crossword 0.2.0

Library for crossword puzzles including .puz file parsing
Documentation 
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33

//! Checksum logic. See
//! <https://gist.github.com/sliminality/dab21fa834eae0a70193c7cd69c356d5#checksums>

#[must_use]
pub(crate) fn checksum_region(base: &[u8], input_checksum: u16) -> u16 {
  let mut checksum = input_checksum;
  for &byte in base {
    if checksum & 0x0001_u16 != 0 {
      checksum = (checksum >> 1) + 0x8000
    } else {
      checksum = checksum >> 1;
    }
    checksum = checksum.overflowing_add(byte as u16).0;
  }
  checksum
}

/// For metadata (title, author, copyright, or notes), we do nothing if the string is
/// empty, but if it's not empty we include the \0 byte in the calculation.
#[must_use]
pub(crate) fn checksum_metadata_string(s: &[u8], input_checksum: u16) -> u16 {
  if s == b"\0" {
    return input_checksum;
  }

  checksum_region(s, input_checksum)
}

/// For clues, we do not include the trailing \0 byte.
#[must_use]
pub(crate) fn checksum_clue(s: &[u8], input_checksum: u16) -> u16 {
  checksum_region(&s[0..s.len() - 1], input_checksum)
}