int index = state >> 12 | (input & 0x0F);
state = HUFFS[index];
if ((state & HUFFMAN_FAIL_SHIFT) != 0) {
return false;
}
if ((flags & HUFFMAN_EMIT_SYMBOL_SHIFT) != 0) {
dest[k++] = (byte) (row & 0xFF);
if ((state & HUFFMAN_EMIT_SYMBOL_SHIFT) != 0) {
// state is always positive so can cast without mask here
dest[k++] = (byte) state;
}
state = row >> 16;
return true;
}
}