delta_encoding/
decoder.rs

1use num_traits::WrappingAdd;
2
3/// Construct a delta-decoder
4#[derive(Debug, Default, Copy, Clone)]
5pub struct DeltaDecoder<T> {
6    current: T,
7}
8
9impl<T: WrappingAdd + Copy> DeltaDecoder<T> {
10    pub fn decode(&mut self, value: T) -> T {
11        self.current = self.current.wrapping_add(&value);
12        self.current
13    }
14}
15
16/// A utility struct to construct a delta-decoder sequence from an iterator.
17#[derive(Clone, Debug)]
18#[must_use = "iterator adaptors are lazy and do nothing unless consumed"]
19pub struct DeltaDecoderIter<I>
20where
21    I: Iterator,
22    <I as Iterator>::Item: WrappingAdd + Copy,
23{
24    iter: I,
25    decoder: DeltaDecoder<I::Item>,
26}
27
28impl<I> Iterator for DeltaDecoderIter<I>
29where
30    I: Iterator,
31    <I as Iterator>::Item: WrappingAdd + Copy,
32{
33    type Item = I::Item;
34
35    fn next(&mut self) -> Option<Self::Item> {
36        Some(self.decoder.decode(self.iter.next()?))
37    }
38
39    fn size_hint(&self) -> (usize, Option<usize>) {
40        self.iter.size_hint()
41    }
42}
43
44impl<I> ExactSizeIterator for DeltaDecoderIter<I>
45where
46    I: ExactSizeIterator,
47    <I as Iterator>::Item: WrappingAdd + Copy,
48{
49}
50
51pub trait DeltaDecoderExt: Iterator
52where
53    <Self as Iterator>::Item: Default + Copy + WrappingAdd,
54{
55    /// Construct a delta-decoded iterator from an iterator.
56    /// The first element of the iterator is used as the starting point for the delta-encoding.
57    /// Note that unlike the [`DeltaDecoder.decode`] method, this method will panic if the delta is too large.
58    ///
59    /// ## Example
60    /// ```
61    /// use delta_encoding::DeltaDecoderExt;
62    ///
63    /// // Consuming original data into a delta-decoded iterator.
64    /// let mut decoded: Vec<i64> = vec![1, 1, 3, -1, -2].into_iter().original().collect();
65    /// assert_eq!(decoded, vec![1, 2, 5, 4, 2]);
66    ///
67    /// // Non-consuming original data, but avoiding the allocation of a new vector.
68    /// let mut decoded: Vec<i64> = vec![1, 1, 3, -1, -2].iter().copied().original().collect();
69    /// assert_eq!(decoded, vec![1, 2, 5, 4, 2]);
70    /// ```
71    fn original(self) -> DeltaDecoderIter<Self>
72    where
73        Self: Sized,
74    {
75        DeltaDecoderIter {
76            iter: self,
77            decoder: DeltaDecoder::default(),
78        }
79    }
80}
81
82impl<I> DeltaDecoderExt for I
83where
84    I: Iterator,
85    <I as Iterator>::Item: Default + Copy + WrappingAdd,
86{
87}
88
89#[cfg(test)]
90mod tests {
91    use super::*;
92    use crate::tests::TEST_DATA;
93
94    fn run(original: &[i64], encoded: &[i64]) {
95        let mut dec = DeltaDecoder::default();
96        let result: Vec<i64> = encoded.iter().map(|&v| dec.decode(v)).collect();
97        assert_eq!(result, original, "decoded from: {encoded:?}");
98
99        let result: Vec<i64> = encoded.iter().copied().original().collect();
100        assert_eq!(result, original, "iter().copied() encoded: {encoded:?}");
101    }
102
103    #[test]
104    fn test() {
105        for &(original, encoded) in TEST_DATA {
106            run(original, encoded);
107        }
108    }
109}
delta_encoding/decoder.rs

delta_encoding/
decoder.rs
