parquet/util/

bit_util.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.

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

use bytes::Bytes;

use crate::data_type::{AsBytes, ByteArray, FixedLenByteArray, Int96};
use crate::errors::{ParquetError, Result};
use crate::util::bit_pack::{unpack16, unpack32, unpack64, unpack8};

#[inline]
fn array_from_slice<const N: usize>(bs: &[u8]) -> Result<[u8; N]> {
    // Need to slice as may be called with zero-padded values
    match bs.get(..N) {
        Some(b) => Ok(b.try_into().unwrap()),
        None => Err(general_err!(
            "error converting value, expected {} bytes got {}",
            N,
            bs.len()
        )),
    }
}

/// # Safety
/// All bit patterns 00000xxxx, where there are `BIT_CAPACITY` `x`s,
/// must be valid, unless BIT_CAPACITY is 0.
pub unsafe trait FromBytes: Sized {
    const BIT_CAPACITY: usize;
    type Buffer: AsMut<[u8]> + Default;
    fn try_from_le_slice(b: &[u8]) -> Result<Self>;
    fn from_le_bytes(bs: Self::Buffer) -> Self;
}

macro_rules! from_le_bytes {
    ($($ty: ty),*) => {
        $(
        // SAFETY: this macro is used for types for which all bit patterns are valid.
        unsafe impl FromBytes for $ty {
            const BIT_CAPACITY: usize = std::mem::size_of::<$ty>() * 8;
            type Buffer = [u8; size_of::<Self>()];
            fn try_from_le_slice(b: &[u8]) -> Result<Self> {
                Ok(Self::from_le_bytes(array_from_slice(b)?))
            }
            fn from_le_bytes(bs: Self::Buffer) -> Self {
                <$ty>::from_le_bytes(bs)
            }
        }
        )*
    };
}

from_le_bytes! { u8, u16, u32, u64, i8, i16, i32, i64, f32, f64 }

// SAFETY: the 0000000x bit pattern is always valid for `bool`.
unsafe impl FromBytes for bool {
    const BIT_CAPACITY: usize = 1;
    type Buffer = [u8; 1];

    fn try_from_le_slice(b: &[u8]) -> Result<Self> {
        Ok(Self::from_le_bytes(array_from_slice(b)?))
    }
    fn from_le_bytes(bs: Self::Buffer) -> Self {
        bs[0] != 0
    }
}

// SAFETY: BIT_CAPACITY is 0.
unsafe impl FromBytes for Int96 {
    const BIT_CAPACITY: usize = 0;
    type Buffer = [u8; 12];

    fn try_from_le_slice(b: &[u8]) -> Result<Self> {
        let bs: [u8; 12] = array_from_slice(b)?;
        let mut i = Int96::new();
        i.set_data(
            u32::try_from_le_slice(&bs[0..4])?,
            u32::try_from_le_slice(&bs[4..8])?,
            u32::try_from_le_slice(&bs[8..12])?,
        );
        Ok(i)
    }

    fn from_le_bytes(bs: Self::Buffer) -> Self {
        let mut i = Int96::new();
        i.set_data(
            u32::try_from_le_slice(&bs[0..4]).unwrap(),
            u32::try_from_le_slice(&bs[4..8]).unwrap(),
            u32::try_from_le_slice(&bs[8..12]).unwrap(),
        );
        i
    }
}

// SAFETY: BIT_CAPACITY is 0.
unsafe impl FromBytes for ByteArray {
    const BIT_CAPACITY: usize = 0;
    type Buffer = Vec<u8>;

    fn try_from_le_slice(b: &[u8]) -> Result<Self> {
        Ok(b.to_vec().into())
    }
    fn from_le_bytes(bs: Self::Buffer) -> Self {
        bs.into()
    }
}

// SAFETY: BIT_CAPACITY is 0.
unsafe impl FromBytes for FixedLenByteArray {
    const BIT_CAPACITY: usize = 0;
    type Buffer = Vec<u8>;

    fn try_from_le_slice(b: &[u8]) -> Result<Self> {
        Ok(b.to_vec().into())
    }
    fn from_le_bytes(bs: Self::Buffer) -> Self {
        bs.into()
    }
}

/// Reads `size` of bytes from `src`, and reinterprets them as type `ty`, in
/// little-endian order.
/// This is copied and modified from byteorder crate.
pub(crate) fn read_num_bytes<T>(size: usize, src: &[u8]) -> T
where
    T: FromBytes,
{
    assert!(size <= src.len());
    let mut buffer = <T as FromBytes>::Buffer::default();
    buffer.as_mut()[..size].copy_from_slice(&src[..size]);
    <T>::from_le_bytes(buffer)
}

/// Returns the ceil of value/divisor.
///
/// This function should be removed after
/// [`int_roundings`](https://github.com/rust-lang/rust/issues/88581) is stable.
#[inline]
pub fn ceil<T: num::Integer>(value: T, divisor: T) -> T {
    num::Integer::div_ceil(&value, &divisor)
}

/// Returns the `num_bits` least-significant bits of `v`
#[inline]
pub fn trailing_bits(v: u64, num_bits: usize) -> u64 {
    if num_bits >= 64 {
        v
    } else {
        v & ((1 << num_bits) - 1)
    }
}

/// Returns the minimum number of bits needed to represent the value 'x'
#[inline]
pub fn num_required_bits(x: u64) -> u8 {
    64 - x.leading_zeros() as u8
}

static BIT_MASK: [u8; 8] = [1, 2, 4, 8, 16, 32, 64, 128];

/// Returns whether bit at position `i` in `data` is set or not
#[inline]
pub fn get_bit(data: &[u8], i: usize) -> bool {
    (data[i >> 3] & BIT_MASK[i & 7]) != 0
}

/// Utility class for writing bit/byte streams. This class can write data in either
/// bit packed or byte aligned fashion.
pub struct BitWriter {
    buffer: Vec<u8>,
    buffered_values: u64,
    bit_offset: u8,
}

impl BitWriter {
    pub fn new(initial_capacity: usize) -> Self {
        Self {
            buffer: Vec::with_capacity(initial_capacity),
            buffered_values: 0,
            bit_offset: 0,
        }
    }

    /// Initializes the writer appending to the existing buffer `buffer`
    pub fn new_from_buf(buffer: Vec<u8>) -> Self {
        Self {
            buffer,
            buffered_values: 0,
            bit_offset: 0,
        }
    }

    /// Consumes and returns the current buffer.
    #[inline]
    pub fn consume(mut self) -> Vec<u8> {
        self.flush();
        self.buffer
    }

    /// Flushes the internal buffered bits and returns the buffer's content.
    /// This is a borrow equivalent of `consume` method.
    #[inline]
    pub fn flush_buffer(&mut self) -> &[u8] {
        self.flush();
        self.buffer()
    }

    /// Clears the internal state so the buffer can be reused.
    #[inline]
    pub fn clear(&mut self) {
        self.buffer.clear();
        self.buffered_values = 0;
        self.bit_offset = 0;
    }

    /// Flushes the internal buffered bits and the align the buffer to the next byte.
    #[inline]
    pub fn flush(&mut self) {
        let num_bytes = ceil(self.bit_offset, 8);
        let slice = &self.buffered_values.to_le_bytes()[..num_bytes as usize];
        self.buffer.extend_from_slice(slice);
        self.buffered_values = 0;
        self.bit_offset = 0;
    }

    /// Advances the current offset by skipping `num_bytes`, flushing the internal bit
    /// buffer first.
    /// This is useful when you want to jump over `num_bytes` bytes and come back later
    /// to fill these bytes.
    #[inline]
    pub fn skip(&mut self, num_bytes: usize) -> usize {
        self.flush();
        let result = self.buffer.len();
        self.buffer.extend(std::iter::repeat(0).take(num_bytes));
        result
    }

    /// Returns a slice containing the next `num_bytes` bytes starting from the current
    /// offset, and advances the underlying buffer by `num_bytes`.
    /// This is useful when you want to jump over `num_bytes` bytes and come back later
    /// to fill these bytes.
    #[inline]
    pub fn get_next_byte_ptr(&mut self, num_bytes: usize) -> &mut [u8] {
        let offset = self.skip(num_bytes);
        &mut self.buffer[offset..offset + num_bytes]
    }

    #[inline]
    pub fn bytes_written(&self) -> usize {
        self.buffer.len() + ceil(self.bit_offset, 8) as usize
    }

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

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

    /// Writes the entire byte `value` at the byte `offset`
    pub fn write_at(&mut self, offset: usize, value: u8) {
        self.buffer[offset] = value;
    }

    /// Writes the `num_bits` LSB of value `v` to the internal buffer of this writer.
    /// The `num_bits` must not be greater than 64. This is bit packed.
    #[inline]
    pub fn put_value(&mut self, v: u64, num_bits: usize) {
        assert!(num_bits <= 64);
        let num_bits = num_bits as u8;
        assert_eq!(v.checked_shr(num_bits as u32).unwrap_or(0), 0); // covers case v >> 64

        // Add value to buffered_values
        self.buffered_values |= v << self.bit_offset;
        self.bit_offset += num_bits;
        if let Some(remaining) = self.bit_offset.checked_sub(64) {
            self.buffer
                .extend_from_slice(&self.buffered_values.to_le_bytes());
            self.bit_offset = remaining;

            // Perform checked right shift: v >> offset, where offset < 64, otherwise we
            // shift all bits
            self.buffered_values = v
                .checked_shr((num_bits - self.bit_offset) as u32)
                .unwrap_or(0);
        }
    }

    /// Writes `val` of `num_bytes` bytes to the next aligned byte. If size of `T` is
    /// larger than `num_bytes`, extra higher ordered bytes will be ignored.
    #[inline]
    pub fn put_aligned<T: AsBytes>(&mut self, val: T, num_bytes: usize) {
        self.flush();
        let slice = val.as_bytes();
        let len = num_bytes.min(slice.len());
        self.buffer.extend_from_slice(&slice[..len]);
    }

    /// Writes `val` of `num_bytes` bytes at the designated `offset`. The `offset` is the
    /// offset starting from the beginning of the internal buffer that this writer
    /// maintains. Note that this will overwrite any existing data between `offset` and
    /// `offset + num_bytes`. Also that if size of `T` is larger than `num_bytes`, extra
    /// higher ordered bytes will be ignored.
    #[inline]
    pub fn put_aligned_offset<T: AsBytes>(&mut self, val: T, num_bytes: usize, offset: usize) {
        let slice = val.as_bytes();
        let len = num_bytes.min(slice.len());
        self.buffer[offset..offset + len].copy_from_slice(&slice[..len])
    }

    /// Writes a VLQ encoded integer `v` to this buffer. The value is byte aligned.
    #[inline]
    pub fn put_vlq_int(&mut self, mut v: u64) {
        while v & 0xFFFFFFFFFFFFFF80 != 0 {
            self.put_aligned::<u8>(((v & 0x7F) | 0x80) as u8, 1);
            v >>= 7;
        }
        self.put_aligned::<u8>((v & 0x7F) as u8, 1);
    }

    /// Writes a zigzag-VLQ encoded (in little endian order) int `v` to this buffer.
    /// Zigzag-VLQ is a variant of VLQ encoding where negative and positive
    /// numbers are encoded in a zigzag fashion.
    /// See: https://developers.google.com/protocol-buffers/docs/encoding
    #[inline]
    pub fn put_zigzag_vlq_int(&mut self, v: i64) {
        let u: u64 = ((v << 1) ^ (v >> 63)) as u64;
        self.put_vlq_int(u)
    }

    /// Returns an estimate of the memory used, in bytes
    pub fn estimated_memory_size(&self) -> usize {
        self.buffer.capacity() * size_of::<u8>()
    }
}

/// Maximum byte length for a VLQ encoded integer
/// MAX_VLQ_BYTE_LEN = 5 for i32, and MAX_VLQ_BYTE_LEN = 10 for i64
pub const MAX_VLQ_BYTE_LEN: usize = 10;

pub struct BitReader {
    /// The byte buffer to read from, passed in by client
    buffer: Bytes,

    /// Bytes are memcpy'd from `buffer` and values are read from this variable.
    /// This is faster than reading values byte by byte directly from `buffer`
    ///
    /// This is only populated when `self.bit_offset != 0`
    buffered_values: u64,

    ///
    /// End                                         Start
    /// |............|B|B|B|B|B|B|B|B|..............|
    ///                   ^          ^
    ///                 bit_offset   byte_offset
    ///
    /// Current byte offset in `buffer`
    byte_offset: usize,

    /// Current bit offset in `buffered_values`
    bit_offset: usize,
}

/// Utility class to read bit/byte stream. This class can read bits or bytes that are
/// either byte aligned or not.
impl BitReader {
    pub fn new(buffer: Bytes) -> Self {
        BitReader {
            buffer,
            buffered_values: 0,
            byte_offset: 0,
            bit_offset: 0,
        }
    }

    pub fn reset(&mut self, buffer: Bytes) {
        self.buffer = buffer;
        self.buffered_values = 0;
        self.byte_offset = 0;
        self.bit_offset = 0;
    }

    /// Gets the current byte offset
    #[inline]
    pub fn get_byte_offset(&self) -> usize {
        self.byte_offset + ceil(self.bit_offset, 8)
    }

    /// Reads a value of type `T` and of size `num_bits`.
    ///
    /// Returns `None` if there's not enough data available. `Some` otherwise.
    pub fn get_value<T: FromBytes>(&mut self, num_bits: usize) -> Option<T> {
        assert!(num_bits <= 64);
        assert!(num_bits <= size_of::<T>() * 8);

        if self.byte_offset * 8 + self.bit_offset + num_bits > self.buffer.len() * 8 {
            return None;
        }

        // If buffer is not byte aligned, `self.buffered_values` will
        // have already been populated
        if self.bit_offset == 0 {
            self.load_buffered_values()
        }

        let mut v =
            trailing_bits(self.buffered_values, self.bit_offset + num_bits) >> self.bit_offset;
        self.bit_offset += num_bits;

        if self.bit_offset >= 64 {
            self.byte_offset += 8;
            self.bit_offset -= 64;

            // If the new bit_offset is not 0, we need to read the next 64-bit chunk
            // to buffered_values and update `v`
            if self.bit_offset != 0 {
                self.load_buffered_values();

                v |= trailing_bits(self.buffered_values, self.bit_offset)
                    .wrapping_shl((num_bits - self.bit_offset) as u32);
            }
        }

        // TODO: better to avoid copying here
        T::try_from_le_slice(v.as_bytes()).ok()
    }

    /// Read multiple values from their packed representation where each element is represented
    /// by `num_bits` bits.
    ///
    /// # Panics
    ///
    /// This function panics if
    /// - `num_bits` is larger than the bit-capacity of `T`
    ///
    pub fn get_batch<T: FromBytes>(&mut self, batch: &mut [T], num_bits: usize) -> usize {
        assert!(num_bits <= size_of::<T>() * 8);

        let mut values_to_read = batch.len();
        let needed_bits = num_bits * values_to_read;
        let remaining_bits = (self.buffer.len() - self.byte_offset) * 8 - self.bit_offset;
        if remaining_bits < needed_bits {
            values_to_read = remaining_bits / num_bits;
        }

        let mut i = 0;

        // First align bit offset to byte offset
        if self.bit_offset != 0 {
            while i < values_to_read && self.bit_offset != 0 {
                batch[i] = self
                    .get_value(num_bits)
                    .expect("expected to have more data");
                i += 1;
            }
        }

        assert_ne!(T::BIT_CAPACITY, 0);
        assert!(num_bits <= T::BIT_CAPACITY);

        // Read directly into output buffer
        match size_of::<T>() {
            1 => {
                let ptr = batch.as_mut_ptr() as *mut u8;
                // SAFETY: batch is properly aligned and sized. Caller guarantees that all bit patterns
                // in which only the lowest T::BIT_CAPACITY bits of T are set are valid,
                // unpack{8,16,32,64} only set to non0 the lowest num_bits bits, and we
                // checked that num_bits <= T::BIT_CAPACITY.
                let out = unsafe { std::slice::from_raw_parts_mut(ptr, batch.len()) };
                while values_to_read - i >= 8 {
                    let out_slice = (&mut out[i..i + 8]).try_into().unwrap();
                    unpack8(&self.buffer[self.byte_offset..], out_slice, num_bits);
                    self.byte_offset += num_bits;
                    i += 8;
                }
            }
            2 => {
                let ptr = batch.as_mut_ptr() as *mut u16;
                // SAFETY: batch is properly aligned and sized. Caller guarantees that all bit patterns
                // in which only the lowest T::BIT_CAPACITY bits of T are set are valid,
                // unpack{8,16,32,64} only set to non0 the lowest num_bits bits, and we
                // checked that num_bits <= T::BIT_CAPACITY.
                let out = unsafe { std::slice::from_raw_parts_mut(ptr, batch.len()) };
                while values_to_read - i >= 16 {
                    let out_slice = (&mut out[i..i + 16]).try_into().unwrap();
                    unpack16(&self.buffer[self.byte_offset..], out_slice, num_bits);
                    self.byte_offset += 2 * num_bits;
                    i += 16;
                }
            }
            4 => {
                let ptr = batch.as_mut_ptr() as *mut u32;
                // SAFETY: batch is properly aligned and sized. Caller guarantees that all bit patterns
                // in which only the lowest T::BIT_CAPACITY bits of T are set are valid,
                // unpack{8,16,32,64} only set to non0 the lowest num_bits bits, and we
                // checked that num_bits <= T::BIT_CAPACITY.
                let out = unsafe { std::slice::from_raw_parts_mut(ptr, batch.len()) };
                while values_to_read - i >= 32 {
                    let out_slice = (&mut out[i..i + 32]).try_into().unwrap();
                    unpack32(&self.buffer[self.byte_offset..], out_slice, num_bits);
                    self.byte_offset += 4 * num_bits;
                    i += 32;
                }
            }
            8 => {
                let ptr = batch.as_mut_ptr() as *mut u64;
                // SAFETY: batch is properly aligned and sized. Caller guarantees that all bit patterns
                // in which only the lowest T::BIT_CAPACITY bits of T are set are valid,
                // unpack{8,16,32,64} only set to non0 the lowest num_bits bits, and we
                // checked that num_bits <= T::BIT_CAPACITY.
                let out = unsafe { std::slice::from_raw_parts_mut(ptr, batch.len()) };
                while values_to_read - i >= 64 {
                    let out_slice = (&mut out[i..i + 64]).try_into().unwrap();
                    unpack64(&self.buffer[self.byte_offset..], out_slice, num_bits);
                    self.byte_offset += 8 * num_bits;
                    i += 64;
                }
            }
            _ => unreachable!(),
        }

        // Try to read smaller batches if possible
        if size_of::<T>() > 4 && values_to_read - i >= 32 && num_bits <= 32 {
            let mut out_buf = [0_u32; 32];
            unpack32(&self.buffer[self.byte_offset..], &mut out_buf, num_bits);
            self.byte_offset += 4 * num_bits;

            for out in out_buf {
                // Zero-allocate buffer
                let mut out_bytes = T::Buffer::default();
                out_bytes.as_mut()[..4].copy_from_slice(&out.to_le_bytes());
                batch[i] = T::from_le_bytes(out_bytes);
                i += 1;
            }
        }

        if size_of::<T>() > 2 && values_to_read - i >= 16 && num_bits <= 16 {
            let mut out_buf = [0_u16; 16];
            unpack16(&self.buffer[self.byte_offset..], &mut out_buf, num_bits);
            self.byte_offset += 2 * num_bits;

            for out in out_buf {
                // Zero-allocate buffer
                let mut out_bytes = T::Buffer::default();
                out_bytes.as_mut()[..2].copy_from_slice(&out.to_le_bytes());
                batch[i] = T::from_le_bytes(out_bytes);
                i += 1;
            }
        }

        if size_of::<T>() > 1 && values_to_read - i >= 8 && num_bits <= 8 {
            let mut out_buf = [0_u8; 8];
            unpack8(&self.buffer[self.byte_offset..], &mut out_buf, num_bits);
            self.byte_offset += num_bits;

            for out in out_buf {
                // Zero-allocate buffer
                let mut out_bytes = T::Buffer::default();
                out_bytes.as_mut()[..1].copy_from_slice(&out.to_le_bytes());
                batch[i] = T::from_le_bytes(out_bytes);
                i += 1;
            }
        }

        // Read any trailing values
        while i < values_to_read {
            let value = self
                .get_value(num_bits)
                .expect("expected to have more data");
            batch[i] = value;
            i += 1;
        }

        values_to_read
    }

    /// Skip num_value values with num_bits bit width
    ///
    /// Return the number of values skipped (up to num_values)
    pub fn skip(&mut self, num_values: usize, num_bits: usize) -> usize {
        assert!(num_bits <= 64);

        let needed_bits = num_bits * num_values;
        let remaining_bits = (self.buffer.len() - self.byte_offset) * 8 - self.bit_offset;

        let values_to_read = match remaining_bits < needed_bits {
            true => remaining_bits / num_bits,
            false => num_values,
        };

        let end_bit_offset = self.byte_offset * 8 + values_to_read * num_bits + self.bit_offset;

        self.byte_offset = end_bit_offset / 8;
        self.bit_offset = end_bit_offset % 8;

        if self.bit_offset != 0 {
            self.load_buffered_values()
        }

        values_to_read
    }

    /// Reads up to `num_bytes` to `buf` returning the number of bytes read
    pub(crate) fn get_aligned_bytes(&mut self, buf: &mut Vec<u8>, num_bytes: usize) -> usize {
        // Align to byte offset
        self.byte_offset = self.get_byte_offset();
        self.bit_offset = 0;

        let src = &self.buffer[self.byte_offset..];
        let to_read = num_bytes.min(src.len());
        buf.extend_from_slice(&src[..to_read]);

        self.byte_offset += to_read;

        to_read
    }

    /// Reads a `num_bytes`-sized value from this buffer and return it.
    /// `T` needs to be a little-endian native type. The value is assumed to be byte
    /// aligned so the bit reader will be advanced to the start of the next byte before
    /// reading the value.
    ///
    /// Returns `Some` if there's enough bytes left to form a value of `T`.
    /// Otherwise `None`.
    pub fn get_aligned<T: FromBytes>(&mut self, num_bytes: usize) -> Option<T> {
        self.byte_offset = self.get_byte_offset();
        self.bit_offset = 0;

        if self.byte_offset + num_bytes > self.buffer.len() {
            return None;
        }

        // Advance byte_offset to next unread byte and read num_bytes
        let v = read_num_bytes::<T>(num_bytes, &self.buffer[self.byte_offset..]);
        self.byte_offset += num_bytes;

        Some(v)
    }

    /// Reads a VLQ encoded (in little endian order) int from the stream.
    /// The encoded int must start at the beginning of a byte.
    ///
    /// Returns `None` if there's not enough bytes in the stream. `Some` otherwise.
    pub fn get_vlq_int(&mut self) -> Option<i64> {
        let mut shift = 0;
        let mut v: i64 = 0;
        while let Some(byte) = self.get_aligned::<u8>(1) {
            v |= ((byte & 0x7F) as i64) << shift;
            shift += 7;
            assert!(
                shift <= MAX_VLQ_BYTE_LEN * 7,
                "Num of bytes exceed MAX_VLQ_BYTE_LEN ({MAX_VLQ_BYTE_LEN})"
            );
            if byte & 0x80 == 0 {
                return Some(v);
            }
        }
        None
    }

    /// Reads a zigzag-VLQ encoded (in little endian order) int from the stream
    /// Zigzag-VLQ is a variant of VLQ encoding where negative and positive numbers are
    /// encoded in a zigzag fashion.
    /// See: https://developers.google.com/protocol-buffers/docs/encoding
    ///
    /// Note: the encoded int must start at the beginning of a byte.
    ///
    /// Returns `None` if the number of bytes there's not enough bytes in the stream.
    /// `Some` otherwise.
    #[inline]
    pub fn get_zigzag_vlq_int(&mut self) -> Option<i64> {
        self.get_vlq_int().map(|v| {
            let u = v as u64;
            (u >> 1) as i64 ^ -((u & 1) as i64)
        })
    }

    /// Loads up to the the next 8 bytes from `self.buffer` at `self.byte_offset`
    /// into `self.buffered_values`.
    ///
    /// Reads fewer than 8 bytes if there are fewer than 8 bytes left
    #[inline]
    fn load_buffered_values(&mut self) {
        let bytes_to_read = cmp::min(self.buffer.len() - self.byte_offset, 8);
        self.buffered_values =
            read_num_bytes::<u64>(bytes_to_read, &self.buffer[self.byte_offset..]);
    }
}

impl From<Vec<u8>> for BitReader {
    #[inline]
    fn from(buffer: Vec<u8>) -> Self {
        BitReader::new(buffer.into())
    }
}

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

    use crate::util::test_common::rand_gen::random_numbers;
    use rand::distributions::{Distribution, Standard};
    use std::fmt::Debug;

    #[test]
    fn test_ceil() {
        assert_eq!(ceil(0, 1), 0);
        assert_eq!(ceil(1, 1), 1);
        assert_eq!(ceil(1, 2), 1);
        assert_eq!(ceil(1, 8), 1);
        assert_eq!(ceil(7, 8), 1);
        assert_eq!(ceil(8, 8), 1);
        assert_eq!(ceil(9, 8), 2);
        assert_eq!(ceil(9, 9), 1);
        assert_eq!(ceil(10000000000_u64, 10), 1000000000);
        assert_eq!(ceil(10_u64, 10000000000), 1);
        assert_eq!(ceil(10000000000_u64, 1000000000), 10);
    }

    #[test]
    fn test_bit_reader_get_byte_offset() {
        let buffer = vec![255; 10];
        let mut bit_reader = BitReader::from(buffer);
        assert_eq!(bit_reader.get_byte_offset(), 0); // offset (0 bytes, 0 bits)
        bit_reader.get_value::<i32>(6);
        assert_eq!(bit_reader.get_byte_offset(), 1); // offset (0 bytes, 6 bits)
        bit_reader.get_value::<i32>(10);
        assert_eq!(bit_reader.get_byte_offset(), 2); // offset (0 bytes, 16 bits)
        bit_reader.get_value::<i32>(20);
        assert_eq!(bit_reader.get_byte_offset(), 5); // offset (0 bytes, 36 bits)
        bit_reader.get_value::<i32>(30);
        assert_eq!(bit_reader.get_byte_offset(), 9); // offset (8 bytes, 2 bits)
    }

    #[test]
    fn test_bit_reader_get_value() {
        let buffer = vec![255, 0];
        let mut bit_reader = BitReader::from(buffer);
        assert_eq!(bit_reader.get_value::<i32>(1), Some(1));
        assert_eq!(bit_reader.get_value::<i32>(2), Some(3));
        assert_eq!(bit_reader.get_value::<i32>(3), Some(7));
        assert_eq!(bit_reader.get_value::<i32>(4), Some(3));
    }

    #[test]
    fn test_bit_reader_skip() {
        let buffer = vec![255, 0];
        let mut bit_reader = BitReader::from(buffer);
        let skipped = bit_reader.skip(1, 1);
        assert_eq!(skipped, 1);
        assert_eq!(bit_reader.get_value::<i32>(1), Some(1));
        let skipped = bit_reader.skip(2, 2);
        assert_eq!(skipped, 2);
        assert_eq!(bit_reader.get_value::<i32>(2), Some(3));
        let skipped = bit_reader.skip(4, 1);
        assert_eq!(skipped, 4);
        assert_eq!(bit_reader.get_value::<i32>(4), Some(0));
        let skipped = bit_reader.skip(1, 1);
        assert_eq!(skipped, 0);
    }

    #[test]
    fn test_bit_reader_get_value_boundary() {
        let buffer = vec![10, 0, 0, 0, 20, 0, 30, 0, 0, 0, 40, 0];
        let mut bit_reader = BitReader::from(buffer);
        assert_eq!(bit_reader.get_value::<i64>(32), Some(10));
        assert_eq!(bit_reader.get_value::<i64>(16), Some(20));
        assert_eq!(bit_reader.get_value::<i64>(32), Some(30));
        assert_eq!(bit_reader.get_value::<i64>(16), Some(40));
    }

    #[test]
    fn test_bit_reader_skip_boundary() {
        let buffer = vec![10, 0, 0, 0, 20, 0, 30, 0, 0, 0, 40, 0];
        let mut bit_reader = BitReader::from(buffer);
        assert_eq!(bit_reader.get_value::<i64>(32), Some(10));
        assert_eq!(bit_reader.skip(1, 16), 1);
        assert_eq!(bit_reader.get_value::<i64>(32), Some(30));
        assert_eq!(bit_reader.get_value::<i64>(16), Some(40));
    }

    #[test]
    fn test_bit_reader_get_aligned() {
        // 01110101 11001011
        let buffer = Bytes::from(vec![0x75, 0xCB]);
        let mut bit_reader = BitReader::new(buffer.clone());
        assert_eq!(bit_reader.get_value::<i32>(3), Some(5));
        assert_eq!(bit_reader.get_aligned::<i32>(1), Some(203));
        assert_eq!(bit_reader.get_value::<i32>(1), None);
        bit_reader.reset(buffer.clone());
        assert_eq!(bit_reader.get_aligned::<i32>(3), None);
    }

    #[test]
    fn test_bit_reader_get_vlq_int() {
        // 10001001 00000001 11110010 10110101 00000110
        let buffer: Vec<u8> = vec![0x89, 0x01, 0xF2, 0xB5, 0x06];
        let mut bit_reader = BitReader::from(buffer);
        assert_eq!(bit_reader.get_vlq_int(), Some(137));
        assert_eq!(bit_reader.get_vlq_int(), Some(105202));
    }

    #[test]
    fn test_bit_reader_get_zigzag_vlq_int() {
        let buffer: Vec<u8> = vec![0, 1, 2, 3];
        let mut bit_reader = BitReader::from(buffer);
        assert_eq!(bit_reader.get_zigzag_vlq_int(), Some(0));
        assert_eq!(bit_reader.get_zigzag_vlq_int(), Some(-1));
        assert_eq!(bit_reader.get_zigzag_vlq_int(), Some(1));
        assert_eq!(bit_reader.get_zigzag_vlq_int(), Some(-2));
    }

    #[test]
    fn test_num_required_bits() {
        assert_eq!(num_required_bits(0), 0);
        assert_eq!(num_required_bits(1), 1);
        assert_eq!(num_required_bits(2), 2);
        assert_eq!(num_required_bits(4), 3);
        assert_eq!(num_required_bits(8), 4);
        assert_eq!(num_required_bits(10), 4);
        assert_eq!(num_required_bits(12), 4);
        assert_eq!(num_required_bits(16), 5);
        assert_eq!(num_required_bits(u64::MAX), 64);
    }

    #[test]
    fn test_get_bit() {
        // 00001101
        assert!(get_bit(&[0b00001101], 0));
        assert!(!get_bit(&[0b00001101], 1));
        assert!(get_bit(&[0b00001101], 2));
        assert!(get_bit(&[0b00001101], 3));

        // 01001001 01010010
        assert!(get_bit(&[0b01001001, 0b01010010], 0));
        assert!(!get_bit(&[0b01001001, 0b01010010], 1));
        assert!(!get_bit(&[0b01001001, 0b01010010], 2));
        assert!(get_bit(&[0b01001001, 0b01010010], 3));
        assert!(!get_bit(&[0b01001001, 0b01010010], 4));
        assert!(!get_bit(&[0b01001001, 0b01010010], 5));
        assert!(get_bit(&[0b01001001, 0b01010010], 6));
        assert!(!get_bit(&[0b01001001, 0b01010010], 7));
        assert!(!get_bit(&[0b01001001, 0b01010010], 8));
        assert!(get_bit(&[0b01001001, 0b01010010], 9));
        assert!(!get_bit(&[0b01001001, 0b01010010], 10));
        assert!(!get_bit(&[0b01001001, 0b01010010], 11));
        assert!(get_bit(&[0b01001001, 0b01010010], 12));
        assert!(!get_bit(&[0b01001001, 0b01010010], 13));
        assert!(get_bit(&[0b01001001, 0b01010010], 14));
        assert!(!get_bit(&[0b01001001, 0b01010010], 15));
    }

    #[test]
    fn test_skip() {
        let mut writer = BitWriter::new(5);
        let old_offset = writer.skip(1);
        writer.put_aligned(42, 4);
        writer.put_aligned_offset(0x10, 1, old_offset);
        let result = writer.consume();
        assert_eq!(result.as_ref(), [0x10, 42, 0, 0, 0]);

        writer = BitWriter::new(4);
        let result = writer.skip(5);
        assert_eq!(result, 0);
        assert_eq!(writer.buffer(), &[0; 5])
    }

    #[test]
    fn test_get_next_byte_ptr() {
        let mut writer = BitWriter::new(5);
        {
            let first_byte = writer.get_next_byte_ptr(1);
            first_byte[0] = 0x10;
        }
        writer.put_aligned(42, 4);
        let result = writer.consume();
        assert_eq!(result.as_ref(), [0x10, 42, 0, 0, 0]);
    }

    #[test]
    fn test_consume_flush_buffer() {
        let mut writer1 = BitWriter::new(3);
        let mut writer2 = BitWriter::new(3);
        for i in 1..10 {
            writer1.put_value(i, 4);
            writer2.put_value(i, 4);
        }
        let res1 = writer1.flush_buffer();
        let res2 = writer2.consume();
        assert_eq!(res1, &res2[..]);
    }

    #[test]
    fn test_put_get_bool() {
        let len = 8;
        let mut writer = BitWriter::new(len);

        for i in 0..8 {
            writer.put_value(i % 2, 1);
        }

        writer.flush();
        {
            let buffer = writer.buffer();
            assert_eq!(buffer[0], 0b10101010);
        }

        // Write 00110011
        for i in 0..8 {
            match i {
                0 | 1 | 4 | 5 => writer.put_value(false as u64, 1),
                _ => writer.put_value(true as u64, 1),
            }
        }
        writer.flush();
        {
            let buffer = writer.buffer();
            assert_eq!(buffer[0], 0b10101010);
            assert_eq!(buffer[1], 0b11001100);
        }

        let mut reader = BitReader::from(writer.consume());

        for i in 0..8 {
            let val = reader
                .get_value::<u8>(1)
                .expect("get_value() should return OK");
            assert_eq!(val, i % 2);
        }

        for i in 0..8 {
            let val = reader
                .get_value::<bool>(1)
                .expect("get_value() should return OK");
            match i {
                0 | 1 | 4 | 5 => assert!(!val),
                _ => assert!(val),
            }
        }
    }

    #[test]
    fn test_put_value_roundtrip() {
        test_put_value_rand_numbers(32, 2);
        test_put_value_rand_numbers(32, 3);
        test_put_value_rand_numbers(32, 4);
        test_put_value_rand_numbers(32, 5);
        test_put_value_rand_numbers(32, 6);
        test_put_value_rand_numbers(32, 7);
        test_put_value_rand_numbers(32, 8);
        test_put_value_rand_numbers(64, 16);
        test_put_value_rand_numbers(64, 24);
        test_put_value_rand_numbers(64, 32);
    }

    fn test_put_value_rand_numbers(total: usize, num_bits: usize) {
        assert!(num_bits < 64);
        let num_bytes = ceil(num_bits, 8);
        let mut writer = BitWriter::new(num_bytes * total);
        let values: Vec<u64> = random_numbers::<u64>(total)
            .iter()
            .map(|v| v & ((1 << num_bits) - 1))
            .collect();
        (0..total).for_each(|i| writer.put_value(values[i], num_bits));

        let mut reader = BitReader::from(writer.consume());
        (0..total).for_each(|i| {
            let v = reader
                .get_value::<u64>(num_bits)
                .expect("get_value() should return OK");
            assert_eq!(
                v, values[i],
                "[{}]: expected {} but got {}",
                i, values[i], v
            );
        });
    }

    #[test]
    fn test_get_batch() {
        const SIZE: &[usize] = &[1, 31, 32, 33, 128, 129];
        for s in SIZE {
            for i in 0..=64 {
                match i {
                    0..=8 => test_get_batch_helper::<u8>(*s, i),
                    9..=16 => test_get_batch_helper::<u16>(*s, i),
                    17..=32 => test_get_batch_helper::<u32>(*s, i),
                    _ => test_get_batch_helper::<u64>(*s, i),
                }
            }
        }
    }

    fn test_get_batch_helper<T>(total: usize, num_bits: usize)
    where
        T: FromBytes + Default + Clone + Debug + Eq,
    {
        assert!(num_bits <= 64);
        let num_bytes = ceil(num_bits, 8);
        let mut writer = BitWriter::new(num_bytes * total);

        let mask = match num_bits {
            64 => u64::MAX,
            _ => (1 << num_bits) - 1,
        };

        let values: Vec<u64> = random_numbers::<u64>(total)
            .iter()
            .map(|v| v & mask)
            .collect();

        // Generic values used to check against actual values read from `get_batch`.
        let expected_values: Vec<T> = values
            .iter()
            .map(|v| T::try_from_le_slice(v.as_bytes()).unwrap())
            .collect();

        (0..total).for_each(|i| writer.put_value(values[i], num_bits));

        let buf = writer.consume();
        let mut reader = BitReader::from(buf);
        let mut batch = vec![T::default(); values.len()];
        let values_read = reader.get_batch::<T>(&mut batch, num_bits);
        assert_eq!(values_read, values.len());
        for i in 0..batch.len() {
            assert_eq!(
                batch[i],
                expected_values[i],
                "max_num_bits = {}, num_bits = {}, index = {}",
                size_of::<T>() * 8,
                num_bits,
                i
            );
        }
    }

    #[test]
    fn test_put_aligned_roundtrip() {
        test_put_aligned_rand_numbers::<u8>(4, 3);
        test_put_aligned_rand_numbers::<u8>(16, 5);
        test_put_aligned_rand_numbers::<i16>(32, 7);
        test_put_aligned_rand_numbers::<i16>(32, 9);
        test_put_aligned_rand_numbers::<i32>(32, 11);
        test_put_aligned_rand_numbers::<i32>(32, 13);
        test_put_aligned_rand_numbers::<i64>(32, 17);
        test_put_aligned_rand_numbers::<i64>(32, 23);
    }

    fn test_put_aligned_rand_numbers<T>(total: usize, num_bits: usize)
    where
        T: Copy + FromBytes + AsBytes + Debug + PartialEq,
        Standard: Distribution<T>,
    {
        assert!(num_bits <= 32);
        assert!(total % 2 == 0);

        let aligned_value_byte_width = std::mem::size_of::<T>();
        let value_byte_width = ceil(num_bits, 8);
        let mut writer =
            BitWriter::new((total / 2) * (aligned_value_byte_width + value_byte_width));
        let values: Vec<u32> = random_numbers::<u32>(total / 2)
            .iter()
            .map(|v| v & ((1 << num_bits) - 1))
            .collect();
        let aligned_values = random_numbers::<T>(total / 2);

        for i in 0..total {
            let j = i / 2;
            if i % 2 == 0 {
                writer.put_value(values[j] as u64, num_bits);
            } else {
                writer.put_aligned::<T>(aligned_values[j], aligned_value_byte_width)
            }
        }

        let mut reader = BitReader::from(writer.consume());
        for i in 0..total {
            let j = i / 2;
            if i % 2 == 0 {
                let v = reader
                    .get_value::<u64>(num_bits)
                    .expect("get_value() should return OK");
                assert_eq!(
                    v, values[j] as u64,
                    "[{}]: expected {} but got {}",
                    i, values[j], v
                );
            } else {
                let v = reader
                    .get_aligned::<T>(aligned_value_byte_width)
                    .expect("get_aligned() should return OK");
                assert_eq!(
                    v, aligned_values[j],
                    "[{}]: expected {:?} but got {:?}",
                    i, aligned_values[j], v
                );
            }
        }
    }

    #[test]
    fn test_put_vlq_int() {
        let total = 64;
        let mut writer = BitWriter::new(total * 32);
        let values = random_numbers::<u32>(total);
        (0..total).for_each(|i| writer.put_vlq_int(values[i] as u64));

        let mut reader = BitReader::from(writer.consume());
        (0..total).for_each(|i| {
            let v = reader
                .get_vlq_int()
                .expect("get_vlq_int() should return OK");
            assert_eq!(
                v as u32, values[i],
                "[{}]: expected {} but got {}",
                i, values[i], v
            );
        });
    }

    #[test]
    fn test_put_zigzag_vlq_int() {
        let total = 64;
        let mut writer = BitWriter::new(total * 32);
        let values = random_numbers::<i32>(total);
        (0..total).for_each(|i| writer.put_zigzag_vlq_int(values[i] as i64));

        let mut reader = BitReader::from(writer.consume());
        (0..total).for_each(|i| {
            let v = reader
                .get_zigzag_vlq_int()
                .expect("get_zigzag_vlq_int() should return OK");
            assert_eq!(
                v as i32, values[i],
                "[{}]: expected {} but got {}",
                i, values[i], v
            );
        });
    }

    #[test]
    fn test_get_batch_zero_extend() {
        let to_read = vec![0xFF; 4];
        let mut reader = BitReader::from(to_read);

        // Create a non-zeroed output buffer
        let mut output = [u64::MAX; 32];
        reader.get_batch(&mut output, 1);

        for v in output {
            // Values should be read correctly
            assert_eq!(v, 1);
        }
    }
}