arrow2 0.18.0

// 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::{
    array::PrimitiveArray,
    compute::sort::SortOptions,
    types::{f16, i256, NativeType},
};

use super::{null_sentinel, Rows};

pub trait FromSlice {
    fn from_slice(slice: &[u8], invert: bool) -> Self;
}

impl<const N: usize> FromSlice for [u8; N] {
    #[inline]
    fn from_slice(slice: &[u8], invert: bool) -> Self {
        let mut t: Self = slice.try_into().unwrap();
        if invert {
            t.iter_mut().for_each(|o| *o = !*o);
        }
        t
    }
}

/// Encodes a value of a particular fixed width type into bytes according to the rules
/// described on [`super::RowConverter`]
pub trait FixedLengthEncoding: Copy {
    const ENCODED_LEN: usize = 1 + std::mem::size_of::<Self::Encoded>();

    type Encoded: Sized + Copy + FromSlice + AsRef<[u8]> + AsMut<[u8]>;

    fn encode(self) -> Self::Encoded;

    fn decode(encoded: Self::Encoded) -> Self;
}

impl FixedLengthEncoding for bool {
    type Encoded = [u8; 1];

    fn encode(self) -> [u8; 1] {
        [self as u8]
    }

    fn decode(encoded: Self::Encoded) -> Self {
        encoded[0] != 0
    }
}

macro_rules! encode_signed {
    ($n:expr, $t:ty) => {
        impl FixedLengthEncoding for $t {
            type Encoded = [u8; $n];

            fn encode(self) -> [u8; $n] {
                let mut b = self.to_be_bytes();
                // Toggle top "sign" bit to ensure consistent sort order
                b[0] ^= 0x80;
                b
            }

            fn decode(mut encoded: Self::Encoded) -> Self {
                // Toggle top "sign" bit
                encoded[0] ^= 0x80;
                Self::from_be_bytes(encoded)
            }
        }
    };
}

encode_signed!(1, i8);
encode_signed!(2, i16);
encode_signed!(4, i32);
encode_signed!(8, i64);
encode_signed!(16, i128);
encode_signed!(32, i256);

macro_rules! encode_unsigned {
    ($n:expr, $t:ty) => {
        impl FixedLengthEncoding for $t {
            type Encoded = [u8; $n];

            fn encode(self) -> [u8; $n] {
                self.to_be_bytes()
            }

            fn decode(encoded: Self::Encoded) -> Self {
                Self::from_be_bytes(encoded)
            }
        }
    };
}

encode_unsigned!(1, u8);
encode_unsigned!(2, u16);
encode_unsigned!(4, u32);
encode_unsigned!(8, u64);

impl FixedLengthEncoding for f16 {
    type Encoded = [u8; 2];

    fn encode(self) -> [u8; 2] {
        // https://github.com/rust-lang/rust/blob/9c20b2a8cc7588decb6de25ac6a7912dcef24d65/library/core/src/num/f32.rs#L1176-L1260
        let s = self.to_bits() as i16;
        let val = s ^ (((s >> 15) as u16) >> 1) as i16;
        val.encode()
    }

    fn decode(encoded: Self::Encoded) -> Self {
        let bits = i16::decode(encoded);
        let val = bits ^ (((bits >> 15) as u16) >> 1) as i16;
        Self::from_bits(val as u16)
    }
}

impl FixedLengthEncoding for f32 {
    type Encoded = [u8; 4];

    fn encode(self) -> [u8; 4] {
        // https://github.com/rust-lang/rust/blob/9c20b2a8cc7588decb6de25ac6a7912dcef24d65/library/core/src/num/f32.rs#L1176-L1260
        let s = self.to_bits() as i32;
        let val = s ^ (((s >> 31) as u32) >> 1) as i32;
        val.encode()
    }

    fn decode(encoded: Self::Encoded) -> Self {
        let bits = i32::decode(encoded);
        let val = bits ^ (((bits >> 31) as u32) >> 1) as i32;
        Self::from_bits(val as u32)
    }
}

impl FixedLengthEncoding for f64 {
    type Encoded = [u8; 8];

    fn encode(self) -> [u8; 8] {
        // https://github.com/rust-lang/rust/blob/9c20b2a8cc7588decb6de25ac6a7912dcef24d65/library/core/src/num/f32.rs#L1176-L1260
        let s = self.to_bits() as i64;
        let val = s ^ (((s >> 63) as u64) >> 1) as i64;
        val.encode()
    }

    fn decode(encoded: Self::Encoded) -> Self {
        let bits = i64::decode(encoded);
        let val = bits ^ (((bits >> 63) as u64) >> 1) as i64;
        Self::from_bits(val as u64)
    }
}

/// Returns the total encoded length (including null byte) for a value of type `T::Native`
pub const fn encoded_len<T>(_col: &PrimitiveArray<T>) -> usize
where
    T: NativeType + FixedLengthEncoding,
{
    T::ENCODED_LEN
}

/// Fixed width types are encoded as
///
/// - 1 byte `0` if null or `1` if valid
/// - bytes of [`FixedLengthEncoding`]
pub fn encode<T: FixedLengthEncoding, I: IntoIterator<Item = Option<T>>>(
    out: &mut Rows,
    i: I,
    opts: SortOptions,
) {
    for (offset, maybe_val) in out.offsets.iter_mut().skip(1).zip(i) {
        let end_offset = *offset + T::ENCODED_LEN;
        if let Some(val) = maybe_val {
            let to_write = &mut out.buffer[*offset..end_offset];
            to_write[0] = 1;
            let mut encoded = val.encode();
            if opts.descending {
                // Flip bits to reverse order
                encoded.as_mut().iter_mut().for_each(|v| *v = !*v)
            }
            to_write[1..].copy_from_slice(encoded.as_ref())
        } else {
            out.buffer[*offset] = null_sentinel(opts);
        }
        *offset = end_offset;
    }
}