Erasure duplicate makes decoder to fail
Hi-Angel opened this issue · comments
Steps to reproduce
code:
#include <ezpwd/rs>
#include <array>
#include <cstdint>
#include <vector>
using namespace std;
const ushort sz_codeword = 255,
sz_payload = 128,
sz_parity = sz_codeword - sz_payload;
const array<uint8_t, sz_codeword> rs_block_original = {
0x6d, 0xde, 0x8c, 0x66, 0x05, 0x6a, 0x63, 0xd0, 0x7e, 0xa0, 0x9e, 0xed, 0xe9, 0xa6, 0x66, 0x5f,
0x11, 0xde, 0x8c, 0xf1, 0x99, 0x70, 0x76, 0x27, 0x3b, 0x9f, 0xc1, 0xc8, 0xb4, 0xbc, 0x52, 0x86,
0x53, 0x3c, 0x6e, 0xe6, 0x0e, 0xff, 0xca, 0x4e, 0x41, 0x5d, 0x49, 0x90, 0x6c, 0x88, 0x5f, 0xa3,
0xea, 0xbb, 0xa1, 0x4d, 0x42, 0xe1, 0x79, 0xcc, 0x23, 0xd2, 0xf6, 0x86, 0xb0, 0x85, 0x72, 0x5b,
0xba, 0xa4, 0x19, 0x0c, 0xc9, 0x2d, 0xda, 0x38, 0xfa, 0xfd, 0x2b, 0x19, 0x81, 0x3e, 0x74, 0x49,
0xa6, 0x27, 0x07, 0xbb, 0xaa, 0xe7, 0x34, 0x96, 0xe8, 0x8a, 0xac, 0xee, 0x6e, 0xef, 0xb1, 0x39,
0xe5, 0x63, 0xdb, 0x66, 0xa2, 0xd3, 0xaf, 0xe8, 0x10, 0x88, 0x4b, 0x2c, 0xac, 0x19, 0x44, 0x7c,
0x57, 0xda, 0xcd, 0xfb, 0x75, 0xa1, 0xe6, 0x6d, 0x4d, 0x4a, 0xb0, 0xdd, 0xa9, 0x88, 0x76, 0xce,
0xcc, 0x7f, 0xd7, 0xd5, 0xe1, 0xc7, 0x02, 0x7b, 0x10, 0x12, 0x84, 0x21, 0xb9, 0x37, 0xbb, 0x91,
0x16, 0x94, 0x04, 0x80, 0x21, 0xe8, 0xaf, 0x8e, 0xa1, 0xee, 0xb6, 0x17, 0x33, 0x60, 0x78, 0x06,
0xce, 0x2b, 0x7c, 0x1c, 0x03, 0x0e, 0x92, 0x82, 0xf1, 0x87, 0x1a, 0x72, 0xb1, 0x11, 0xc0, 0xe3,
0x7e, 0xe3, 0xdc, 0x32, 0x14, 0x8e, 0x06, 0xe2, 0xe4, 0xca, 0x97, 0x6e, 0x43, 0xe1, 0xdb, 0xd7,
0xa8, 0xb3, 0x46, 0xdb, 0x9e, 0xd0, 0xce, 0x51, 0xc3, 0xd3, 0x3d, 0x8f, 0xf5, 0xee, 0x31, 0x1c,
0x6f, 0xdf, 0xb6, 0xc9, 0x96, 0x2b, 0x26, 0x4d, 0x3b, 0xec, 0x25, 0x7a, 0x4c, 0x48, 0xd7, 0x49,
0xf3, 0x01, 0xb2, 0x6f, 0xe3, 0xcd, 0x03, 0xcf, 0x34, 0x4e, 0x31, 0x13, 0x6e, 0x84, 0x44, 0x5c,
0x94, 0x2c, 0x06, 0x5d, 0xb4, 0x45, 0xae, 0x7b, 0x8b, 0xcc, 0xf0, 0x14, 0xd8, 0x4f, 0x8d };
const array<uint8_t, sz_codeword> rs_block_with_erasures = {
0x6d, 0xde, 0x8c, 0x00, 0x00, 0x00, 0x63, 0xd0, 0x7e, 0xa0, 0x9e, 0xed, 0xe9, 0x00, 0x00, 0x5f,
0x11, 0xde, 0x8c, 0xf1, 0x99, 0x70, 0x00, 0x00, 0x00, 0x00, 0xc1, 0xc8, 0xb4, 0xbc, 0x52, 0x86,
0x00, 0x00, 0x00, 0xe6, 0x0e, 0xff, 0xca, 0x4e, 0x41, 0x5d, 0x00, 0x00, 0x00, 0x88, 0x5f, 0xa3,
0xea, 0xbb, 0xa1, 0x4d, 0x00, 0x00, 0x00, 0x00, 0x23, 0xd2, 0xf6, 0x86, 0xb0, 0x85, 0x00, 0x00,
0x00, 0xa4, 0x19, 0x0c, 0xc9, 0x2d, 0xda, 0x38, 0x00, 0x00, 0x00, 0x19, 0x81, 0x3e, 0x74, 0x49,
0xa6, 0x27, 0x00, 0x00, 0x00, 0x00, 0x34, 0x96, 0xe8, 0x8a, 0xac, 0xee, 0x00, 0x00, 0x00, 0x39,
0xe5, 0x63, 0xdb, 0x66, 0xa2, 0xd3, 0x00, 0x00, 0x00, 0x88, 0x4b, 0x2c, 0xac, 0x19, 0x44, 0x7c,
0x00, 0x00, 0x00, 0x00, 0x75, 0xa1, 0xe6, 0x6d, 0x4d, 0x4a, 0x00, 0x00, 0x00, 0x88, 0x76, 0xce,
0xcc, 0x7f, 0xd7, 0xd5, 0x00, 0x00, 0x00, 0x7b, 0x10, 0x12, 0x84, 0x21, 0xb9, 0x37, 0x00, 0x00,
0x00, 0x00, 0x04, 0x80, 0x21, 0xe8, 0xaf, 0x8e, 0x00, 0x00, 0x00, 0x17, 0x33, 0x60, 0x78, 0x06,
0xce, 0x2b, 0x00, 0x00, 0x00, 0x0e, 0x92, 0x82, 0xf1, 0x87, 0x1a, 0x72, 0x00, 0x00, 0x00, 0x00,
0x7e, 0xe3, 0xdc, 0x32, 0x14, 0x8e, 0x00, 0x00, 0x00, 0xca, 0x97, 0x6e, 0x43, 0xe1, 0xdb, 0xd7,
0x00, 0x00, 0x00, 0xdb, 0x9e, 0xd0, 0xce, 0x51, 0xc3, 0xd3, 0x00, 0x00, 0x00, 0x00, 0x31, 0x1c,
0x6f, 0xdf, 0xb6, 0xc9, 0x00, 0x00, 0x00, 0x4d, 0x3b, 0xec, 0x25, 0x7a, 0x4c, 0x48, 0x00, 0x00,
0x00, 0x01, 0xb2, 0x6f, 0xe3, 0xcd, 0x03, 0xcf, 0x00, 0x00, 0x00, 0x00, 0x6e, 0x84, 0x44, 0x5c,
0x94, 0x2c, 0x00, 0x00, 0x00, 0x45, 0xae, 0x7b, 0x8b, 0xcc, 0xf0, 0x14, 0x00, 0x00, 0x00 };
const array<int, 86> erasures_pos = { 3, 4, 5, 13, 13, 14, 22, 23, 24, 25, 32, 33, 34, 42, 43, 44, 52, 53,
54, 55, 62, 63, 64, 72, 73, 74, 82, 83, 84, 85, 92, 93, 94, 102, 103,
104, 112, 113, 114, 115, 122, 123, 124, 132, 133, 134, 142, 143, 144,
145, 152, 153, 154, 162, 163, 164, 172, 173, 174, 175, 182, 183, 184,
192, 193, 194, 202, 203, 204, 205, 212, 213, 214, 222, 223, 224, 232,
233, 234, 235, 242, 243, 244, 252, 253, 254 };
int main() {
ezpwd::RS<sz_codeword, sz_payload> rs;
auto data = vector<uint8_t>(rs_block_with_erasures.begin(), rs_block_with_erasures.end()),
original = vector<uint8_t>(rs_block_original.begin(), rs_block_original.end());
auto erasures = vector<int>(erasures_pos.begin(), erasures_pos.end());
int fixed = rs.decode(data, erasures);
if (fixed == -1 && data != original)
puts("Decoding failed!");
}building'n'running;
$ g++ test.cpp -o a -g3 -O0 -Wall -Wextra -Wsign-conversion -std=c++17 -pedantic -fsanitize=address -isystem/usr/include/ezpwd-reed-solomon
$ ./a
Decoding failed!
$ sed -i "s/86> erasures_pos = { 3, 4, 5, 13, 13, /85> erasures_pos = { 3, 4, 5, 13, /g" test.cpp
$ g++ test.cpp -o a -g3 -O0 -Wall -Wextra -Wsign-conversion -std=c++17 -pedantic -fsanitize=address -isystem/usr/include/ezpwd-reed-solomon
$ ./a
The reason for fail is duplicate erasure position 13, 13, which is removed as part of the steps. I'm not sure if it's expected behavior.
Yes, it doesn't handle duplicate erasure positions; good catch. This is inherited behaviour from the original Phil Karn implementation. I don't know if it's worthwhile sorting and uniquing the incoming erasure position vector; I think it should remain an error: the erasure positions should be unique. This should be documented.
I don't know if it's worthwhile sorting and uniquing the incoming erasure position vector; I think it should remain an error: the erasure positions should be unique. This should be documented.
Agree, sorting and uniquing would take unnecessary overhead, in this case it's better to leave to users. It's just that I thought it would come without the cost — like, restoring same position twice is the same as once. But granted, I don't know implementation details.
To be honest, in my case it revealed a bug. I imagine it could be nice to have the check, say, for debug mode only — just for a user to see they did something wrong. Otherwise all they see would be ezpwd failing to decode a block — "why? who knows".