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//! Row format as defined in `arrow-rs`.
//! This currently partially implements that format only for needed types.
//! For completeness sake the format as defined by `arrow-rs` is as followed:
//! Converts [`ArrayRef`] columns into a [row-oriented](self) format.
//!
//! ## Overview
//!
//! The row format is a variable length byte sequence created by
//! concatenating the encoded form of each column. The encoding for
//! each column depends on its datatype (and sort options).
//!
//! The encoding is carefully designed in such a way that escaping is
//! unnecessary: it is never ambiguous as to whether a byte is part of
//! a sentinel (e.g. null) or a value.
//!
//! ## Unsigned Integer Encoding
//!
//! A null integer is encoded as a `0_u8`, followed by a zero-ed number of bytes corresponding
//! to the integer's length.
//!
//! A valid integer is encoded as `1_u8`, followed by the big-endian representation of the
//! integer.
//!
//! ```text
//! ┌──┬──┬──┬──┐ ┌──┬──┬──┬──┬──┐
//! 3 │03│00│00│00│ │01│00│00│00│03│
//! └──┴──┴──┴──┘ └──┴──┴──┴──┴──┘
//! ┌──┬──┬──┬──┐ ┌──┬──┬──┬──┬──┐
//! 258 │02│01│00│00│ │01│00│00│01│02│
//! └──┴──┴──┴──┘ └──┴──┴──┴──┴──┘
//! ┌──┬──┬──┬──┐ ┌──┬──┬──┬──┬──┐
//! 23423 │7F│5B│00│00│ │01│00│00│5B│7F│
//! └──┴──┴──┴──┘ └──┴──┴──┴──┴──┘
//! ┌──┬──┬──┬──┐ ┌──┬──┬──┬──┬──┐
//! NULL │??│??│??│??│ │00│00│00│00│00│
//! └──┴──┴──┴──┘ └──┴──┴──┴──┴──┘
//!
//! 32-bit (4 bytes) Row Format
//! Value Little Endian
//! ```
//!
//! ## Signed Integer Encoding
//!
//! Signed integers have their most significant sign bit flipped, and are then encoded in the
//! same manner as an unsigned integer.
//!
//! ```text
//! ┌──┬──┬──┬──┐ ┌──┬──┬──┬──┐ ┌──┬──┬──┬──┬──┐
//! 5 │05│00│00│00│ │05│00│00│80│ │01│80│00│00│05│
//! └──┴──┴──┴──┘ └──┴──┴──┴──┘ └──┴──┴──┴──┴──┘
//! ┌──┬──┬──┬──┐ ┌──┬──┬──┬──┐ ┌──┬──┬──┬──┬──┐
//! -5 │FB│FF│FF│FF│ │FB│FF│FF│7F│ │01│7F│FF│FF│FB│
//! └──┴──┴──┴──┘ └──┴──┴──┴──┘ └──┴──┴──┴──┴──┘
//!
//! Value 32-bit (4 bytes) High bit flipped Row Format
//! Little Endian
//! ```
//!
//! ## Float Encoding
//!
//! Floats are converted from IEEE 754 representation to a signed integer representation
//! by flipping all bar the sign bit if they are negative after normalizing nans
//! and signed zeros to a canonical representation.
//!
//! They are then encoded in the same manner as a signed integer.
//!
//! ## Fixed Length Bytes Encoding
//!
//! Fixed length bytes are encoded in the same fashion as primitive types above.
//!
//! For a fixed length array of length `n`:
//!
//! A null is encoded as `0_u8` null sentinel followed by `n` `0_u8` bytes
//!
//! A valid value is encoded as `1_u8` followed by the value bytes
//!
//! ## Variable Length Bytes (including Strings) Encoding
//!
//! A null is encoded as a `0_u8`.
//!
//! An empty byte array is encoded as `1_u8`.
//!
//! A non-null, non-empty byte array is encoded as `2_u8` followed by the byte array
//! encoded using a block based scheme described below.
//!
//! The byte array is broken up into 32-byte blocks, each block is written in turn
//! to the output, followed by `0xFF_u8`. The final block is padded to 32-bytes
//! with `0_u8` and written to the output, followed by the un-padded length in bytes
//! of this final block as a `u8`.
//!
//! Note the following example encodings use a block size of 4 bytes,
//! as opposed to 32 bytes for brevity:
//!
//! ```text
//! ┌───┬───┬───┬───┬───┬───┐
//! "MEEP" │02 │'M'│'E'│'E'│'P'│04 │
//! └───┴───┴───┴───┴───┴───┘
//!
//! ┌───┐
//! "" │01 |
//! └───┘
//!
//! NULL ┌───┐
//! │00 │
//! └───┘
//!
//! "Defenestration" ┌───┬───┬───┬───┬───┬───┐
//! │02 │'D'│'e'│'f'│'e'│FF │
//! └───┼───┼───┼───┼───┼───┤
//! │'n'│'e'│'s'│'t'│FF │
//! ├───┼───┼───┼───┼───┤
//! │'r'│'a'│'t'│'r'│FF │
//! ├───┼───┼───┼───┼───┤
//! │'a'│'t'│'i'│'o'│FF │
//! ├───┼───┼───┼───┼───┤
//! │'n'│00 │00 │00 │01 │
//! └───┴───┴───┴───┴───┘
//! ```
//!
//! This approach is loosely inspired by [COBS] encoding, and chosen over more traditional
//! [byte stuffing] as it is more amenable to vectorisation, in particular AVX-256.
//!
//! ## Dictionary Encoding
//!
//! [`RowsEncoded`] needs to support converting dictionary encoded arrays with unsorted, and
//! potentially distinct dictionaries. One simple mechanism to avoid this would be to reverse
//! the dictionary encoding, and encode the array values directly, however, this would lose
//! the benefits of dictionary encoding to reduce memory and CPU consumption.
//!
//! As such the [`RowsEncoded`] creates an order-preserving mapping
//! for each dictionary encoded column, which allows new dictionary
//! values to be added whilst preserving the sort order.
//!
//! A null dictionary value is encoded as `0_u8`.
//!
//! A non-null dictionary value is encoded as `1_u8` followed by a null-terminated byte array
//! key determined by the order-preserving dictionary encoding
//!
//! ```text
//! ┌──────────┐ ┌─────┐
//! │ "Bar" │ ───────────────▶│ 01 │
//! └──────────┘ └─────┘
//! ┌──────────┐ ┌─────┬─────┐
//! │"Fabulous"│ ───────────────▶│ 01 │ 02 │
//! └──────────┘ └─────┴─────┘
//! ┌──────────┐ ┌─────┐
//! │ "Soup" │ ───────────────▶│ 05 │
//! └──────────┘ └─────┘
//! ┌──────────┐ ┌─────┐
//! │ "ZZ" │ ───────────────▶│ 07 │
//! └──────────┘ └─────┘
//!
//! Example Order Preserving Mapping
//! ```
//! Using the map above, the corresponding row format will be
//!
//! ```text
//! ┌─────┬─────┬─────┬─────┐
//! "Fabulous" │ 01 │ 03 │ 05 │ 00 │
//! └─────┴─────┴─────┴─────┘
//!
//! ┌─────┬─────┬─────┐
//! "ZZ" │ 01 │ 07 │ 00 │
//! └─────┴─────┴─────┘
//!
//! ┌─────┐
//! NULL │ 00 │
//! └─────┘
//!
//! Input Row Format
//! ```
//!
//! ## Struct Encoding
//!
//! A null is encoded as a `0_u8`.
//!
//! A valid value is encoded as `1_u8` followed by the row encoding of each child.
//!
//! This encoding effectively flattens the schema in a depth-first fashion.
//!
//! For example
//!
//! ```text
//! ┌───────┬────────────────────────┬───────┐
//! │ Int32 │ Struct[Int32, Float32] │ Int32 │
//! └───────┴────────────────────────┴───────┘
//! ```
//!
//! Is encoded as
//!
//! ```text
//! ┌───────┬───────────────┬───────┬─────────┬───────┐
//! │ Int32 │ Null Sentinel │ Int32 │ Float32 │ Int32 │
//! └───────┴───────────────┴───────┴─────────┴───────┘
//! ```
//!
//! ## List Encoding
//!
//! Lists are encoded by first encoding all child elements to the row format.
//!
//! A "canonical byte array" is then constructed by concatenating the row
//! encodings of all their elements into a single binary array, followed
//! by the lengths of each encoded row, and the number of elements, encoded
//! as big endian `u32`.
//!
//! This canonical byte array is then encoded using the variable length byte
//! encoding described above.
//!
//! _The lengths are not strictly necessary but greatly simplify decode, they
//! may be removed in a future iteration_.
//!
//! For example given:
//!
//! ```text
//! [1_u8, 2_u8, 3_u8]
//! [1_u8, null]
//! []
//! null
//! ```
//!
//! The elements would be converted to:
//!
//! ```text
//! ┌──┬──┐ ┌──┬──┐ ┌──┬──┐ ┌──┬──┐ ┌──┬──┐
//! 1 │01│01│ 2 │01│02│ 3 │01│03│ 1 │01│01│ null │00│00│
//! └──┴──┘ └──┴──┘ └──┴──┘ └──┴──┘ └──┴──┘
//!```
//!
//! Which would be grouped into the following canonical byte arrays:
//!
//! ```text
//! ┌──┬──┬──┬──┬──┬──┬──┬──┬──┬──┬──┬──┬──┬──┬──┬──┬──┬──┬──┬──┬──┬──┐
//! [1_u8, 2_u8, 3_u8] │01│01│01│02│01│03│00│00│00│02│00│00│00│02│00│00│00│02│00│00│00│03│
//! └──┴──┴──┴──┴──┴──┴──┴──┴──┴──┴──┴──┴──┴──┴──┴──┴──┴──┴──┴──┴──┴──┘
//! └──── rows ────┘ └───────── row lengths ─────────┘ └─ count ─┘
//!
//! ┌──┬──┬──┬──┬──┬──┬──┬──┬──┬──┬──┬──┬──┬──┬──┬──┐
//! [1_u8, null] │01│01│00│00│00│00│00│02│00│00│00│02│00│00│00│02│
//! └──┴──┴──┴──┴──┴──┴──┴──┴──┴──┴──┴──┴──┴──┴──┴──┘
//!```
//!
//! With `[]` represented by an empty byte array, and `null` a null byte array.
//!
//! These byte arrays will then be encoded using the variable length byte encoding
//! described above.
//!
//! # Ordering
//!
//! ## Float Ordering
//!
//! Floats are totally ordered just like in the rest of Polars,
//! -inf < neg < -0.0 = 0.0 < pos < inf < nan, with all nans being equal.
//!
//! ## Null Ordering
//!
//! The encoding described above will order nulls first, this can be inverted by representing
//! nulls as `0xFF_u8` instead of `0_u8`
//!
//! ## Reverse Column Ordering
//!
//! The order of a given column can be reversed by negating the encoded bytes of non-null values
//!
//! [COBS]: https://en.wikipedia.org/wiki/Consistent_Overhead_Byte_Stuffing
//! [byte stuffing]: https://en.wikipedia.org/wiki/High-Level_Data_Link_Control#Asynchronous_framing
extern crate core;
pub mod decode;
pub mod encode;
pub(crate) mod fixed;
mod row;
mod utils;
pub(crate) mod variable;
use arrow::array::*;
pub type ArrayRef = Box<dyn Array>;
pub use encode::{
convert_columns, convert_columns_amortized, convert_columns_amortized_no_order,
convert_columns_no_order,
};
pub use row::{EncodingField, RowsEncoded};