Struct q_compress::Prefix

#[non_exhaustive]
pub struct Prefix<T: NumberLike> {
    pub count: usize,
    pub code: Vec<bool>,
    pub lower: T,
    pub upper: T,
    pub run_len_jumpstart: Option<usize>,
    pub gcd: T::Unsigned,
}

A pairing of a Huffman code with a numerical range.

Quantile Compression works by splitting the distribution of numbers into ranges and associating a Huffman code (a short sequence of bits) with each range. The combination of these pieces of information, plus a couple others, is called a Prefix. When compressing a number, the compressor finds the prefix containing it, then writes out its Huffman code, optionally the number of consecutive repetitions of that number if run_length_jumpstart is available, and then the exact offset within the range for the number.

Fields (Non-exhaustive)

Non-exhaustive structs could have additional fields added in future. Therefore, non-exhaustive structs cannot be constructed in external crates using the traditional Struct { .. } syntax; cannot be matched against without a wildcard ..; and struct update syntax will not work.

count: usize

The count of numbers in the chunk that fall into this Prefix’s range. Not available in wrapped mode.

code: Vec<bool>

The Huffman code for this prefix. Collectively, all the prefixes for a chunk form a binary search tree (BST) over these Huffman codes. The BST over Huffman codes is different from the BST over numerical ranges.

lower: T

The lower bound for this prefix’s numerical range.

upper: T

The upper bound (inclusive) for this prefix’s numerical range.

run_len_jumpstart: Option<usize>

A parameter used for the most common prefix in a sparse distribution. For instance, if 90% of a chunk’s numbers are exactly 7, then the prefix for the range [7, 7] will have a run_len_jumpstart. The jumpstart value tunes the varint encoding of the number of consecutive repetitions of the prefix.

gcd: T::Unsigned

The greatest common divisor of all numbers belonging to this prefix (in the data type’s corresponding unsigned integer).

Trait Implementations

impl<T: Clone + NumberLike> Clone for Prefix<T>where T::Unsigned: Clone,

fn clone(&self) -> Prefix<T>

Returns a copy of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl<T: Debug + NumberLike> Debug for Prefix<T>where T::Unsigned: Debug,

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.

impl<T: NumberLike> Display for Prefix<T>

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.

impl<T: PartialEq + NumberLike> PartialEq<Prefix<T>> for Prefix<T>where T::Unsigned: PartialEq,

fn eq(&self, other: &Prefix<T>) -> bool

This method tests for self and other values to be equal, and is used by ==.

fn ne(&self, other: &Rhs) -> bool

This method tests for !=. The default implementation is almost always sufficient, and should not be overridden without very good reason.

impl<T: Eq + NumberLike> Eq for Prefix<T>where T::Unsigned: Eq,

impl<T: NumberLike> StructuralEq for Prefix<T>

impl<T: NumberLike> StructuralPartialEq for Prefix<T>