test for prefix free codes, shows it's still broken

src/huff0/huff0_encoder.rs

@@ -1,5 +1,6 @@
 use alloc::vec::Vec;
 use core::cmp::Ordering;
+use std::eprintln;
 
 use crate::encoding::bit_writer::BitWriter;
 
@@ -13,7 +14,8 @@ impl HuffmanEncoder {
  for symbol in data {
  let (code, mut num_bits) = self.table.codes[*symbol as usize];
  while num_bits > 0 {
- let read = self.writer
+ let read = self
+ .writer
  .write_bits(&code.to_le_bytes(), num_bits as usize);
  num_bits -= read as u8;
  }
@@ -97,16 +99,12 @@ impl HuffmanTable {
  }
  let max_num_bits = highest_bit_set(weight_sum) - 1; // this is a log_2 of a clean power of two
 
- let mut start_value = 0;
  let mut current_value = 0;
  let mut current_weight = 0;
  let mut current_num_bits = 0;
  for entry in sorted.iter() {
  if current_weight != entry.weight {
- let count = sorted.iter().filter(|e| e.weight == entry.weight).count();
- current_value = start_value;
- start_value += count;
- start_value /= 2;
+ current_value = current_value / 2;
  current_weight = entry.weight;
  current_num_bits = max_num_bits - entry.weight + 1;
  }
@@ -238,6 +236,19 @@ fn weights() {
  "{} {weights:?}",
  max_weight
  );
+
+ let codes = HuffmanTable::build_from_weights(&weights).codes;
+ for (code, num_bits) in codes.iter().copied() {
+ for (code2, num_bits2) in codes.iter().copied() {
+ if num_bits == 0 || num_bits2 == 0 || (code, num_bits) == (code2, num_bits2) {
+ continue;
+ }
+ if num_bits <= num_bits2 {
+ let code2_shifted = code2 >> (num_bits2 - num_bits);
+ assert_ne!(code, code2_shifted, "{:b},{num_bits:} is prefix of {:b},{num_bits2:}", code, code2);
+ }
+ }
+ }
  }
 }