1
  2
  3
  4
  5
  6
  7
  8
  9
 10
 11
 12
 13
 14
 15
 16
 17
 18
 19
 20
 21
 22
 23
 24
 25
 26
 27
 28
 29
 30
 31
 32
 33
 34
 35
 36
 37
 38
 39
 40
 41
 42
 43
 44
 45
 46
 47
 48
 49
 50
 51
 52
 53
 54
 55
 56
 57
 58
 59
 60
 61
 62
 63
 64
 65
 66
 67
 68
 69
 70
 71
 72
 73
 74
 75
 76
 77
 78
 79
 80
 81
 82
 83
 84
 85
 86
 87
 88
 89
 90
 91
 92
 93
 94
 95
 96
 97
 98
 99
100
101
102
103
104
105
106
107
108
109
110

extern crate libc;

/// Implementation of the Opus range encoder.
pub mod opus {
    /// A c2rust-ified version of the Opus range decoder.
    mod imported_decode;
    mod imported_encode;

    mod encode;
    mod decode;

    pub use self::encode::Writer;
    pub use self::decode::Reader;
}

/// A trivial container representing the fact that a symbol may need to be defined.
pub struct AlreadyEncountered(pub bool);


#[derive(Clone)]
pub struct Segment {
    /// First value part of the segment.
    low: u32,

    /// First value >= low **not** part of the segment.
    next: u32,

    /// `true` if we have already returned at least one instance of this Segment.
    already_encountered: bool,
}
impl Segment {
    pub fn new(low: u32, next: u32) -> Segment {
        Segment {
            low,
            next,
            already_encountered: false
        }
    }
}

pub struct IndexedSegment {
    pub segment: Segment,
    pub index: usize,
}

pub struct CumulativeDistributionFrequency {
    /// Ordered, non-empty, contiguous list of segments, starting at 0.
    segments: Box<[Segment]>,

    /// The width, which is exactly `segments.last.width`.
    width: u32,
}
impl CumulativeDistributionFrequency {
    // FIXME: Better errors
    pub fn new(probabilities: Vec<u32>) -> Result<Self, ()> {
        if probabilities.len() == 0 {
            return Err(())
        }

        let mut segments = Vec::with_capacity(probabilities.len());
        let mut start = 0;
        for probability in probabilities {
            let next = start + probability;
            segments.push(Segment::new(start, next));
            start = next;
        }
        Ok(Self {
            segments: segments
                .into_boxed_slice(),
            width: start,
        })
    }

    /// Return the total frequency of symbols in this distribution.
    pub fn width(&self) -> u32 {
        self.width
    }

    /// Find a value from its frequency.
    pub fn find(&self, probability: u32) -> Option<IndexedSegment> {
        if probability >= self.width {
            return None
        }
        let index = self.segments.binary_search_by(|segment| {
            use std::cmp::Ordering;
            if segment.low > probability {
                return Ordering::Greater
            }
            if segment.next <= probability {
                return Ordering::Less
            }
            Ordering::Equal
        }).ok()?;
        Some(IndexedSegment {
            index,
            segment: self.segments[index].clone()
        })
    }

    /// Find a value from its index
    pub fn at_index(&mut self, index: usize) -> Option<Segment> {
        if index >= self.segments.len() {
            return None;
        }
        let ref mut segment = self.segments[index];
        let result = segment.clone();
        segment.already_encountered = true;
        Some(result)
    }
}