Skip to content

Commit b9e298f

Browse files
bwbeachbwbeach
committed
Add second coding loop, along with test to make sure
that all coding loops produce the same answers.
1 parent 6948472 commit b9e298f

File tree

4 files changed

+116
-34
lines changed

4 files changed

+116
-34
lines changed

‎src/main/java/com/backblaze/erasure/CodingLoop.java

Lines changed: 6 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -8,6 +8,12 @@
88

99
public interface CodingLoop {
1010

11+
CodingLoop[] ALL_CODING_LOOPS =
12+
new CodingLoop[] {
13+
new IndexShardInputExpCodingLoop(),
14+
new IndexShardInputTableCodingLoop()
15+
};
16+
1117
/**
1218
* Multiplies a subset of rows from a coding matrix by a full set of
1319
* input shards to produce some output shards.

‎src/main/java/com/backblaze/erasure/IndexShardInputTableCodingLoop.java

Lines changed: 81 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -0,0 +1,81 @@
1+
/**
2+
* One specific ordering/nesting of the coding loops.
3+
*
4+
* Copyright 2015, Backblaze, Inc. All rights reserved.
5+
*/
6+
7+
package com.backblaze.erasure;
8+
9+
public class IndexShardInputTableCodingLoop implements CodingLoop {
10+
11+
@Override
12+
public void codeSomeShards(
13+
byte[][] matrixRows,
14+
byte[][] inputs, int inputCount,
15+
byte[][] outputs, int outputCount,
16+
int offset, int byteCount) {
17+
18+
// This is the inner loop. It needs to be fast. Be careful
19+
// if you change it.
20+
//
21+
// Note that dataShardCount is final in the class, so the
22+
// compiler can load it just once, before the loop. Explicitly
23+
// adding a local variable does not make it faster.
24+
//
25+
// I have tried inlining Galois.multiply(), but it doesn't
26+
// make things any faster. The JIT compiler is known to inline
27+
// methods, so it's probably already doing so.
28+
//
29+
// This method has been timed and compared with a C implementation.
30+
// This Java version is only about 10% slower than C.
31+
32+
byte [] [] table = Galois.MULTIPLICATION_TABLE;
33+
for (int iByte = offset; iByte < offset + byteCount; iByte++) {
34+
for (int iRow = 0; iRow < outputCount; iRow++) {
35+
byte [] matrixRow = matrixRows[iRow];
36+
int value = 0;
37+
for (int c = 0; c < inputCount; c++) {
38+
value ^= table[matrixRow[c] & 0xFF][inputs[c][iByte] & 0xFF];
39+
}
40+
outputs[iRow][iByte] = (byte) value;
41+
}
42+
}
43+
}
44+
45+
@Override
46+
public boolean checkSomeShards(
47+
byte[][] matrixRows,
48+
byte[][] inputs, int inputCount,
49+
byte[][] toCheck, int checkCount,
50+
int offset, int byteCount) {
51+
52+
// This is the inner loop. It needs to be fast. Be careful
53+
// if you change it.
54+
//
55+
// Note that dataShardCount is final in the class, so the
56+
// compiler can load it just once, before the loop. Explicitly
57+
// adding a local variable does not make it faster.
58+
//
59+
// I have tried inlining Galois.multiply(), but it doesn't
60+
// make things any faster. The JIT compiler is known to inline
61+
// methods, so it's probably already doing so.
62+
//
63+
// This method has been timed and compared with a C implementation.
64+
// This Java version is only about 10% slower than C.
65+
66+
byte [] [] table = Galois.MULTIPLICATION_TABLE;
67+
for (int iByte = offset; iByte < offset + byteCount; iByte++) {
68+
for (int iRow = 0; iRow < checkCount; iRow++) {
69+
byte [] matrixRow = matrixRows[iRow];
70+
int value = 0;
71+
for (int c = 0; c < inputCount; c++) {
72+
value ^= table[matrixRow[c] & 0xFF][inputs[c][iByte] & 0xFF];
73+
}
74+
if (toCheck[iRow][iByte] != (byte) value) {
75+
return false;
76+
}
77+
}
78+
}
79+
return true;
80+
}
81+
}

‎src/main/java/com/backblaze/erasure/ReedSolomon.java

Lines changed: 0 additions & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -117,7 +117,6 @@ public boolean isParityCorrect(byte[][] shards, int firstByte, int byteCount) {
117117
firstByte, byteCount);
118118
}
119119

120-
121120
/**
122121
* Given a list of shards, some of which contain data, fills in the
123122
* ones that don't have data.

‎src/test/java/com/backblaze/erasure/ReedSolomonTest.java

Lines changed: 29 additions & 33 deletions
Original file line numberDiff line numberDiff line change
@@ -37,47 +37,43 @@ public void testZeroSizeEncode() {
3737

3838
/**
3939
* Make sure that the results on a tiny encoding match what
40-
* the prototype Python code did.
40+
* the prototype Python code did, and that all of the different
41+
* coding loops produce the same answers.
4142
*/
4243
@Test
4344
public void testOneEncode() {
44-
ReedSolomon codec = ReedSolomon.create(5, 5);
45-
byte [] [] shards = new byte[10] [];
46-
shards[0] = new byte [] {0, 1};
47-
shards[1] = new byte [] {4, 5};
48-
shards[2] = new byte [] {2, 3};
49-
shards[3] = new byte [] {6, 7};
50-
shards[4] = new byte [] {8, 9};
51-
shards[5] = new byte [2];
52-
shards[6] = new byte [2];
53-
shards[7] = new byte [2];
54-
shards[8] = new byte [2];
55-
shards[9] = new byte [2];
56-
codec.encodeParity(shards, 0, 2);
57-
assertArrayEquals(new byte [] {12 ,13}, shards[5]);
58-
assertArrayEquals(new byte [] {10 ,11}, shards[6]);
59-
assertArrayEquals(new byte [] {14 ,15}, shards[7]);
60-
assertArrayEquals(new byte [] {90 ,91}, shards[8]);
61-
assertArrayEquals(new byte [] {94 ,95}, shards[9]);
62-
63-
assertTrue(codec.isParityCorrect(shards, 0, 2));
64-
shards[8][0] += 1;
65-
assertFalse(codec.isParityCorrect(shards, 0, 2));
45+
for (CodingLoop codingLoop : CodingLoop.ALL_CODING_LOOPS) {
46+
ReedSolomon codec = new ReedSolomon(5, 5, codingLoop);
47+
byte[][] shards = new byte[10][];
48+
shards[0] = new byte[]{0, 1};
49+
shards[1] = new byte[]{4, 5};
50+
shards[2] = new byte[]{2, 3};
51+
shards[3] = new byte[]{6, 7};
52+
shards[4] = new byte[]{8, 9};
53+
shards[5] = new byte[2];
54+
shards[6] = new byte[2];
55+
shards[7] = new byte[2];
56+
shards[8] = new byte[2];
57+
shards[9] = new byte[2];
58+
codec.encodeParity(shards, 0, 2);
59+
assertArrayEquals(new byte[]{12, 13}, shards[5]);
60+
assertArrayEquals(new byte[]{10, 11}, shards[6]);
61+
assertArrayEquals(new byte[]{14, 15}, shards[7]);
62+
assertArrayEquals(new byte[]{90, 91}, shards[8]);
63+
assertArrayEquals(new byte[]{94, 95}, shards[9]);
64+
65+
assertTrue(codec.isParityCorrect(shards, 0, 2));
66+
shards[8][0] += 1;
67+
assertFalse(codec.isParityCorrect(shards, 0, 2));
68+
}
6669
}
6770

6871
/**
69-
* Try a simple case of encoding and decoding.
72+
* Checks that all of the coding loops produce the same results.
7073
*/
7174
@Test
72-
public void testSimpleEncodeDecode() {
73-
byte [] [] dataShards = new byte [] [] {
74-
new byte [] { 0, 1 },
75-
new byte [] { 1, 2 },
76-
new byte [] { 1, 3 },
77-
new byte [] { 2, 4 },
78-
new byte [] { 3, 5 }
79-
};
80-
runEncodeDecode(dataShards);
75+
public void testCodingLoopsProduceSameAnswers() {
76+
8177
}
8278

8379
/**

0 commit comments

Comments
 (0)