strawboat 0.2.6

// Licensed to the Apache Software Foundation (ASF) under one
// or more contributor license agreements.  See the NOTICE file
// distributed with this work for additional information
// regarding copyright ownership.  The ASF licenses this file
// to you under the Apache License, Version 2.0 (the
// "License"); you may not use this file except in compliance
// with the License.  You may obtain a copy of the License at
//
//   http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing,
// software distributed under the License is distributed on an
// "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
// KIND, either express or implied.  See the License for the
// specific language governing permissions and limitations
// under the License.

use std::io::{Read, Write};

use arrow::array::PrimitiveArray;
use arrow::bitmap::Bitmap;

use arrow::error::Result;
use byteorder::{LittleEndian, ReadBytesExt};

use crate::{
    compression::{integer::RLE, is_valid, Compression, SAMPLE_COUNT, SAMPLE_SIZE},
    write::WriteOptions,
};

use super::{compress_sample_ratio, DoubleCompression, DoubleStats, DoubleType};

impl<T: DoubleType> DoubleCompression<T> for RLE {
    fn compress(
        &self,
        array: &PrimitiveArray<T>,
        _stats: &DoubleStats<T>,
        _write_options: &WriteOptions,
        output: &mut Vec<u8>,
    ) -> Result<usize> {
        let size = output.len();
        self.compress_double(output, array.values().clone(), array.validity())?;
        Ok(output.len() - size)
    }

    fn decompress(&self, input: &[u8], length: usize, output: &mut Vec<T>) -> Result<()> {
        let _ = self.decompress_double(input, length, output)?;
        Ok(())
    }

    fn to_compression(&self) -> Compression {
        Compression::Rle
    }

    fn compress_ratio(&self, stats: &DoubleStats<T>) -> f64 {
        #[cfg(debug_assertions)]
        {
            if option_env!("STRAWBOAT_RLE_COMPRESSION") == Some("1") {
                return f64::MAX;
            }
        }

        compress_sample_ratio(self, stats, SAMPLE_COUNT, SAMPLE_SIZE)
    }
}

impl RLE {
    pub fn compress_double<T: DoubleType, W: Write>(
        &self,
        w: &mut W,
        values: impl IntoIterator<Item = T>,
        validity: Option<&Bitmap>,
    ) -> Result<()> {
        // help me generate RLE encode algorithm
        let mut seen_count: u32 = 0;
        let mut last_value = T::default().as_order();
        let mut all_null = true;

        for (i, item) in values.into_iter().enumerate() {
            let item = item.as_order();

            if is_valid(&validity, i) {
                if all_null {
                    all_null = false;
                    last_value = item;

                    seen_count += 1;
                } else if last_value != item {
                    // flush  u32 cnt , value
                    w.write_all(&seen_count.to_le_bytes())?;
                    w.write_all(T::from_order(last_value).to_le_bytes().as_ref())?;

                    last_value = item;
                    seen_count = 1;
                } else {
                    seen_count += 1;
                }
            } else {
                // NULL value: we merely increment the seen_count
                seen_count += 1;
            }
        }

        if seen_count != 0 {
            w.write_all(&seen_count.to_le_bytes())?;
            w.write_all(T::from_order(last_value).to_le_bytes().as_ref())?;
        }

        Ok(())
    }

    pub fn decompress_double<'a, T: DoubleType>(
        &self,
        mut input: &'a [u8],
        length: usize,
        array: &mut Vec<T>,
    ) -> Result<&'a [u8]> {
        let mut bs = vec![0u8; std::mem::size_of::<T>()];
        let mut num_values = 0;

        array.reserve(length);

        loop {
            let len = input.read_u32::<LittleEndian>()?;
            input.read_exact(&mut bs)?;

            let a: T::Bytes = match bs.as_slice().try_into() {
                Ok(a) => a,
                Err(_) => unreachable!(),
            };
            let t = T::from_le_bytes(a);
            for _ in 0..len {
                array.push(t);
            }

            num_values += len as usize;
            if num_values >= length {
                break;
            }
        }
        Ok(input)
    }
}