dsi-bitstream 0.7.0

/*
 * SPDX-FileCopyrightText: 2023 Tommaso Fontana
 * SPDX-FileCopyrightText: 2023 Inria
 * SPDX-FileCopyrightText: 2023 Sebastiano Vigna
 *
 * SPDX-License-Identifier: Apache-2.0 OR LGPL-2.1-or-later
 */

use core::any::TypeId;
use core::{mem, ptr};

use crate::codes::params::{DefaultWriteParams, WriteParams};
use crate::traits::*;
use common_traits::{AsBytes, CastableInto, FiniteRangeNumber, Integer, Number};
#[cfg(feature = "mem_dbg")]
use mem_dbg::{MemDbg, MemSize};

/// An implementation of [`BitWrite`] for a [`WordWrite`].
///
/// This implementation uses a bit buffer to store bits that are not yet
/// written. The size of the bit buffer is the size of the word used by the
/// [`WordWrite`], which on most platform should be `usize`.
///
/// The additional type parameter `WP` is used to select the parameters for the
/// instantaneous codes, but the casual user should be happy with the default
/// value. See [`WriteParams`] for more details.
///
/// The convenience methods [`from_path`] and [`from_file`] create a
/// [`BufBitWriter`] around a buffered file writer.
///
/// For additional flexibility, this structures implements [`std::io::Write`].
/// Note that because of coherence rules it is not possible to implement
/// [`std::io::Write`] for a generic [`BitWrite`].

#[derive(Debug)]
#[cfg_attr(feature = "mem_dbg", derive(MemDbg, MemSize))]
pub struct BufBitWriter<E: Endianness, WW: WordWrite, WP: WriteParams = DefaultWriteParams> {
    /// The [`WordWrite`] to which we will write words.
    backend: WW,
    /// The buffer where we store bits until we have a word worth of them.
    /// It might be empty, but it is never full.
    /// Only the lower (BE) or upper (LE) `WW::Word::BITS - space_left_in_buffer`
    /// bits are valid: the rest have undefined value.
    buffer: WW::Word,
    /// Number of upper (BE) or lower (LE) free bits in the buffer. It is always greater than zero.
    space_left_in_buffer: usize,
    _marker_endianness: core::marker::PhantomData<(E, WP)>,
}

/// Creates a new [`BufBitWriter`] with [default read
/// parameters](`DefaultWriteParams`) from a file path using the provided
/// endianness and read word.
///
/// # Examples
///
/// ```no_run
/// use dsi_bitstream::prelude::*;
/// let mut writer = buf_bit_writer::from_path::<LE, u64>("data.bin")?;
/// # Ok::<(), Box<dyn std::error::Error>>(())
/// ```
#[cfg(feature = "std")]
pub fn from_path<E: Endianness, W: Word>(
    path: impl AsRef<std::path::Path>,
) -> anyhow::Result<
    BufBitWriter<E, super::WordAdapter<W, std::io::BufWriter<std::fs::File>>, DefaultWriteParams>,
> {
    Ok(from_file::<E, W>(std::fs::File::create(path)?))
}

/// Creates a new [`BufBitWriter`] with [default read
/// parameters](`DefaultWriteParams`) from a file path using the provided
/// endianness and read word.
///
/// See also [`from_path`] for a version that takes a path.
#[cfg(feature = "std")]
pub fn from_file<E: Endianness, W: Word>(
    file: std::fs::File,
) -> BufBitWriter<E, super::WordAdapter<W, std::io::BufWriter<std::fs::File>>, DefaultWriteParams> {
    BufBitWriter::<E, super::WordAdapter<W, std::io::BufWriter<std::fs::File>>>::new(
        super::WordAdapter::new(std::io::BufWriter::new(file)),
    )
}

impl<E: Endianness, WW: WordWrite, WP: WriteParams> BufBitWriter<E, WW, WP> {
    /// Creates a new [`BufBitWriter`] around a [`WordWrite`].
    ///
    /// ### Example
    /// ```
    /// #[cfg(not(feature = "std"))]
    /// # fn main() {}
    /// # #[cfg(feature = "std")]
    /// # fn main() {
    /// use dsi_bitstream::prelude::*;
    /// let buffer = Vec::<usize>::new();
    /// let word_writer = MemWordWriterVec::new(buffer);
    /// let mut buf_bit_writer = <BufBitWriter<BE, _>>::new(word_writer);
    /// # }
    /// ```
    pub fn new(backend: WW) -> Self {
        Self {
            backend,
            buffer: WW::Word::ZERO,
            space_left_in_buffer: WW::Word::BITS,
            _marker_endianness: core::marker::PhantomData,
        }
    }
}

impl<E: Endianness, WW: WordWrite, WP: WriteParams> BufBitWriter<E, WW, WP>
where
    BufBitWriter<E, WW, WP>: BitWrite<E>,
{
    ///  Return the backend, consuming this writer after
    /// [flushing it](BufBitWriter::flush).
    pub fn into_inner(mut self) -> Result<WW, <Self as BitWrite<E>>::Error> {
        self.flush()?;
        // SAFETY: forget(self) prevents double dropping backend
        let backend = unsafe { ptr::read(&self.backend) };
        mem::forget(self);
        Ok(backend)
    }
}

impl<E: Endianness, WW: WordWrite, WP: WriteParams> core::ops::Drop for BufBitWriter<E, WW, WP> {
    fn drop(&mut self) {
        if TypeId::of::<E>() == TypeId::of::<LE>() {
            flush_le(self).unwrap();
        } else {
            // TypeId::of::<E>() = TypeId::of::<BE>()
            flush_be(self).unwrap();
        }
    }
}

/// Helper function flushing a [`BufBitWriter`] in big-endian fashion.
///
/// The endianness is hardwired because the function is called
/// from [`BufBitWriter::drop`] using a check on the
/// [`TypeId`] of the endianness.
fn flush_be<E: Endianness, WW: WordWrite, WP: WriteParams>(
    buf_bit_writer: &mut BufBitWriter<E, WW, WP>,
) -> Result<usize, WW::Error> {
    let to_flush = WW::Word::BITS - buf_bit_writer.space_left_in_buffer;
    if to_flush != 0 {
        buf_bit_writer.buffer <<= buf_bit_writer.space_left_in_buffer;
        buf_bit_writer
            .backend
            .write_word(buf_bit_writer.buffer.to_be())?;
        buf_bit_writer.space_left_in_buffer = WW::Word::BITS;
    }
    buf_bit_writer.backend.flush()?;
    Ok(to_flush)
}

impl<WW: WordWrite, WP: WriteParams> BitWrite<BE> for BufBitWriter<BE, WW, WP>
where
    u64: CastableInto<WW::Word>,
{
    type Error = <WW as WordWrite>::Error;

    fn flush(&mut self) -> Result<usize, Self::Error> {
        flush_be(self)
    }

    #[allow(unused_mut)]
    #[inline]
    fn write_bits(&mut self, mut value: u64, n_bits: usize) -> Result<usize, Self::Error> {
        debug_assert!(n_bits <= 64);
        #[cfg(feature = "checks")]
        assert!(
            value & (1_u128 << n_bits).wrapping_sub(1) as u64 == value,
            "Error: value {} does not fit in {} bits",
            value,
            n_bits
        );
        debug_assert!(self.space_left_in_buffer > 0);

        #[cfg(test)]
        if n_bits < 64 {
            // We put garbage in the higher bits for testing
            value |= u64::MAX << n_bits;
        }

        // Easy way out: we fit the buffer
        if n_bits < self.space_left_in_buffer {
            self.buffer <<= n_bits;
            // Clean up bits higher than n_bits
            self.buffer |= value.cast() & !(WW::Word::MAX << n_bits as u32);
            self.space_left_in_buffer -= n_bits;
            return Ok(n_bits);
        }

        // Load the bottom of the buffer, if necessary, and dump the whole buffer
        self.buffer = self.buffer << (self.space_left_in_buffer - 1) << 1;
        // The first shift discards bits higher than n_bits
        self.buffer |= (value << (64 - n_bits) >> (64 - self.space_left_in_buffer)).cast();
        self.backend.write_word(self.buffer.to_be())?;

        let mut to_write = n_bits - self.space_left_in_buffer;

        for _ in 0..to_write / WW::Word::BITS {
            to_write -= WW::Word::BITS;
            self.backend
                .write_word((value >> to_write).cast().to_be())?;
        }

        self.space_left_in_buffer = WW::Word::BITS - to_write;
        self.buffer = value.cast();
        Ok(n_bits)
    }

    #[inline(always)]
    #[allow(clippy::collapsible_if)]
    fn write_unary(&mut self, mut value: u64) -> Result<usize, Self::Error> {
        debug_assert!(value < u64::MAX);
        debug_assert!(self.space_left_in_buffer > 0);

        let code_length = value + 1;

        // Easy way out: we fit the buffer
        if code_length <= self.space_left_in_buffer as u64 {
            self.space_left_in_buffer -= code_length as usize;
            self.buffer = self.buffer << value << 1;
            self.buffer |= WW::Word::ONE;
            if self.space_left_in_buffer == 0 {
                self.backend.write_word(self.buffer.to_be())?;
                self.space_left_in_buffer = WW::Word::BITS;
            }
            return Ok(code_length as usize);
        }

        self.buffer = self.buffer << (self.space_left_in_buffer - 1) << 1;
        self.backend.write_word(self.buffer.to_be())?;

        value -= self.space_left_in_buffer as u64;

        for _ in 0..value / WW::Word::BITS as u64 {
            self.backend.write_word(WW::Word::ZERO)?;
        }

        value %= WW::Word::BITS as u64;

        if value == WW::Word::BITS as u64 - 1 {
            self.backend.write_word(WW::Word::ONE.to_be())?;
            self.space_left_in_buffer = WW::Word::BITS;
        } else {
            self.buffer = WW::Word::ONE;
            self.space_left_in_buffer = WW::Word::BITS - (value as usize + 1);
        }

        Ok(code_length as usize)
    }

    #[cfg(not(feature = "no_copy_impls"))]
    fn copy_from<F: Endianness, R: BitRead<F>>(
        &mut self,
        bit_read: &mut R,
        mut n: u64,
    ) -> Result<(), CopyError<R::Error, Self::Error>> {
        if n < self.space_left_in_buffer as u64 {
            self.buffer = (self.buffer << n)
                | bit_read
                    .read_bits(n as usize)
                    .map_err(CopyError::ReadError)?
                    .cast();
            self.space_left_in_buffer -= n as usize;
            return Ok(());
        }

        self.buffer = (self.buffer << (self.space_left_in_buffer - 1) << 1)
            | bit_read
                .read_bits(self.space_left_in_buffer)
                .map_err(CopyError::ReadError)?
                .cast();
        n -= self.space_left_in_buffer as u64;

        self.backend
            .write_word(self.buffer.to_be())
            .map_err(CopyError::WriteError)?;

        for _ in 0..n / WW::Word::BITS as u64 {
            self.backend
                .write_word(
                    bit_read
                        .read_bits(WW::Word::BITS)
                        .map_err(CopyError::ReadError)?
                        .cast()
                        .to_be(),
                )
                .map_err(CopyError::WriteError)?;
        }

        n %= WW::Word::BITS as u64;
        self.buffer = bit_read
            .read_bits(n as usize)
            .map_err(CopyError::ReadError)?
            .cast();
        self.space_left_in_buffer = WW::Word::BITS - n as usize;

        Ok(())
    }
}

/// Helper function flushing a [`BufBitWriter`] in big-endian fashion.
///
/// The endianness is hardwired because the function is called
/// from [`BufBitWriter::drop`] using a check on the
/// [`TypeId`] of the endianness.
fn flush_le<E: Endianness, WW: WordWrite, WP: WriteParams>(
    buf_bit_writer: &mut BufBitWriter<E, WW, WP>,
) -> Result<usize, WW::Error> {
    let to_flush = WW::Word::BITS - buf_bit_writer.space_left_in_buffer;
    if to_flush != 0 {
        buf_bit_writer.buffer >>= buf_bit_writer.space_left_in_buffer;
        buf_bit_writer
            .backend
            .write_word(buf_bit_writer.buffer.to_le())?;
        buf_bit_writer.space_left_in_buffer = WW::Word::BITS;
    }
    buf_bit_writer.backend.flush()?;
    Ok(to_flush)
}

impl<WW: WordWrite, WP: WriteParams> BitWrite<LE> for BufBitWriter<LE, WW, WP>
where
    u64: CastableInto<WW::Word>,
{
    type Error = <WW as WordWrite>::Error;

    fn flush(&mut self) -> Result<usize, Self::Error> {
        flush_le(self)
    }

    #[inline]
    fn write_bits(&mut self, mut value: u64, n_bits: usize) -> Result<usize, Self::Error> {
        debug_assert!(n_bits <= 64);
        #[cfg(feature = "checks")]
        assert!(
            value & (1_u128 << n_bits).wrapping_sub(1) as u64 == value,
            "Error: value {} does not fit in {} bits",
            value,
            n_bits
        );
        debug_assert!(self.space_left_in_buffer > 0);

        #[cfg(test)]
        if n_bits < 64 {
            // We put garbage in the higher bits for testing
            value |= u64::MAX << n_bits;
        }

        // Easy way out: we fit the buffer
        if n_bits < self.space_left_in_buffer {
            self.buffer >>= n_bits;
            // Clean up bits higher than n_bits
            self.buffer |=
                (value.cast() & !(WW::Word::MAX << n_bits as u32)).rotate_right(n_bits as u32);
            self.space_left_in_buffer -= n_bits;
            return Ok(n_bits);
        }

        // Load the top of the buffer, if necessary, and dump the whole buffer
        self.buffer = self.buffer >> (self.space_left_in_buffer - 1) >> 1;
        self.buffer |= value.cast() << (WW::Word::BITS - self.space_left_in_buffer);
        self.backend.write_word(self.buffer.to_le())?;

        let to_write = n_bits - self.space_left_in_buffer;
        value = value >> (self.space_left_in_buffer - 1) >> 1;

        for _ in 0..to_write / WW::Word::BITS {
            self.backend.write_word(value.cast().to_le())?;
            // This cannot be executed with WW::Word::BITS >= 64
            value >>= WW::Word::BITS;
        }

        self.space_left_in_buffer = WW::Word::BITS - to_write % WW::Word::BITS;
        self.buffer = value.cast().rotate_right(to_write as u32);
        Ok(n_bits)
    }

    #[inline(always)]
    #[allow(clippy::collapsible_if)]
    fn write_unary(&mut self, mut value: u64) -> Result<usize, Self::Error> {
        debug_assert!(value < u64::MAX);
        debug_assert!(self.space_left_in_buffer > 0);

        let code_length = value + 1;

        // Easy way out: we fit the buffer
        if code_length <= self.space_left_in_buffer as u64 {
            self.space_left_in_buffer -= code_length as usize;
            self.buffer = self.buffer >> value >> 1;
            self.buffer |= WW::Word::ONE << (WW::Word::BITS - 1);
            if self.space_left_in_buffer == 0 {
                self.backend.write_word(self.buffer.to_le())?;
                self.space_left_in_buffer = WW::Word::BITS;
            }
            return Ok(code_length as usize);
        }

        self.buffer = self.buffer >> (self.space_left_in_buffer - 1) >> 1;
        self.backend.write_word(self.buffer.to_le())?;

        value -= self.space_left_in_buffer as u64;

        for _ in 0..value / WW::Word::BITS as u64 {
            self.backend.write_word(WW::Word::ZERO)?;
        }

        value %= WW::Word::BITS as u64;

        if value == WW::Word::BITS as u64 - 1 {
            self.backend
                .write_word((WW::Word::ONE << (WW::Word::BITS - 1)).to_le())?;
            self.space_left_in_buffer = WW::Word::BITS;
        } else {
            self.buffer = WW::Word::ONE << (WW::Word::BITS - 1);
            self.space_left_in_buffer = WW::Word::BITS - (value as usize + 1);
        }

        Ok(code_length as usize)
    }

    #[cfg(not(feature = "no_copy_impls"))]
    fn copy_from<F: Endianness, R: BitRead<F>>(
        &mut self,
        bit_read: &mut R,
        mut n: u64,
    ) -> Result<(), CopyError<R::Error, Self::Error>> {
        if n < self.space_left_in_buffer as u64 {
            self.buffer = (self.buffer >> n)
                | (bit_read
                    .read_bits(n as usize)
                    .map_err(CopyError::ReadError)?)
                .cast()
                .rotate_right(n as u32);
            self.space_left_in_buffer -= n as usize;
            return Ok(());
        }

        self.buffer = (self.buffer >> (self.space_left_in_buffer - 1) >> 1)
            | (bit_read
                .read_bits(self.space_left_in_buffer)
                .map_err(CopyError::ReadError)?
                .cast())
            .rotate_right(self.space_left_in_buffer as u32);
        n -= self.space_left_in_buffer as u64;

        self.backend
            .write_word(self.buffer.to_le())
            .map_err(CopyError::WriteError)?;

        for _ in 0..n / WW::Word::BITS as u64 {
            self.backend
                .write_word(
                    bit_read
                        .read_bits(WW::Word::BITS)
                        .map_err(CopyError::ReadError)?
                        .cast()
                        .to_le(),
                )
                .map_err(CopyError::WriteError)?;
        }

        n %= WW::Word::BITS as u64;
        self.buffer = bit_read
            .read_bits(n as usize)
            .map_err(CopyError::ReadError)?
            .cast()
            .rotate_right(n as u32);
        self.space_left_in_buffer = WW::Word::BITS - n as usize;

        Ok(())
    }
}

#[cfg(feature = "std")]
impl<WW: WordWrite, WP: WriteParams> std::io::Write for BufBitWriter<BE, WW, WP>
where
    u64: CastableInto<WW::Word>,
{
    #[inline(always)]
    fn write(&mut self, buf: &[u8]) -> std::io::Result<usize> {
        let mut iter = buf.chunks_exact(WW::Word::BYTES);

        for word in &mut iter {
            self.write_bits(u64::from_be_bytes(word.try_into().unwrap()), 64)
                .map_err(|_| std::io::Error::other("Could not write bits to stream"))?;
        }

        let rem = iter.remainder();
        if !rem.is_empty() {
            let mut word = 0;
            let bits = rem.len() * 8;
            for byte in rem.iter() {
                word <<= 8;
                word |= *byte as u64;
            }
            self.write_bits(word, bits)
                .map_err(|_| std::io::Error::other("Could not write bits to stream"))?;
        }

        Ok(buf.len())
    }

    fn flush(&mut self) -> std::io::Result<()> {
        flush_be(self).map_err(|_| std::io::Error::other("Could not flush bits to stream"))?;
        Ok(())
    }
}

#[cfg(feature = "std")]
impl<WW: WordWrite, WP: WriteParams> std::io::Write for BufBitWriter<LE, WW, WP>
where
    u64: CastableInto<WW::Word>,
{
    #[inline(always)]
    fn write(&mut self, buf: &[u8]) -> std::io::Result<usize> {
        let mut iter = buf.chunks_exact(WW::Word::BYTES);

        for word in &mut iter {
            self.write_bits(u64::from_le_bytes(word.try_into().unwrap()), 64)
                .map_err(|_| std::io::Error::other("Could not write bits to stream"))?;
        }

        let rem = iter.remainder();
        if !rem.is_empty() {
            let mut word = 0;
            let bits = rem.len() * 8;
            for byte in rem.iter().rev() {
                word <<= 8;
                word |= *byte as u64;
            }
            self.write_bits(word, bits)
                .map_err(|_| std::io::Error::other("Could not write bits to stream"))?;
        }

        Ok(buf.len())
    }

    fn flush(&mut self) -> std::io::Result<()> {
        flush_le(self).map_err(|_| std::io::Error::other("Could not flush bits to stream"))?;
        Ok(())
    }
}

#[cfg(test)]
#[cfg(feature = "std")]
mod test {
    use super::*;
    use crate::prelude::MemWordWriterVec;
    use std::io::Write;

    #[test]
    fn test_write() {
        let data = [
            0x90, 0x2d, 0xd0, 0x26, 0xdf, 0x89, 0xbb, 0x7e, 0x3a, 0xd6, 0xc6, 0x96, 0x73, 0xe9,
            0x9d, 0xc9, 0x2a, 0x77, 0x82, 0xa9, 0xe6, 0x4b, 0x53, 0xcc, 0x83, 0x80, 0x4a, 0xf3,
            0xcd, 0xe3, 0x50, 0x4e, 0x45, 0x4a, 0x3a, 0x42, 0x00, 0x4b, 0x4d, 0xbe, 0x4c, 0x88,
            0x24, 0xf2, 0x4b, 0x6b, 0xbd, 0x79, 0xeb, 0x74, 0xbc, 0xe8, 0x7d, 0xff, 0x4b, 0x3d,
            0xa7, 0xd6, 0x0d, 0xef, 0x9c, 0x5b, 0xb3, 0xec, 0x94, 0x97, 0xcc, 0x8b, 0x41, 0xe1,
            0x9c, 0xcc, 0x1a, 0x03, 0x58, 0xc4, 0xfb, 0xd0, 0xc0, 0x10, 0xe2, 0xa0, 0xc9, 0xac,
            0xa7, 0xbb, 0x50, 0xf6, 0x5c, 0x87, 0x68, 0x0f, 0x42, 0x93, 0x3f, 0x2e, 0x28, 0x28,
            0x76, 0x83, 0x9b, 0xeb, 0x12, 0xe0, 0x4f, 0xc5, 0xb0, 0x8d, 0x14, 0xda, 0x3b, 0xdf,
            0xd3, 0x4b, 0x80, 0xd1, 0xfc, 0x87, 0x85, 0xae, 0x54, 0xc7, 0x45, 0xc9, 0x38, 0x43,
            0xa7, 0x9f, 0xdd, 0xa9, 0x71, 0xa7, 0x52, 0x36, 0x82, 0xff, 0x49, 0x55, 0xdb, 0x84,
            0xc2, 0x95, 0xad, 0x45, 0x80, 0xc6, 0x02, 0x80, 0xf8, 0xfc, 0x86, 0x79, 0xae, 0xb9,
            0x57, 0xe7, 0x3b, 0x33, 0x64, 0xa8,
        ];

        for i in 0..data.len() {
            let mut buffer = Vec::<u64>::new();
            let mut writer = BufBitWriter::<BE, _>::new(MemWordWriterVec::new(&mut buffer));

            writer.write_all(&data[..i]).unwrap();
            std::io::Write::flush(&mut writer).unwrap();

            let buffer = writer.into_inner().unwrap().into_inner();
            assert_eq!(unsafe { &buffer.align_to::<u8>().1[..i] }, &data[..i]);

            let mut buffer = Vec::<u64>::new();
            let mut writer = BufBitWriter::<LE, _>::new(MemWordWriterVec::new(&mut buffer));

            writer.write_all(&data[..i]).unwrap();
            std::io::Write::flush(&mut writer).unwrap();

            let buffer = writer.into_inner().unwrap().into_inner();
            assert_eq!(unsafe { &buffer.align_to::<u8>().1[..i] }, &data[..i]);
        }
    }

    macro_rules! test_buf_bit_writer {
        ($f: ident, $word:ty) => {
            #[test]
            fn $f() -> Result<(), Box<dyn std::error::Error + Send + Sync + 'static>> {
                #[allow(unused_imports)]
                use crate::{
                    codes::{GammaRead, GammaWrite},
                    prelude::{
                        BufBitReader, DeltaRead, DeltaWrite, MemWordReader, len_delta, len_gamma,
                    },
                };
                use rand::Rng;
                use rand::{SeedableRng, rngs::SmallRng};

                let mut buffer_be: Vec<$word> = vec![];
                let mut buffer_le: Vec<$word> = vec![];
                let mut big = BufBitWriter::<BE, _>::new(MemWordWriterVec::new(&mut buffer_be));
                let mut little = BufBitWriter::<LE, _>::new(MemWordWriterVec::new(&mut buffer_le));

                let mut r = SmallRng::seed_from_u64(0);
                const ITER: usize = 1_000_000;

                for _ in 0..ITER {
                    let value = r.random_range(0..128);
                    assert_eq!(big.write_gamma(value)?, len_gamma(value));
                    let value = r.random_range(0..128);
                    assert_eq!(little.write_gamma(value)?, len_gamma(value));
                    let value = r.random_range(0..128);
                    assert_eq!(big.write_gamma(value)?, len_gamma(value));
                    let value = r.random_range(0..128);
                    assert_eq!(little.write_gamma(value)?, len_gamma(value));
                    let value = r.random_range(0..128);
                    assert_eq!(big.write_delta(value)?, len_delta(value));
                    let value = r.random_range(0..128);
                    assert_eq!(little.write_delta(value)?, len_delta(value));
                    let value = r.random_range(0..128);
                    assert_eq!(big.write_delta(value)?, len_delta(value));
                    let value = r.random_range(0..128);
                    assert_eq!(little.write_delta(value)?, len_delta(value));
                    let n_bits = r.random_range(0..=64);
                    if n_bits == 0 {
                        big.write_bits(0, 0)?;
                    } else {
                        big.write_bits(r.random::<u64>() & u64::MAX >> 64 - n_bits, n_bits)?;
                    }
                    let n_bits = r.random_range(0..=64);
                    if n_bits == 0 {
                        little.write_bits(0, 0)?;
                    } else {
                        little.write_bits(r.random::<u64>() & u64::MAX >> 64 - n_bits, n_bits)?;
                    }
                    let value = r.random_range(0..128);
                    assert_eq!(big.write_unary(value)?, value as usize + 1);
                    let value = r.random_range(0..128);
                    assert_eq!(little.write_unary(value)?, value as usize + 1);
                }

                drop(big);
                drop(little);

                type ReadWord = u16;
                #[allow(clippy::size_of_in_element_count)] // false positive
                let be_trans: &[ReadWord] = unsafe {
                    core::slice::from_raw_parts(
                        buffer_be.as_ptr() as *const ReadWord,
                        buffer_be.len()
                            * (core::mem::size_of::<$word>() / core::mem::size_of::<ReadWord>()),
                    )
                };
                #[allow(clippy::size_of_in_element_count)] // false positive
                let le_trans: &[ReadWord] = unsafe {
                    core::slice::from_raw_parts(
                        buffer_le.as_ptr() as *const ReadWord,
                        buffer_le.len()
                            * (core::mem::size_of::<$word>() / core::mem::size_of::<ReadWord>()),
                    )
                };

                let mut big_buff = BufBitReader::<BE, _>::new(MemWordReader::new(be_trans));
                let mut little_buff = BufBitReader::<LE, _>::new(MemWordReader::new(le_trans));

                let mut r = SmallRng::seed_from_u64(0);

                for _ in 0..ITER {
                    assert_eq!(big_buff.read_gamma()?, r.random_range(0..128));
                    assert_eq!(little_buff.read_gamma()?, r.random_range(0..128));
                    assert_eq!(big_buff.read_gamma()?, r.random_range(0..128));
                    assert_eq!(little_buff.read_gamma()?, r.random_range(0..128));
                    assert_eq!(big_buff.read_delta()?, r.random_range(0..128));
                    assert_eq!(little_buff.read_delta()?, r.random_range(0..128));
                    assert_eq!(big_buff.read_delta()?, r.random_range(0..128));
                    assert_eq!(little_buff.read_delta()?, r.random_range(0..128));
                    let n_bits = r.random_range(0..=64);
                    if n_bits == 0 {
                        assert_eq!(big_buff.read_bits(0)?, 0);
                    } else {
                        assert_eq!(
                            big_buff.read_bits(n_bits)?,
                            r.random::<u64>() & u64::MAX >> 64 - n_bits
                        );
                    }
                    let n_bits = r.random_range(0..=64);
                    if n_bits == 0 {
                        assert_eq!(little_buff.read_bits(0)?, 0);
                    } else {
                        assert_eq!(
                            little_buff.read_bits(n_bits)?,
                            r.random::<u64>() & u64::MAX >> 64 - n_bits
                        );
                    }

                    assert_eq!(big_buff.read_unary()?, r.random_range(0..128));
                    assert_eq!(little_buff.read_unary()?, r.random_range(0..128));
                }

                Ok(())
            }
        };
    }

    test_buf_bit_writer!(test_u128, u128);
    test_buf_bit_writer!(test_u64, u64);
    test_buf_bit_writer!(test_u32, u32);

    test_buf_bit_writer!(test_u16, u16);
    test_buf_bit_writer!(test_usize, usize);
}