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decode.cc
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decode.cc
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/*
Cauchy Prime Field Erasure Coding
Copyright 2024 Ahmet Inan <[email protected]>
*/
#include <set>
#include <cassert>
#include <cstdint>
#include <fstream>
#include <iostream>
#include "crc.hh"
#include "prime_field.hh"
#include "cauchy_prime_field_erasure_coding.hh"
int main(int argc, char **argv)
{
if (argc < 3) {
std::cerr << "usage: " << argv[0] << " OUTPUT CHUNKS.." << std::endl;
return 1;
}
int chunk_count = argc - 2;
typedef CODE::PrimeField<uint64_t, 65537> PF;
const int MAX_LEN = PF::P - 2;
uint16_t *chunk_ident = nullptr;
uint16_t *chunk_subst = nullptr;
uint16_t *chunk_data = nullptr;
int block_values = 0;
int block_count = 0;
int block_index = 0;
int output_bytes = 0;
uint32_t crc32_value = 0;
bool first = true;
std::set<uint16_t> list;
for (int i = 0; i < chunk_count; ++i) {
const char *chunk_name = argv[2+i];
std::ifstream chunk_file(chunk_name, std::ios::binary);
if (chunk_file.bad()) {
std::cerr << "Couldn't open file \"" << chunk_name << "\" for reading." << std::endl;
return 1;
}
char magic[3];
chunk_file.read(magic, 3);
uint16_t splits;
chunk_file.read(reinterpret_cast<char *>(&splits), 2);
uint16_t ident;
chunk_file.read(reinterpret_cast<char *>(&ident), 2);
uint16_t sub;
chunk_file.read(reinterpret_cast<char *>(&sub), 2);
int32_t size = 0;
chunk_file.read(reinterpret_cast<char *>(&size), 3);
uint32_t crc32;
chunk_file.read(reinterpret_cast<char *>(&crc32), 4);
int length = (size + 2 * splits + 2) / (2 * splits + 2);
if (!chunk_file || magic[0] != 'C' || magic[1] != 'P' || magic[2] != 'F' || splits >= 1024 || length > MAX_LEN || ident <= splits || list.count(ident)) {
std::cerr << "Skipping file \"" << chunk_name << "\"." << std::endl;
continue;
}
if (first) {
first = false;
block_count = splits + 1;
output_bytes = size + 1;
block_values = length;
crc32_value = crc32;
chunk_ident = new uint16_t[block_count];
chunk_subst = new uint16_t[block_count];
chunk_data = new uint16_t[block_count * block_values];
} else if (block_count != splits + 1 || output_bytes != size + 1 || crc32_value != crc32) {
std::cerr << "Skipping file \"" << chunk_name << "\"." << std::endl;
continue;
}
list.insert(ident);
chunk_ident[block_index] = ident;
chunk_subst[block_index] = sub;
chunk_file.read(reinterpret_cast<char *>(chunk_data + block_index * block_values), 2 * block_values);
if (++block_index >= block_count)
break;
}
if (block_index != block_count) {
std::cerr << "Need " << block_count << " valid chunks but only got " << block_index << "." << std::endl;
return 1;
}
const char *output_name = argv[1];
if (output_name[0] == '-' && output_name[1] == 0)
output_name = "/dev/stdout";
std::ofstream output_file(output_name, std::ios::binary | std::ios::trunc);
if (output_file.bad()) {
std::cerr << "Couldn't open file \"" << output_name << "\" for writing." << std::endl;
return 1;
}
uint16_t *output_data = new uint16_t[block_values];
auto cpf = new CODE::CauchyPrimeFieldErasureCoding<PF, uint16_t, MAX_LEN>();
static CODE::CRC<uint32_t> crc(0x8F6E37A0);
for (int i = 0, j = 0; i < block_count; ++i) {
cpf->decode(output_data, chunk_data, chunk_subst, chunk_ident, i, block_values, block_count);
int copy_bytes = 2 * block_values;
j += copy_bytes;
if (j > output_bytes)
copy_bytes -= j - output_bytes;
output_file.write(reinterpret_cast<char *>(output_data), copy_bytes);
for (int k = 0; k < copy_bytes; ++k)
crc(reinterpret_cast<uint8_t *>(output_data)[k]);
}
delete cpf;
delete[] chunk_subst;
delete[] chunk_ident;
delete[] output_data;
delete[] chunk_data;
if (crc() != crc32_value) {
std::cerr << "CRC value does not match!" << std::endl;
return 1;
}
return 0;
}