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pub fn shift_and_single_masks(pattern: &[u8]) -> (Vec<usize>, usize, usize) {
let mut masks = vec![0; 256];
let mut bit = 1;
for c in pattern {
masks[*c as usize] |= bit;
bit *= 2;
}
(masks, 1, bit / 2)
}
fn shift_and_with_masks(
text: &[u8],
masks: &[usize],
ones: usize,
accept: usize,
) -> Vec<(usize, usize)> {
let mut res = Vec::new();
let mut active: usize = 0;
for (i, c) in text.iter().enumerate() {
active = ((active << 1) | ones) & masks[*c as usize];
let found = active & accept;
if found != 0 {
res.push((i, found));
}
}
res
}
pub fn shift_and(pattern: &[u8], text: &[u8]) -> Vec<usize> {
let mut res = Vec::new();
let m = pattern.len();
let (mask, ones, accept) = shift_and_single_masks(pattern);
for (i, _) in shift_and_with_masks(text, &mask, ones, accept) {
res.push(i - m + 1);
}
res
}
#[cfg(test)]
mod tests {
use super::*;
#[test]
fn test_shift_and() {
let text = "gccttaacattattacgccta".as_bytes();
let pattern = "tta".as_bytes();
let mut matches = shift_and(pattern, text);
matches.sort_unstable();
let matches_correct = vec![3, 9, 12];
assert_eq!(matches, matches_correct);
}
}