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Resolve ambiguity about graph construction

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Christopher Berner 2019-02-11 17:59:10 -08:00
parent f8d8d53c52
commit e84bdfbd41
1 changed files with 19 additions and 6 deletions
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25
src/base.rs
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@ -159,12 +159,12 @@ impl IntermediateSymbolDecoder {
}
let mut ones = vec![];
for col in self.i..(self.L - self.u) {
// XXX: It's unclear exactly how to construct this graph. The RFC seems to have
// a typo. It says, emphasis mine, "The following graph defined by the structure
// of V is used in determining which row of A is chosen. The columns that
// intersect V are the nodes in the graph, and the rows that have *exactly 2
// nonzero* entries in V and are not HDPC rows are the edges of the graph that
// connect the two columns (nodes) in the positions of *the two ones*."
// "The following graph defined by the structure of V is used in determining which
// row of A is chosen. The columns that intersect V are the nodes in the graph,
// and the rows that have exactly 2 nonzero entries in V and are not HDPC rows
// are the edges of the graph that connect the two columns (nodes) in the positions
// of the two ones."
// This part of the matrix is over GF(2), so "nonzero entries" is equivalent to "ones"
if self.A.get(row, col) == Octet::one() {
ones.push(col);
}
@ -272,6 +272,8 @@ impl IntermediateSymbolDecoder {
if r == 2 {
// See paragraph starting "If r = 2 and there is a row with exactly 2 ones in V..."
if rows_with_two_ones.len() > 0 {
#[cfg(debug_assertions)]
self.first_phase_graph_substep_verify(self.i, self.L, &hdpc_rows, &rows_with_two_ones, &non_zero_counts);
chosen_row = Some(self.first_phase_graph_substep(&rows_with_two_ones, &hdpc_rows));
}
else {
@ -331,6 +333,17 @@ impl IntermediateSymbolDecoder {
return true;
}
// Verify there there are no non-HPDC rows with exactly two non-zero entries, greater than one
#[inline(never)]
#[cfg(debug_assertions)]
fn first_phase_graph_substep_verify(&self, start_row: usize, end_row: usize, hdpc_rows: &Vec<bool>, rows_with_two_ones: &Vec<usize>, non_zeros: &ArrayMap<u32>) {
for row in start_row..end_row {
if non_zeros.get(row) == 2 {
assert!(rows_with_two_ones.contains(&row) || hdpc_rows[row]);
}
}
}
// See section 5.4.2.2. Verifies the two all-zeros submatrices and the identity submatrix
#[inline(never)]
#[cfg(debug_assertions)]