86 lines
2.6 KiB
Rust
86 lines
2.6 KiB
Rust
/// A function for splitting a list into N pieces.
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///
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/// We have titled it the "honey badger split" because of its robustness. It don't care.
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/// Iterator for the honey_badger_split function
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pub struct Split<'a, T: 'a> {
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n: usize,
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current_pos: usize,
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list: &'a [T],
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list_length: usize,
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}
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impl<'a, T> Iterator for Split<'a, T> {
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type Item = &'a [T];
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fn next(&mut self) -> Option<Self::Item> {
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self.current_pos += 1;
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if self.current_pos <= self.n {
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match self.list.get(
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self.list_length * (self.current_pos - 1) / self.n
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..self.list_length * self.current_pos / self.n,
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) {
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Some(v) => Some(v),
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None => unreachable!(),
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}
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} else {
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None
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}
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}
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}
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/// Splits a slice into chunks of size n. All postive n values are applicable,
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/// hence the honey_badger prefix.
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///
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/// Returns an iterator over the original list.
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pub trait SplitExt<T> {
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fn honey_badger_split(&self, n: usize) -> Split<T>;
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}
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impl<T> SplitExt<T> for [T] {
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fn honey_badger_split(&self, n: usize) -> Split<T> {
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Split {
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n,
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current_pos: 0,
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list: &self,
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list_length: self.len(),
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}
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}
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}
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#[cfg(test)]
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mod tests {
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use super::*;
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#[test]
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fn test_honey_badger_split() {
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/*
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* These test cases are generated from the eth2.0 spec `split()`
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* function at commit cbd254a.
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*/
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let input: Vec<usize> = vec![0, 1, 2, 3];
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let output: Vec<&[usize]> = input.honey_badger_split(2).collect();
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assert_eq!(output, vec![&[0, 1], &[2, 3]]);
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let input: Vec<usize> = vec![0, 1, 2, 3];
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let output: Vec<&[usize]> = input.honey_badger_split(6).collect();
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let expected: Vec<&[usize]> = vec![&[], &[0], &[1], &[], &[2], &[3]];
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assert_eq!(output, expected);
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let input: Vec<usize> = vec![0, 1, 2, 3];
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let output: Vec<&[usize]> = input.honey_badger_split(10).collect();
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let expected: Vec<&[usize]> = vec![&[], &[], &[0], &[], &[1], &[], &[], &[2], &[], &[3]];
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assert_eq!(output, expected);
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let input: Vec<usize> = vec![0];
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let output: Vec<&[usize]> = input.honey_badger_split(5).collect();
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let expected: Vec<&[usize]> = vec![&[], &[], &[], &[], &[0]];
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assert_eq!(output, expected);
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let input: Vec<usize> = vec![0, 1, 2];
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let output: Vec<&[usize]> = input.honey_badger_split(2).collect();
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let expected: Vec<&[usize]> = vec![&[0], &[1, 2]];
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assert_eq!(output, expected);
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}
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}
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