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stir the hash state a little to avoid prefix collisions

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The 8472 2024-07-03 22:54:15 +02:00
parent dd509c7a63
commit f21683432b
1 changed files with 9 additions and 4 deletions
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13
library/std/src/path.rs
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@ -3098,15 +3098,19 @@ fn hash<H: Hasher>(&self, h: &mut H) {
let bytes = &bytes[prefix_len..];
let mut component_start = 0;
let mut bytes_hashed = 0;
// track some extra state to avoid prefix collisions.
// ["foo", "bar"] and ["foobar"], will have the same payload bytes
// but result in different chunk_bits
let mut chunk_bits: usize = 0;
for i in 0..bytes.len() {
let is_sep = if verbatim { is_verbatim_sep(bytes[i]) } else { is_sep_byte(bytes[i]) };
if is_sep {
if i > component_start {
let to_hash = &bytes[component_start..i];
chunk_bits = chunk_bits.wrapping_add(to_hash.len());
chunk_bits = chunk_bits.rotate_right(2);
h.write(to_hash);
bytes_hashed += to_hash.len();
}
// skip over separator and optionally a following CurDir item
@ -3127,11 +3131,12 @@ fn hash<H: Hasher>(&self, h: &mut H) {
if component_start < bytes.len() {
let to_hash = &bytes[component_start..];
chunk_bits = chunk_bits.wrapping_add(to_hash.len());
chunk_bits = chunk_bits.rotate_right(2);
h.write(to_hash);
bytes_hashed += to_hash.len();
}
h.write_usize(bytes_hashed);
h.write_usize(chunk_bits);
}
}