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chunker.rs: make sure chunk_size_avg is a power of two

This commit is contained in:
Dietmar Maurer 2019-01-03 15:10:54 +01:00
parent ea4ea34baf
commit 050f8a6355
1 changed files with 8 additions and 5 deletions
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13
src/backup/chunker.rs
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@ -97,9 +97,10 @@ const BUZHASH_TABLE: [u32; 256] = [
impl Chunker {
/// Create a new Chunker instance, which produces and average chunk
/// size of `chunk_size_avg`. We allow variation from
/// `chunk_size_avg/4` up to a maximum of `chunk_size_avg*4`.
/// Create a new Chunker instance, which produces and average
/// chunk size of `chunk_size_avg` (need to be a power of two). We
/// allow variation from `chunk_size_avg/4` up to a maximum of
/// `chunk_size_avg*4`.
pub fn new(chunk_size_avg: usize) -> Self {
// The chunk cut discriminator. In order to get an average
// chunk size of avg, we cut whenever for a hash value "h" at
@ -112,9 +113,11 @@ impl Chunker {
let avg = chunk_size_avg as f64;
let discriminator = (avg / (-1.42888852e-7 * avg + 1.33237515)) as u32;
let break_test_value = (chunk_size_avg*2 -1) as u32;
if chunk_size_avg.count_ones() != 1 {
panic!("got unexpected chunk size - not a power of two.");
}
println!("DISCRIMINATOR: {} {}", discriminator, avg/1.33);
let break_test_value = (chunk_size_avg*2 -1) as u32;
Self {
h: 0,