parquet/encodings/

rle.rs

// 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.

//! Rle/Bit-Packing Hybrid Encoding
//! The grammar for this encoding looks like the following (copied verbatim
//! from <https://github.com/Parquet/parquet-format/blob/master/Encodings.md>):
//!
//! rle-bit-packed-hybrid: `<length>` `<encoded-data>`
//! length := length of the `<encoded-data>` in bytes stored as 4 bytes little endian
//! encoded-data := `<run>`*
//! run := `<bit-packed-run>` | `<rle-run>`
//! bit-packed-run := `<bit-packed-header>` `<bit-packed-values>`
//! bit-packed-header := varint-encode(`<bit-pack-count>` << 1 | 1)
//! we always bit-pack a multiple of 8 values at a time, so we only store the number of
//! values / 8
//! bit-pack-count := (number of values in this run) / 8
//! bit-packed-values := *see 1 below*
//! rle-run := `<rle-header>` `<repeated-value>`
//! rle-header := varint-encode( (number of times repeated) << 1)
//! repeated-value := value that is repeated, using a fixed-width of
//! round-up-to-next-byte(bit-width)

use std::{cmp, mem::size_of};

use bytes::Bytes;

use crate::errors::{ParquetError, Result};
use crate::util::bit_util::{self, BitReader, BitWriter, FromBytes};

/// Maximum groups of 8 values per bit-packed run. Current value is 64.
const MAX_GROUPS_PER_BIT_PACKED_RUN: usize = 1 << 6;

/// A RLE/Bit-Packing hybrid encoder.
// TODO: tracking memory usage
pub struct RleEncoder {
    // Number of bits needed to encode the value. Must be in the range of [0, 64].
    bit_width: u8,

    // Underlying writer which holds an internal buffer.
    bit_writer: BitWriter,

    // Buffered values for bit-packed runs.
    buffered_values: [u64; 8],

    // Number of current buffered values. Must be less than 8.
    num_buffered_values: usize,

    // The current (also last) value that was written and the count of how many
    // times in a row that value has been seen.
    current_value: u64,

    // The number of repetitions for `current_value`. If this gets too high we'd
    // switch to use RLE encoding.
    repeat_count: usize,

    // Number of bit-packed values in the current run. This doesn't include values
    // in `buffered_values`.
    bit_packed_count: usize,

    // The position of the indicator byte in the `bit_writer`.
    indicator_byte_pos: i64,
}

impl RleEncoder {
    #[allow(unused)]
    pub fn new(bit_width: u8, buffer_len: usize) -> Self {
        let buffer = Vec::with_capacity(buffer_len);
        RleEncoder::new_from_buf(bit_width, buffer)
    }

    /// Initialize the encoder from existing `buffer`
    pub fn new_from_buf(bit_width: u8, buffer: Vec<u8>) -> Self {
        let bit_writer = BitWriter::new_from_buf(buffer);
        RleEncoder {
            bit_width,
            bit_writer,
            buffered_values: [0; 8],
            num_buffered_values: 0,
            current_value: 0,
            repeat_count: 0,
            bit_packed_count: 0,
            indicator_byte_pos: -1,
        }
    }

    /// Returns the maximum buffer size to encode `num_values` values with
    /// `bit_width`.
    pub fn max_buffer_size(bit_width: u8, num_values: usize) -> usize {
        // The maximum size occurs with the shortest possible runs of 8
        let num_runs = bit_util::ceil(num_values, 8);

        // The number of bytes in a run of 8
        let bytes_per_run = bit_width as usize;

        // The maximum size if stored as shortest possible bit packed runs of 8
        let bit_packed_max_size = num_runs + num_runs * bytes_per_run;

        // The length of `8` VLQ encoded
        let rle_len_prefix = 1;

        // The length of an RLE run of 8
        let min_rle_run_size = rle_len_prefix + bit_util::ceil(bit_width as usize, 8);

        // The maximum size if stored as shortest possible RLE runs of 8
        let rle_max_size = num_runs * min_rle_run_size;

        bit_packed_max_size.max(rle_max_size)
    }

    /// Encodes `value`, which must be representable with `bit_width` bits.
    #[inline]
    pub fn put(&mut self, value: u64) {
        // This function buffers 8 values at a time. After seeing 8 values, it
        // decides whether the current run should be encoded in bit-packed or RLE.
        if self.current_value == value {
            self.repeat_count += 1;
            if self.repeat_count > 8 {
                // A continuation of last value. No need to buffer.
                return;
            }
        } else {
            if self.repeat_count >= 8 {
                // The current RLE run has ended and we've gathered enough. Flush first.
                assert_eq!(self.bit_packed_count, 0);
                self.flush_rle_run();
            }
            self.repeat_count = 1;
            self.current_value = value;
        }

        self.buffered_values[self.num_buffered_values] = value;
        self.num_buffered_values += 1;
        if self.num_buffered_values == 8 {
            // Buffered values are full. Flush them.
            assert_eq!(self.bit_packed_count % 8, 0);
            self.flush_buffered_values();
        }
    }

    #[inline]
    #[allow(unused)]
    pub fn buffer(&self) -> &[u8] {
        self.bit_writer.buffer()
    }

    #[inline]
    pub fn len(&self) -> usize {
        self.bit_writer.bytes_written()
    }

    #[allow(unused)]
    pub fn is_empty(&self) -> bool {
        self.bit_writer.bytes_written() == 0
    }

    #[inline]
    pub fn consume(mut self) -> Vec<u8> {
        self.flush();
        self.bit_writer.consume()
    }

    /// Borrow equivalent of the `consume` method.
    /// Call `clear()` after invoking this method.
    #[inline]
    #[allow(unused)]
    pub fn flush_buffer(&mut self) -> &[u8] {
        self.flush();
        self.bit_writer.flush_buffer()
    }

    /// Clears the internal state so this encoder can be reused (e.g., after becoming
    /// full).
    #[inline]
    #[allow(unused)]
    pub fn clear(&mut self) {
        self.bit_writer.clear();
        self.num_buffered_values = 0;
        self.current_value = 0;
        self.repeat_count = 0;
        self.bit_packed_count = 0;
        self.indicator_byte_pos = -1;
    }

    /// Flushes all remaining values and return the final byte buffer maintained by the
    /// internal writer.
    #[inline]
    pub fn flush(&mut self) {
        if self.bit_packed_count > 0 || self.repeat_count > 0 || self.num_buffered_values > 0 {
            let all_repeat = self.bit_packed_count == 0
                && (self.repeat_count == self.num_buffered_values || self.num_buffered_values == 0);
            if self.repeat_count > 0 && all_repeat {
                self.flush_rle_run();
            } else {
                // Buffer the last group of bit-packed values to 8 by padding with 0s.
                if self.num_buffered_values > 0 {
                    while self.num_buffered_values < 8 {
                        self.buffered_values[self.num_buffered_values] = 0;
                        self.num_buffered_values += 1;
                    }
                }
                self.bit_packed_count += self.num_buffered_values;
                self.flush_bit_packed_run(true);
                self.repeat_count = 0;
            }
        }
    }

    fn flush_rle_run(&mut self) {
        assert!(self.repeat_count > 0);
        let indicator_value = self.repeat_count << 1;
        self.bit_writer.put_vlq_int(indicator_value as u64);
        self.bit_writer.put_aligned(
            self.current_value,
            bit_util::ceil(self.bit_width as usize, 8),
        );
        self.num_buffered_values = 0;
        self.repeat_count = 0;
    }

    fn flush_bit_packed_run(&mut self, update_indicator_byte: bool) {
        if self.indicator_byte_pos < 0 {
            self.indicator_byte_pos = self.bit_writer.skip(1) as i64;
        }

        // Write all buffered values as bit-packed literals
        for i in 0..self.num_buffered_values {
            self.bit_writer
                .put_value(self.buffered_values[i], self.bit_width as usize);
        }
        self.num_buffered_values = 0;
        if update_indicator_byte {
            // Write the indicator byte to the reserved position in `bit_writer`
            let num_groups = self.bit_packed_count / 8;
            let indicator_byte = ((num_groups << 1) | 1) as u8;
            self.bit_writer
                .put_aligned_offset(indicator_byte, 1, self.indicator_byte_pos as usize);
            self.indicator_byte_pos = -1;
            self.bit_packed_count = 0;
        }
    }

    #[inline(never)]
    fn flush_buffered_values(&mut self) {
        if self.repeat_count >= 8 {
            self.num_buffered_values = 0;
            if self.bit_packed_count > 0 {
                // In this case we choose RLE encoding. Flush the current buffered values
                // as bit-packed encoding.
                assert_eq!(self.bit_packed_count % 8, 0);
                self.flush_bit_packed_run(true)
            }
            return;
        }

        self.bit_packed_count += self.num_buffered_values;
        let num_groups = self.bit_packed_count / 8;
        if num_groups + 1 >= MAX_GROUPS_PER_BIT_PACKED_RUN {
            // We've reached the maximum value that can be hold in a single bit-packed
            // run.
            assert!(self.indicator_byte_pos >= 0);
            self.flush_bit_packed_run(true);
        } else {
            self.flush_bit_packed_run(false);
        }
        self.repeat_count = 0;
    }

    /// return the estimated memory size of this encoder.
    pub(crate) fn estimated_memory_size(&self) -> usize {
        self.bit_writer.estimated_memory_size() + std::mem::size_of::<Self>()
    }
}

/// Size, in number of `i32s` of buffer to use for RLE batch reading
const RLE_DECODER_INDEX_BUFFER_SIZE: usize = 1024;

/// A RLE/Bit-Packing hybrid decoder.
pub struct RleDecoder {
    // Number of bits used to encode the value. Must be between [0, 64].
    bit_width: u8,

    // Bit reader loaded with input buffer.
    bit_reader: Option<BitReader>,

    // Buffer used when `bit_reader` is not `None`, for batch reading.
    index_buf: Option<Box<[i32; RLE_DECODER_INDEX_BUFFER_SIZE]>>,

    // The remaining number of values in RLE for this run
    rle_left: u32,

    // The remaining number of values in Bit-Packing for this run
    bit_packed_left: u32,

    // The current value for the case of RLE mode
    current_value: Option<u64>,
}

impl RleDecoder {
    pub fn new(bit_width: u8) -> Self {
        RleDecoder {
            bit_width,
            rle_left: 0,
            bit_packed_left: 0,
            bit_reader: None,
            index_buf: None,
            current_value: None,
        }
    }

    #[inline]
    pub fn set_data(&mut self, data: Bytes) {
        if let Some(ref mut bit_reader) = self.bit_reader {
            bit_reader.reset(data);
        } else {
            self.bit_reader = Some(BitReader::new(data));
        }

        let _ = self.reload();
    }

    // These functions inline badly, they tend to inline and then create very large loop unrolls
    // that damage L1d-cache occupancy. This results in a ~18% performance drop
    #[inline(never)]
    #[allow(unused)]
    pub fn get<T: FromBytes>(&mut self) -> Result<Option<T>> {
        assert!(size_of::<T>() <= 8);

        while self.rle_left == 0 && self.bit_packed_left == 0 {
            if !self.reload() {
                return Ok(None);
            }
        }

        let value = if self.rle_left > 0 {
            let rle_value = T::try_from_le_slice(
                &self
                    .current_value
                    .as_mut()
                    .expect("current_value should be Some")
                    .to_ne_bytes(),
            )?;
            self.rle_left -= 1;
            rle_value
        } else {
            // self.bit_packed_left > 0
            let bit_reader = self.bit_reader.as_mut().expect("bit_reader should be Some");
            let bit_packed_value = bit_reader
                .get_value(self.bit_width as usize)
                .ok_or_else(|| eof_err!("Not enough data for 'bit_packed_value'"))?;
            self.bit_packed_left -= 1;
            bit_packed_value
        };

        Ok(Some(value))
    }

    #[inline(never)]
    pub fn get_batch<T: FromBytes + Clone>(&mut self, buffer: &mut [T]) -> Result<usize> {
        assert!(size_of::<T>() <= 8);

        let mut values_read = 0;
        while values_read < buffer.len() {
            if self.rle_left > 0 {
                let num_values = cmp::min(buffer.len() - values_read, self.rle_left as usize);
                let repeated_value =
                    T::try_from_le_slice(&self.current_value.as_mut().unwrap().to_ne_bytes())?;
                buffer[values_read..values_read + num_values].fill(repeated_value);
                self.rle_left -= num_values as u32;
                values_read += num_values;
            } else if self.bit_packed_left > 0 {
                let mut num_values =
                    cmp::min(buffer.len() - values_read, self.bit_packed_left as usize);
                let bit_reader = self.bit_reader.as_mut().expect("bit_reader should be set");

                num_values = bit_reader.get_batch::<T>(
                    &mut buffer[values_read..values_read + num_values],
                    self.bit_width as usize,
                );
                if num_values == 0 {
                    // Handle writers which truncate the final block
                    self.bit_packed_left = 0;
                    continue;
                }
                self.bit_packed_left -= num_values as u32;
                values_read += num_values;
            } else if !self.reload() {
                break;
            }
        }

        Ok(values_read)
    }

    #[inline(never)]
    pub fn skip(&mut self, num_values: usize) -> Result<usize> {
        let mut values_skipped = 0;
        while values_skipped < num_values {
            if self.rle_left > 0 {
                let num_values = cmp::min(num_values - values_skipped, self.rle_left as usize);
                self.rle_left -= num_values as u32;
                values_skipped += num_values;
            } else if self.bit_packed_left > 0 {
                let mut num_values =
                    cmp::min(num_values - values_skipped, self.bit_packed_left as usize);
                let bit_reader = self.bit_reader.as_mut().expect("bit_reader should be set");

                num_values = bit_reader.skip(num_values, self.bit_width as usize);
                if num_values == 0 {
                    // Handle writers which truncate the final block
                    self.bit_packed_left = 0;
                    continue;
                }
                self.bit_packed_left -= num_values as u32;
                values_skipped += num_values;
            } else if !self.reload() {
                break;
            }
        }

        Ok(values_skipped)
    }

    #[inline(never)]
    pub fn get_batch_with_dict<T>(
        &mut self,
        dict: &[T],
        buffer: &mut [T],
        max_values: usize,
    ) -> Result<usize>
    where
        T: Default + Clone,
    {
        assert!(buffer.len() >= max_values);

        let mut values_read = 0;
        while values_read < max_values {
            let index_buf = self.index_buf.get_or_insert_with(|| Box::new([0; 1024]));

            if self.rle_left > 0 {
                let num_values = cmp::min(max_values - values_read, self.rle_left as usize);
                let dict_idx = self.current_value.unwrap() as usize;
                let dict_value = dict[dict_idx].clone();

                buffer[values_read..values_read + num_values].fill(dict_value);

                self.rle_left -= num_values as u32;
                values_read += num_values;
            } else if self.bit_packed_left > 0 {
                let bit_reader = self.bit_reader.as_mut().expect("bit_reader should be set");

                loop {
                    let to_read = index_buf
                        .len()
                        .min(max_values - values_read)
                        .min(self.bit_packed_left as usize);

                    if to_read == 0 {
                        break;
                    }

                    let num_values = bit_reader
                        .get_batch::<i32>(&mut index_buf[..to_read], self.bit_width as usize);
                    if num_values == 0 {
                        // Handle writers which truncate the final block
                        self.bit_packed_left = 0;
                        break;
                    }
                    buffer[values_read..values_read + num_values]
                        .iter_mut()
                        .zip(index_buf[..num_values].iter())
                        .for_each(|(b, i)| b.clone_from(&dict[*i as usize]));
                    self.bit_packed_left -= num_values as u32;
                    values_read += num_values;
                    if num_values < to_read {
                        break;
                    }
                }
            } else if !self.reload() {
                break;
            }
        }

        Ok(values_read)
    }

    #[inline]
    fn reload(&mut self) -> bool {
        let bit_reader = self.bit_reader.as_mut().expect("bit_reader should be set");

        if let Some(indicator_value) = bit_reader.get_vlq_int() {
            // fastparquet adds padding to the end of pages. This is not spec-compliant
            // but is handled by the C++ implementation
            // <https://github.com/apache/arrow/blob/8074496cb41bc8ec8fe9fc814ca5576d89a6eb94/cpp/src/arrow/util/rle_encoding.h#L653>
            if indicator_value == 0 {
                return false;
            }
            if indicator_value & 1 == 1 {
                self.bit_packed_left = ((indicator_value >> 1) * 8) as u32;
            } else {
                self.rle_left = (indicator_value >> 1) as u32;
                let value_width = bit_util::ceil(self.bit_width as usize, 8);
                self.current_value = bit_reader.get_aligned::<u64>(value_width);
                assert!(self.current_value.is_some());
            }
            true
        } else {
            false
        }
    }
}

#[cfg(test)]
mod tests {
    use super::*;

    use crate::util::bit_util::ceil;
    use rand::{self, distributions::Standard, thread_rng, Rng, SeedableRng};

    const MAX_WIDTH: usize = 32;

    #[test]
    fn test_rle_decode_int32() {
        // Test data: 0-7 with bit width 3
        // 00000011 10001000 11000110 11111010
        let data = vec![0x03, 0x88, 0xC6, 0xFA];
        let mut decoder: RleDecoder = RleDecoder::new(3);
        decoder.set_data(data.into());
        let mut buffer = vec![0; 8];
        let expected = vec![0, 1, 2, 3, 4, 5, 6, 7];
        let result = decoder.get_batch::<i32>(&mut buffer);
        assert!(result.is_ok());
        assert_eq!(buffer, expected);
    }

    #[test]
    fn test_rle_skip_int32() {
        // Test data: 0-7 with bit width 3
        // 00000011 10001000 11000110 11111010
        let data = vec![0x03, 0x88, 0xC6, 0xFA];
        let mut decoder: RleDecoder = RleDecoder::new(3);
        decoder.set_data(data.into());
        let expected = vec![2, 3, 4, 5, 6, 7];
        let skipped = decoder.skip(2).expect("skipping values");
        assert_eq!(skipped, 2);

        let mut buffer = vec![0; 6];
        let remaining = decoder
            .get_batch::<i32>(&mut buffer)
            .expect("getting remaining");
        assert_eq!(remaining, 6);
        assert_eq!(buffer, expected);
    }

    #[test]
    fn test_rle_consume_flush_buffer() {
        let data = vec![1, 1, 1, 2, 2, 3, 3, 3];
        let mut encoder1 = RleEncoder::new(3, 256);
        let mut encoder2 = RleEncoder::new(3, 256);
        for value in data {
            encoder1.put(value as u64);
            encoder2.put(value as u64);
        }
        let res1 = encoder1.flush_buffer();
        let res2 = encoder2.consume();
        assert_eq!(res1, &res2[..]);
    }

    #[test]
    fn test_rle_decode_bool() {
        // RLE test data: 50 1s followed by 50 0s
        // 01100100 00000001 01100100 00000000
        let data1 = vec![0x64, 0x01, 0x64, 0x00];

        // Bit-packing test data: alternating 1s and 0s, 100 total
        // 100 / 8 = 13 groups
        // 00011011 10101010 ... 00001010
        let data2 = vec![
            0x1B, 0xAA, 0xAA, 0xAA, 0xAA, 0xAA, 0xAA, 0xAA, 0xAA, 0xAA, 0xAA, 0xAA, 0xAA, 0x0A,
        ];

        let mut decoder: RleDecoder = RleDecoder::new(1);
        decoder.set_data(data1.into());
        let mut buffer = vec![false; 100];
        let mut expected = vec![];
        for i in 0..100 {
            if i < 50 {
                expected.push(true);
            } else {
                expected.push(false);
            }
        }
        let result = decoder.get_batch::<bool>(&mut buffer);
        assert!(result.is_ok());
        assert_eq!(buffer, expected);

        decoder.set_data(data2.into());
        let mut buffer = vec![false; 100];
        let mut expected = vec![];
        for i in 0..100 {
            if i % 2 == 0 {
                expected.push(false);
            } else {
                expected.push(true);
            }
        }
        let result = decoder.get_batch::<bool>(&mut buffer);
        assert!(result.is_ok());
        assert_eq!(buffer, expected);
    }

    #[test]
    fn test_rle_skip_bool() {
        // RLE test data: 50 1s followed by 50 0s
        // 01100100 00000001 01100100 00000000
        let data1 = vec![0x64, 0x01, 0x64, 0x00];

        // Bit-packing test data: alternating 1s and 0s, 100 total
        // 100 / 8 = 13 groups
        // 00011011 10101010 ... 00001010
        let data2 = vec![
            0x1B, 0xAA, 0xAA, 0xAA, 0xAA, 0xAA, 0xAA, 0xAA, 0xAA, 0xAA, 0xAA, 0xAA, 0xAA, 0x0A,
        ];

        let mut decoder: RleDecoder = RleDecoder::new(1);
        decoder.set_data(data1.into());
        let mut buffer = vec![true; 50];
        let expected = vec![false; 50];

        let skipped = decoder.skip(50).expect("skipping first 50");
        assert_eq!(skipped, 50);
        let remainder = decoder
            .get_batch::<bool>(&mut buffer)
            .expect("getting remaining 50");
        assert_eq!(remainder, 50);
        assert_eq!(buffer, expected);

        decoder.set_data(data2.into());
        let mut buffer = vec![false; 50];
        let mut expected = vec![];
        for i in 0..50 {
            if i % 2 == 0 {
                expected.push(false);
            } else {
                expected.push(true);
            }
        }
        let skipped = decoder.skip(50).expect("skipping first 50");
        assert_eq!(skipped, 50);
        let remainder = decoder
            .get_batch::<bool>(&mut buffer)
            .expect("getting remaining 50");
        assert_eq!(remainder, 50);
        assert_eq!(buffer, expected);
    }

    #[test]
    fn test_rle_decode_with_dict_int32() {
        // Test RLE encoding: 3 0s followed by 4 1s followed by 5 2s
        // 00000110 00000000 00001000 00000001 00001010 00000010
        let dict = vec![10, 20, 30];
        let data = vec![0x06, 0x00, 0x08, 0x01, 0x0A, 0x02];
        let mut decoder: RleDecoder = RleDecoder::new(3);
        decoder.set_data(data.into());
        let mut buffer = vec![0; 12];
        let expected = vec![10, 10, 10, 20, 20, 20, 20, 30, 30, 30, 30, 30];
        let result = decoder.get_batch_with_dict::<i32>(&dict, &mut buffer, 12);
        assert!(result.is_ok());
        assert_eq!(buffer, expected);

        // Test bit-pack encoding: 345345345455 (2 groups: 8 and 4)
        // 011 100 101 011 100 101 011 100 101 100 101 101
        // 00000011 01100011 11000111 10001110 00000011 01100101 00001011
        let dict = vec!["aaa", "bbb", "ccc", "ddd", "eee", "fff"];
        let data = vec![0x03, 0x63, 0xC7, 0x8E, 0x03, 0x65, 0x0B];
        let mut decoder: RleDecoder = RleDecoder::new(3);
        decoder.set_data(data.into());
        let mut buffer = vec![""; 12];
        let expected = vec![
            "ddd", "eee", "fff", "ddd", "eee", "fff", "ddd", "eee", "fff", "eee", "fff", "fff",
        ];
        let result =
            decoder.get_batch_with_dict::<&str>(dict.as_slice(), buffer.as_mut_slice(), 12);
        assert!(result.is_ok());
        assert_eq!(buffer, expected);
    }

    #[test]
    fn test_rle_skip_dict() {
        // Test RLE encoding: 3 0s followed by 4 1s followed by 5 2s
        // 00000110 00000000 00001000 00000001 00001010 00000010
        let dict = vec![10, 20, 30];
        let data = vec![0x06, 0x00, 0x08, 0x01, 0x0A, 0x02];
        let mut decoder: RleDecoder = RleDecoder::new(3);
        decoder.set_data(data.into());
        let mut buffer = vec![0; 10];
        let expected = vec![10, 20, 20, 20, 20, 30, 30, 30, 30, 30];
        let skipped = decoder.skip(2).expect("skipping two values");
        assert_eq!(skipped, 2);
        let remainder = decoder
            .get_batch_with_dict::<i32>(&dict, &mut buffer, 10)
            .expect("getting remainder");
        assert_eq!(remainder, 10);
        assert_eq!(buffer, expected);

        // Test bit-pack encoding: 345345345455 (2 groups: 8 and 4)
        // 011 100 101 011 100 101 011 100 101 100 101 101
        // 00000011 01100011 11000111 10001110 00000011 01100101 00001011
        let dict = vec!["aaa", "bbb", "ccc", "ddd", "eee", "fff"];
        let data = vec![0x03, 0x63, 0xC7, 0x8E, 0x03, 0x65, 0x0B];
        let mut decoder: RleDecoder = RleDecoder::new(3);
        decoder.set_data(data.into());
        let mut buffer = vec![""; 8];
        let expected = vec!["eee", "fff", "ddd", "eee", "fff", "eee", "fff", "fff"];
        let skipped = decoder.skip(4).expect("skipping four values");
        assert_eq!(skipped, 4);
        let remainder = decoder
            .get_batch_with_dict::<&str>(dict.as_slice(), buffer.as_mut_slice(), 8)
            .expect("getting remainder");
        assert_eq!(remainder, 8);
        assert_eq!(buffer, expected);
    }

    fn validate_rle(
        values: &[i64],
        bit_width: u8,
        expected_encoding: Option<&[u8]>,
        expected_len: i32,
    ) {
        let buffer_len = 64 * 1024;
        let mut encoder = RleEncoder::new(bit_width, buffer_len);
        for v in values {
            encoder.put(*v as u64)
        }
        let buffer: Bytes = encoder.consume().into();
        if expected_len != -1 {
            assert_eq!(buffer.len(), expected_len as usize);
        }
        if let Some(b) = expected_encoding {
            assert_eq!(buffer.as_ref(), b);
        }

        // Verify read
        let mut decoder = RleDecoder::new(bit_width);
        decoder.set_data(buffer.clone());
        for v in values {
            let val: i64 = decoder
                .get()
                .expect("get() should be OK")
                .expect("get() should return more value");
            assert_eq!(val, *v);
        }

        // Verify batch read
        decoder.set_data(buffer);
        let mut values_read: Vec<i64> = vec![0; values.len()];
        decoder
            .get_batch(&mut values_read[..])
            .expect("get_batch() should be OK");
        assert_eq!(&values_read[..], values);
    }

    #[test]
    fn test_rle_specific_sequences() {
        let mut expected_buffer = Vec::new();
        let mut values = vec![0; 50];
        values.resize(100, 1);

        expected_buffer.push(50 << 1);
        expected_buffer.push(0);
        expected_buffer.push(50 << 1);
        expected_buffer.push(1);

        for width in 1..9 {
            validate_rle(&values[..], width, Some(&expected_buffer[..]), 4);
        }
        for width in 9..MAX_WIDTH + 1 {
            validate_rle(
                &values[..],
                width as u8,
                None,
                2 * (1 + bit_util::ceil(width as i64, 8) as i32),
            );
        }

        // Test 100 0's and 1's alternating
        values.clear();
        expected_buffer.clear();
        for i in 0..101 {
            values.push(i % 2);
        }
        let num_groups = bit_util::ceil(100, 8) as u8;
        expected_buffer.push((num_groups << 1) | 1);
        expected_buffer.resize(expected_buffer.len() + 100 / 8, 0b10101010);

        // For the last 4 0 and 1's, padded with 0.
        expected_buffer.push(0b00001010);
        validate_rle(
            &values,
            1,
            Some(&expected_buffer[..]),
            1 + num_groups as i32,
        );
        for width in 2..MAX_WIDTH + 1 {
            let num_values = bit_util::ceil(100, 8) * 8;
            validate_rle(
                &values,
                width as u8,
                None,
                1 + bit_util::ceil(width as i64 * num_values, 8) as i32,
            );
        }
    }

    // `validate_rle` on `num_vals` with width `bit_width`. If `value` is -1, that value
    // is used, otherwise alternating values are used.
    fn test_rle_values(bit_width: usize, num_vals: usize, value: i32) {
        let mod_val = if bit_width == 64 {
            1
        } else {
            1u64 << bit_width
        };
        let mut values: Vec<i64> = vec![];
        for v in 0..num_vals {
            let val = if value == -1 {
                v as i64 % mod_val as i64
            } else {
                value as i64
            };
            values.push(val);
        }
        validate_rle(&values, bit_width as u8, None, -1);
    }

    #[test]
    fn test_values() {
        for width in 1..MAX_WIDTH + 1 {
            test_rle_values(width, 1, -1);
            test_rle_values(width, 1024, -1);
            test_rle_values(width, 1024, 0);
            test_rle_values(width, 1024, 1);
        }
    }

    #[test]
    fn test_truncated_rle() {
        // The final bit packed run within a page may not be a multiple of 8 values
        // Unfortunately the specification stores `(bit-packed-run-len) / 8`
        // This means we don't necessarily know how many values are present
        // and some writers may not add padding to compensate for this ambiguity

        // Bit pack encode 20 values with a bit width of 8
        let mut data: Vec<u8> = vec![
            (3 << 1) | 1, // bit-packed run of 3 * 8
        ];
        data.extend(std::iter::repeat(0xFF).take(20));
        let data: Bytes = data.into();

        let mut decoder = RleDecoder::new(8);
        decoder.set_data(data.clone());

        let mut output = vec![0_u16; 100];
        let read = decoder.get_batch(&mut output).unwrap();

        assert_eq!(read, 20);
        assert!(output.iter().take(20).all(|x| *x == 255));

        // Reset decoder
        decoder.set_data(data);

        let dict: Vec<u16> = (0..256).collect();
        let mut output = vec![0_u16; 100];
        let read = decoder
            .get_batch_with_dict(&dict, &mut output, 100)
            .unwrap();

        assert_eq!(read, 20);
        assert!(output.iter().take(20).all(|x| *x == 255));
    }

    #[test]
    fn test_rle_padded() {
        let values: Vec<i16> = vec![0, 1, 1, 3, 1, 0];
        let bit_width = 2;
        let buffer_len = RleEncoder::max_buffer_size(bit_width, values.len());
        let mut encoder = RleEncoder::new(bit_width, buffer_len + 1);
        for v in &values {
            encoder.put(*v as u64)
        }

        let mut buffer = encoder.consume();
        buffer.push(0);

        let mut decoder = RleDecoder::new(bit_width);
        decoder.set_data(buffer.into());

        // We don't always reliably know how many non-null values are contained in a page
        // and so the decoder must work correctly without a precise value count
        let mut actual_values: Vec<i16> = vec![0; 12];
        let r = decoder
            .get_batch(&mut actual_values)
            .expect("get_batch() should be OK");

        // Should decode 8 values despite only encoding 6 as length of
        // bit packed run is always multiple of 8
        assert_eq!(r, 8);
        assert_eq!(actual_values[..6], values);
        assert_eq!(actual_values[6], 0);
        assert_eq!(actual_values[7], 0);
    }

    #[test]
    fn test_long_run() {
        // This writer does not write runs longer than 504 values as this allows
        // encoding the run header as a single byte
        //
        // This tests that the decoder correctly handles longer runs

        let mut writer = BitWriter::new(1024);
        let bit_width = 1;

        // Choose a non-multiple of 8 larger than 1024 so that the length
        // of the run is ambiguous, as the encoding only stores `num_values / 8`
        let num_values = 2002;

        // bit-packed header
        let run_bytes = ceil(num_values * bit_width, 8) as u64;
        writer.put_vlq_int((run_bytes << 1) | 1);
        for _ in 0..run_bytes {
            writer.put_aligned(0xFF_u8, 1);
        }
        let buffer: Bytes = writer.consume().into();

        let mut decoder = RleDecoder::new(1);
        decoder.set_data(buffer.clone());

        let mut decoded: Vec<i16> = vec![0; num_values];
        let r = decoder.get_batch(&mut decoded).unwrap();
        assert_eq!(r, num_values);
        assert_eq!(vec![1; num_values], decoded);

        decoder.set_data(buffer);
        let r = decoder
            .get_batch_with_dict(&[0, 23], &mut decoded, num_values)
            .unwrap();
        assert_eq!(r, num_values);
        assert_eq!(vec![23; num_values], decoded);
    }

    #[test]
    fn test_rle_specific_roundtrip() {
        let bit_width = 1;
        let values: Vec<i16> = vec![0, 1, 1, 1, 1, 0, 0, 0, 0, 1];
        let buffer_len = RleEncoder::max_buffer_size(bit_width, values.len());
        let mut encoder = RleEncoder::new(bit_width, buffer_len);
        for v in &values {
            encoder.put(*v as u64)
        }
        let buffer = encoder.consume();
        let mut decoder = RleDecoder::new(bit_width);
        decoder.set_data(Bytes::from(buffer));
        let mut actual_values: Vec<i16> = vec![0; values.len()];
        decoder
            .get_batch(&mut actual_values)
            .expect("get_batch() should be OK");
        assert_eq!(actual_values, values);
    }

    fn test_round_trip(values: &[i32], bit_width: u8) {
        let buffer_len = 64 * 1024;
        let mut encoder = RleEncoder::new(bit_width, buffer_len);
        for v in values {
            encoder.put(*v as u64)
        }

        let buffer = Bytes::from(encoder.consume());

        // Verify read
        let mut decoder = RleDecoder::new(bit_width);
        decoder.set_data(buffer.clone());
        for v in values {
            let val = decoder
                .get::<i32>()
                .expect("get() should be OK")
                .expect("get() should return value");
            assert_eq!(val, *v);
        }

        // Verify batch read
        let mut decoder = RleDecoder::new(bit_width);
        decoder.set_data(buffer);
        let mut values_read: Vec<i32> = vec![0; values.len()];
        decoder
            .get_batch(&mut values_read[..])
            .expect("get_batch() should be OK");
        assert_eq!(&values_read[..], values);
    }

    #[test]
    fn test_random() {
        let seed_len = 32;
        let niters = 50;
        let ngroups = 1000;
        let max_group_size = 15;
        let mut values = vec![];

        for _ in 0..niters {
            values.clear();
            let rng = thread_rng();
            let seed_vec: Vec<u8> = rng.sample_iter::<u8, _>(&Standard).take(seed_len).collect();
            let mut seed = [0u8; 32];
            seed.copy_from_slice(&seed_vec[0..seed_len]);
            let mut gen = rand::rngs::StdRng::from_seed(seed);

            let mut parity = false;
            for _ in 0..ngroups {
                let mut group_size = gen.gen_range(1..20);
                if group_size > max_group_size {
                    group_size = 1;
                }
                for _ in 0..group_size {
                    values.push(parity as i32);
                }
                parity = !parity;
            }
            let bit_width = bit_util::num_required_bits(values.len() as u64);
            assert!(bit_width < 64);
            test_round_trip(&values[..], bit_width);
        }
    }
}