arrow_buffer/builder/

boolean.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 crate::bit_util::apply_bitwise_binary_op;
use crate::{BooleanBuffer, Buffer, MutableBuffer, bit_util};
use std::ops::Range;

/// Builder for [`BooleanBuffer`]
///
/// # See Also
///
/// * [`NullBuffer`] for building [`BooleanBuffer`]s for representing nulls
///
/// [`NullBuffer`]: crate::NullBuffer
#[derive(Debug)]
pub struct BooleanBufferBuilder {
    buffer: MutableBuffer,
    len: usize,
}

impl BooleanBufferBuilder {
    /// Creates a new `BooleanBufferBuilder` with sufficient space for
    /// `capacity` bits (not bytes).
    ///
    /// The capacity is rounded up to the nearest multiple of 8 for the
    /// allocation.
    #[inline]
    pub fn new(capacity: usize) -> Self {
        let byte_capacity = bit_util::ceil(capacity, 8);
        let buffer = MutableBuffer::new(byte_capacity);
        Self { buffer, len: 0 }
    }

    /// Creates a new `BooleanBufferBuilder` from [`MutableBuffer`] of `len`
    pub fn new_from_buffer(buffer: MutableBuffer, len: usize) -> Self {
        assert!(len <= buffer.len() * 8);
        let mut s = Self {
            len: buffer.len() * 8,
            buffer,
        };
        s.truncate(len);
        s
    }

    /// Returns the length of the buffer
    #[inline]
    pub fn len(&self) -> usize {
        self.len
    }

    /// Sets a bit in the buffer at `index`
    #[inline]
    pub fn set_bit(&mut self, index: usize, v: bool) {
        if v {
            bit_util::set_bit(self.buffer.as_mut(), index);
        } else {
            bit_util::unset_bit(self.buffer.as_mut(), index);
        }
    }

    /// Gets a bit in the buffer at `index`
    #[inline]
    pub fn get_bit(&self, index: usize) -> bool {
        bit_util::get_bit(self.buffer.as_slice(), index)
    }

    /// Returns true if empty
    #[inline]
    pub fn is_empty(&self) -> bool {
        self.len == 0
    }

    /// Returns the capacity of the buffer, in bits (not bytes)
    ///
    /// Note this
    ///
    /// # Example
    /// ```
    /// # use arrow_buffer::builder::BooleanBufferBuilder;
    /// // empty requires 0 bytes
    /// let b = BooleanBufferBuilder::new(0);
    /// assert_eq!(0, b.capacity());
    /// // Creating space for 1 bit results in 64 bytes (space for 512 bits)
    /// // (64 is the minimum allocation size for 64 bit architectures)
    /// let mut b = BooleanBufferBuilder::new(1);
    /// assert_eq!(512, b.capacity());
    /// // 1000 bits requires 128 bytes (space for 1024 bits)
    /// b.append_n(1000, true);
    /// assert_eq!(1024, b.capacity());
    /// ```
    #[inline]
    pub fn capacity(&self) -> usize {
        self.buffer.capacity() * 8
    }

    /// Advances the buffer by `additional` bits
    #[inline]
    pub fn advance(&mut self, additional: usize) {
        let new_len = self.len + additional;
        let new_len_bytes = bit_util::ceil(new_len, 8);
        if new_len_bytes > self.buffer.len() {
            self.buffer.resize(new_len_bytes, 0);
        }
        self.len = new_len;
    }

    /// Truncates the builder to the given length
    ///
    /// If `len` is greater than the buffer's current length, this has no effect
    #[inline]
    pub fn truncate(&mut self, len: usize) {
        if len > self.len {
            return;
        }

        let new_len_bytes = bit_util::ceil(len, 8);
        self.buffer.truncate(new_len_bytes);
        self.len = len;

        let remainder = self.len % 8;
        if remainder != 0 {
            let mask = (1_u8 << remainder).wrapping_sub(1);
            *self.buffer.as_mut().last_mut().unwrap() &= mask;
        }
    }

    /// Reserve space to at least `additional` new bits.
    /// Capacity will be `>= self.len() + additional`.
    /// New bytes are uninitialized and reading them is undefined behavior.
    #[inline]
    pub fn reserve(&mut self, additional: usize) {
        let capacity = self.len + additional;
        if capacity > self.capacity() {
            // convert differential to bytes
            let additional = bit_util::ceil(capacity, 8) - self.buffer.len();
            self.buffer.reserve(additional);
        }
    }

    /// Resizes the buffer, either truncating its contents (with no change in capacity), or
    /// growing it (potentially reallocating it) and writing `false` in the newly available bits.
    #[inline]
    pub fn resize(&mut self, len: usize) {
        match len.checked_sub(self.len) {
            Some(delta) => self.advance(delta),
            None => self.truncate(len),
        }
    }

    /// Appends a boolean `v` into the buffer
    #[inline]
    pub fn append(&mut self, v: bool) {
        self.advance(1);
        if v {
            unsafe { bit_util::set_bit_raw(self.buffer.as_mut_ptr(), self.len - 1) };
        }
    }

    /// Appends n `additional` bits of value `v` into the buffer
    #[inline]
    pub fn append_n(&mut self, additional: usize, v: bool) {
        match v {
            true => {
                let new_len = self.len + additional;
                let new_len_bytes = bit_util::ceil(new_len, 8);
                let cur_remainder = self.len % 8;
                let new_remainder = new_len % 8;

                if cur_remainder != 0 {
                    // Pad last byte with 1s
                    *self.buffer.as_slice_mut().last_mut().unwrap() |= !((1 << cur_remainder) - 1)
                }
                self.buffer.resize(new_len_bytes, 0xFF);
                if new_remainder != 0 {
                    // Clear remaining bits
                    *self.buffer.as_slice_mut().last_mut().unwrap() &= (1 << new_remainder) - 1
                }
                self.len = new_len;
            }
            false => self.advance(additional),
        }
    }

    /// Appends a slice of booleans into the buffer
    #[inline]
    pub fn append_slice(&mut self, slice: &[bool]) {
        let additional = slice.len();
        self.advance(additional);

        let offset = self.len() - additional;
        for (i, v) in slice.iter().enumerate() {
            if *v {
                unsafe { bit_util::set_bit_raw(self.buffer.as_mut_ptr(), offset + i) }
            }
        }
    }

    /// Append `range` bits from `to_set`
    ///
    /// `to_set` is a slice of bits packed LSB-first into `[u8]`
    ///
    /// # Panics
    ///
    /// Panics if `to_set` does not contain `ceil(range.end / 8)` bytes
    pub fn append_packed_range(&mut self, range: Range<usize>, to_set: &[u8]) {
        let offset_write = self.len;
        let len = range.end - range.start;
        // allocate new bits as 0
        self.advance(len);
        // copy bits from to_set into self.buffer a word at a time
        apply_bitwise_binary_op(
            self.buffer.as_slice_mut(),
            offset_write,
            to_set,
            range.start,
            len,
            |_a, b| b, // copy bits from to_set
        );
    }

    /// Append [`BooleanBuffer`] to this [`BooleanBufferBuilder`]
    pub fn append_buffer(&mut self, buffer: &BooleanBuffer) {
        let range = buffer.offset()..buffer.offset() + buffer.len();
        self.append_packed_range(range, buffer.values())
    }

    /// Returns the packed bits
    pub fn as_slice(&self) -> &[u8] {
        self.buffer.as_slice()
    }

    /// Returns the packed bits
    pub fn as_slice_mut(&mut self) -> &mut [u8] {
        self.buffer.as_slice_mut()
    }

    /// Creates a [`BooleanBuffer`]
    #[inline]
    pub fn finish(&mut self) -> BooleanBuffer {
        let buf = std::mem::replace(&mut self.buffer, MutableBuffer::new(0));
        let len = std::mem::replace(&mut self.len, 0);
        BooleanBuffer::new(buf.into(), 0, len)
    }

    /// Builds the [BooleanBuffer] without resetting the builder.
    pub fn finish_cloned(&self) -> BooleanBuffer {
        BooleanBuffer::new(Buffer::from_slice_ref(self.as_slice()), 0, self.len)
    }
}

impl From<BooleanBufferBuilder> for Buffer {
    #[inline]
    fn from(builder: BooleanBufferBuilder) -> Self {
        builder.buffer.into()
    }
}

impl From<BooleanBufferBuilder> for BooleanBuffer {
    #[inline]
    fn from(builder: BooleanBufferBuilder) -> Self {
        BooleanBuffer::new(builder.buffer.into(), 0, builder.len)
    }
}

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

    #[test]
    fn test_boolean_buffer_builder_write_bytes() {
        let mut b = BooleanBufferBuilder::new(4);
        b.append(false);
        b.append(true);
        b.append(false);
        b.append(true);
        assert_eq!(4, b.len());
        assert_eq!(512, b.capacity());
        let buffer = b.finish();
        assert_eq!(4, buffer.len());

        // Overallocate capacity
        let mut b = BooleanBufferBuilder::new(8);
        b.append_slice(&[false, true, false, true]);
        assert_eq!(4, b.len());
        assert_eq!(512, b.capacity());
        let buffer = b.finish();
        assert_eq!(4, buffer.len());
    }

    #[test]
    fn test_boolean_buffer_builder_unset_first_bit() {
        let mut buffer = BooleanBufferBuilder::new(4);
        buffer.append(true);
        buffer.append(true);
        buffer.append(false);
        buffer.append(true);
        buffer.set_bit(0, false);
        assert_eq!(buffer.len(), 4);
        assert_eq!(buffer.finish().values(), &[0b1010_u8]);
    }

    #[test]
    fn test_boolean_buffer_builder_unset_last_bit() {
        let mut buffer = BooleanBufferBuilder::new(4);
        buffer.append(true);
        buffer.append(true);
        buffer.append(false);
        buffer.append(true);
        buffer.set_bit(3, false);
        assert_eq!(buffer.len(), 4);
        assert_eq!(buffer.finish().values(), &[0b0011_u8]);
    }

    #[test]
    fn test_boolean_buffer_builder_unset_an_inner_bit() {
        let mut buffer = BooleanBufferBuilder::new(5);
        buffer.append(true);
        buffer.append(true);
        buffer.append(false);
        buffer.append(true);
        buffer.set_bit(1, false);
        assert_eq!(buffer.len(), 4);
        assert_eq!(buffer.finish().values(), &[0b1001_u8]);
    }

    #[test]
    fn test_boolean_buffer_builder_unset_several_bits() {
        let mut buffer = BooleanBufferBuilder::new(5);
        buffer.append(true);
        buffer.append(true);
        buffer.append(true);
        buffer.append(false);
        buffer.append(true);
        buffer.set_bit(1, false);
        buffer.set_bit(2, false);
        assert_eq!(buffer.len(), 5);
        assert_eq!(buffer.finish().values(), &[0b10001_u8]);
    }

    #[test]
    fn test_boolean_buffer_builder_unset_several_bits_bigger_than_one_byte() {
        let mut buffer = BooleanBufferBuilder::new(16);
        buffer.append_n(10, true);
        buffer.set_bit(0, false);
        buffer.set_bit(3, false);
        buffer.set_bit(9, false);
        assert_eq!(buffer.len(), 10);
        assert_eq!(buffer.finish().values(), &[0b11110110_u8, 0b01_u8]);
    }

    #[test]
    fn test_boolean_buffer_builder_flip_several_bits_bigger_than_one_byte() {
        let mut buffer = BooleanBufferBuilder::new(16);
        buffer.append_n(5, true);
        buffer.append_n(5, false);
        buffer.append_n(5, true);
        buffer.set_bit(0, false);
        buffer.set_bit(3, false);
        buffer.set_bit(9, false);
        buffer.set_bit(6, true);
        buffer.set_bit(14, true);
        buffer.set_bit(13, false);
        assert_eq!(buffer.len(), 15);
        assert_eq!(buffer.finish().values(), &[0b01010110_u8, 0b1011100_u8]);
    }

    #[test]
    fn test_bool_buffer_builder_get_first_bit() {
        let mut buffer = BooleanBufferBuilder::new(16);
        buffer.append_n(8, true);
        buffer.append_n(8, false);
        assert!(buffer.get_bit(0));
    }

    #[test]
    fn test_bool_buffer_builder_get_first_bit_not_requires_mutability() {
        let buffer = {
            let mut buffer = BooleanBufferBuilder::new(16);
            buffer.append_n(8, true);
            buffer
        };

        assert!(buffer.get_bit(0));
    }

    #[test]
    fn test_bool_buffer_builder_get_last_bit() {
        let mut buffer = BooleanBufferBuilder::new(16);
        buffer.append_n(8, true);
        buffer.append_n(8, false);
        assert!(!buffer.get_bit(15));
    }

    #[test]
    fn test_bool_buffer_builder_get_an_inner_bit() {
        let mut buffer = BooleanBufferBuilder::new(16);
        buffer.append_n(4, false);
        buffer.append_n(8, true);
        buffer.append_n(4, false);
        assert!(buffer.get_bit(11));
    }

    #[test]
    fn test_bool_buffer_fuzz() {
        use rand::prelude::*;

        let mut buffer = BooleanBufferBuilder::new(12);
        let mut all_bools = vec![];
        let mut rng = rand::rng();

        let src_len = 32;
        let (src, compacted_src) = {
            let src: Vec<_> = std::iter::from_fn(|| Some(rng.next_u32() & 1 == 0))
                .take(src_len)
                .collect();

            let mut compacted_src = BooleanBufferBuilder::new(src_len);
            compacted_src.append_slice(&src);
            (src, compacted_src.finish())
        };

        for _ in 0..100 {
            let a = rng.next_u32() as usize % src_len;
            let b = rng.next_u32() as usize % src_len;

            let start = a.min(b);
            let end = a.max(b);

            buffer.append_packed_range(start..end, compacted_src.values());
            all_bools.extend_from_slice(&src[start..end]);
        }

        let mut compacted = BooleanBufferBuilder::new(all_bools.len());
        compacted.append_slice(&all_bools);

        assert_eq!(buffer.finish(), compacted.finish())
    }

    #[test]
    fn test_boolean_array_builder_resize() {
        let mut builder = BooleanBufferBuilder::new(20);
        builder.append_n(4, true);
        builder.append_n(7, false);
        builder.append_n(2, true);
        builder.resize(20);

        assert_eq!(builder.len(), 20);
        assert_eq!(builder.as_slice(), &[0b00001111, 0b00011000, 0b00000000]);

        builder.resize(5);
        assert_eq!(builder.len(), 5);
        assert_eq!(builder.as_slice(), &[0b00001111]);

        builder.append_n(4, true);
        assert_eq!(builder.len(), 9);
        assert_eq!(builder.as_slice(), &[0b11101111, 0b00000001]);
    }

    #[test]
    fn test_truncate() {
        let b = MutableBuffer::from_iter([true, true, true, true]);
        let mut builder = BooleanBufferBuilder::new_from_buffer(b, 2);
        builder.advance(2);
        let finished = builder.finish();
        assert_eq!(finished.values(), &[0b00000011]);

        let mut builder = BooleanBufferBuilder::new(10);
        builder.append_n(5, true);
        builder.resize(3);
        builder.advance(2);
        let finished = builder.finish();
        assert_eq!(finished.values(), &[0b00000111]);

        let mut builder = BooleanBufferBuilder::new(10);
        builder.append_n(16, true);
        assert_eq!(builder.as_slice(), &[0xFF, 0xFF]);
        builder.truncate(20);
        assert_eq!(builder.as_slice(), &[0xFF, 0xFF]);
        builder.truncate(14);
        assert_eq!(builder.as_slice(), &[0xFF, 0b00111111]);
        builder.append(false);
        builder.append(true);
        assert_eq!(builder.as_slice(), &[0xFF, 0b10111111]);
        builder.append_packed_range(0..3, &[0xFF]);
        assert_eq!(builder.as_slice(), &[0xFF, 0b10111111, 0b00000111]);
        builder.truncate(17);
        assert_eq!(builder.as_slice(), &[0xFF, 0b10111111, 0b00000001]);
        builder.append_packed_range(0..2, &[2]);
        assert_eq!(builder.as_slice(), &[0xFF, 0b10111111, 0b0000101]);
        builder.truncate(8);
        assert_eq!(builder.as_slice(), &[0xFF]);
        builder.resize(14);
        assert_eq!(builder.as_slice(), &[0xFF, 0x00]);
        builder.truncate(0);
        assert_eq!(builder.as_slice(), &[]);
    }

    #[test]
    fn test_boolean_builder_increases_buffer_len() {
        // 00000010 01001000
        let buf = Buffer::from([72_u8, 2_u8]);
        let mut builder = BooleanBufferBuilder::new(8);

        for i in 0..16 {
            if i == 3 || i == 6 || i == 9 {
                builder.append(true);
            } else {
                builder.append(false);
            }
        }
        let buf2 = builder.finish();

        assert_eq!(buf.len(), buf2.inner().len());
        assert_eq!(buf.as_slice(), buf2.values());
    }
}