hwt 0.4.2

Hamming Weight Tree for finding neighbors in Hamming space
Documentation 
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use crate::search::*;
use swar::*;

/// Gets all the possible offsets in a feature that maintain a particular
/// exact radius.
///
/// - `sp` - Search parent CHF<6>
/// - `sc` - Search child CHF<7>
/// - `tp` - Target parent CHF<6>
///
/// Returns an iterator over the `tc` (target children).
pub fn search_exact128(
    bits: u32,
    sp: Bits2<u128>,
    sc: Bits1<u128>,
    tp: Bits2<u128>,
    radius: u32,
) -> impl Iterator<Item = Bits1<u128>> {
    let (lsp, rsp) = sp.halve();
    let (lsc, rsc) = sc.halve();
    let (ltp, rtp) = tp.halve();

    Box::new(
        search_radius64(bits, lsp, lsc, ltp, radius).flat_map(move |(ltc, lsod)| {
            search_exact64(bits, rsp, rsc, rtp, radius - lsod)
                .map(move |rtc| Bits1::union(ltc, rtc))
        }),
    )
}

/// Gets all the possible offsets in a feature that maintain a particular
/// exact radius.
///
/// - `sp` - Search parent CHF<5>
/// - `sc` - Search child CHF<6>
/// - `tp` - Target parent CHF<5>
///
/// Returns an iterator over the `tc` (target children).
pub fn search_exact64(
    bits: u32,
    sp: Bits4<u128>,
    sc: Bits2<u128>,
    tp: Bits4<u128>,
    radius: u32,
) -> impl Iterator<Item = Bits2<u128>> {
    let (lsp, rsp) = sp.halve();
    let (lsc, rsc) = sc.halve();
    let (ltp, rtp) = tp.halve();

    Box::new(
        search_radius32(bits, lsp, lsc, ltp, radius).flat_map(move |(ltc, lsod)| {
            search_exact32(bits, rsp, rsc, rtp, radius - lsod)
                .map(move |rtc| Bits2::union(ltc, rtc))
        }),
    )
}

/// Gets all the possible offsets in a feature that maintain a particular
/// exact radius.
///
/// - `sp` - Search parent CHF<4>
/// - `sc` - Search child CHF<5>
/// - `tp` - Target parent CHF<4>
///
/// Returns an iterator over the `tc` (target children).
pub fn search_exact32(
    bits: u32,
    sp: Bits8<u128>,
    sc: Bits4<u128>,
    tp: Bits8<u128>,
    radius: u32,
) -> impl Iterator<Item = Bits4<u128>> {
    let (lsp, rsp) = sp.halve();
    let (lsc, rsc) = sc.halve();
    let (ltp, rtp) = tp.halve();

    Box::new(
        search_radius16(bits, lsp, lsc, ltp, radius).flat_map(move |(ltc, lsod)| {
            search_exact16(bits, rsp, rsc, rtp, radius - lsod)
                .map(move |rtc| Bits4::union(ltc, rtc))
        }),
    )
}

/// Gets all the possible offsets in a feature that maintain a particular
/// exact radius.
///
/// - `sp` - Search parent CHF<3>
/// - `sc` - Search child CHF<4>
/// - `tp` - Target parent CHF<3>
///
/// Returns an iterator over the `tc` (target children).
pub fn search_exact16(
    bits: u32,
    sp: Bits16<u128>,
    sc: Bits8<u128>,
    tp: Bits16<u128>,
    radius: u32,
) -> impl Iterator<Item = Bits8<u128>> {
    let (lsp, rsp) = sp.halve();
    let (lsc, rsc) = sc.halve();
    let (ltp, rtp) = tp.halve();

    Box::new(
        search_radius8(bits, lsp, lsc, ltp, radius).flat_map(move |(ltc, lsod)| {
            search_exact8(bits, rsp, rsc, rtp, radius - lsod).map(move |rtc| Bits8::union(ltc, rtc))
        }),
    )
}

/// Gets all the possible offsets in a feature that maintain a particular
/// exact radius.
///
/// - `sp` - Search parent CHF<2>
/// - `sc` - Search child CHF<3>
/// - `tp` - Target parent CHF<2>
///
/// Returns an iterator over the `tc` (target children).
pub fn search_exact8(
    bits: u32,
    sp: Bits32<u128>,
    sc: Bits16<u128>,
    tp: Bits32<u128>,
    radius: u32,
) -> impl Iterator<Item = Bits16<u128>> {
    let (lsp, rsp) = sp.halve();
    let (lsc, rsc) = sc.halve();
    let (ltp, rtp) = tp.halve();

    search_radius4(bits, lsp, lsc, ltp, radius).flat_map(move |(ltc, lsod)| {
        search_exact4(bits, rsp, rsc, rtp, radius - lsod).map(move |rtc| Bits16::union(ltc, rtc))
    })
}

/// Gets all the possible offsets in a feature that maintain a particular
/// exact radius.
///
/// - `sp` - Search parent CHF<1>
/// - `sc` - Search child CHF<2>
/// - `tp` - Target parent CHF<1>
///
/// Returns an iterator over the `tc` (target children).
pub fn search_exact4(
    bits: u32,
    sp: Bits64<u128>,
    sc: Bits32<u128>,
    tp: Bits64<u128>,
    radius: u32,
) -> impl Iterator<Item = Bits32<u128>> {
    let (lsp, rsp) = sp.halve();
    let (lsc, rsc) = sc.halve();
    let (ltp, rtp) = tp.halve();

    search_radius2(bits, lsp, lsc, ltp, radius).flat_map(move |(ltc, lsod)| {
        search_exact2(bits, rsp, rsc, rtp, radius - lsod).map(move |rtc| Bits32::union(ltc, rtc))
    })
}

/// Gets all the possible offsets in a feature that maintain a particular
/// exact radius.
///
/// - `sp` - Search parent CHF<0>
/// - `sc` - Search child CHF<1>
/// - `tp` - Target parent CHF<0>
///
/// Returns an iterator over the `tc` target children at that radius.
pub fn search_exact2(
    bits: u32,
    sp: Bits128<u128>,
    sc: Bits64<u128>,
    tp: Bits128<u128>,
    radius: u32,
) -> impl Iterator<Item = Bits64<u128>> {
    // Get the number of ones in the search word.
    let sw = sp.count_ones();
    // Get the number of ones in the left half.
    let sl = (sc >> 64).count_ones();
    // Get the number of ones in the target word.
    let tw = tp.count_ones();

    search_exact(bits, sl, sw, tw, radius)
        .map(|[tl, tr]| Bits64(((1 << tl) - 1) << 64 | ((1 << tr) - 1)))
}

/// Iterator over the indices that fall within a radius of a number.
///
/// - `bits` - The number of bits that make up the bit substring `sl`
///     comes from.
/// - `sl` - The weight of the left half of the search number.
/// - `sw` - The weight of the whole search number.
/// - `tw` - The weight of the whole target number.
/// - `radius` - The exact sum of distances (sod) of matches.
///
/// Returns the iterator over (tl, tr).
pub fn search_exact(
    bits: u32,
    sl: u32,
    sw: u32,
    tw: u32,
    radius: u32,
) -> impl Iterator<Item = [u32; 2]> {
    // This function uses things derived in the Search section in the crate
    // documentation. Read that before messing with this code.

    // Compute the `max` and `min` for `tl` range.
    let max = std::cmp::min(tw, bits);
    let min = tw - max;

    let filter = move |&tl: &i32| tl >= min as i32 && tl <= max as i32;

    // We do a lot of signed operations and sometimes compute negative numbers.
    // It is easier to change these to `i32` now.
    let sl = sl as i32;
    let sw = sw as i32;
    let tw = tw as i32;
    let radius = radius as i32;

    // See crate documentation on what `C` is.
    let c = 2 * sl - sw + tw;

    let bottom_distance = (tw - sw).abs();

    let map = move |tl| [tl as u32, (tw - tl) as u32];

    if bottom_distance == radius {
        // We intersect at the flat bottom, so get the inflection points
        // and use them to create the flat range.
        let inflection1 = sl;
        let inflection2 = tw - (sw - sl);
        let min_inflection = std::cmp::min(inflection1, inflection2);
        let max_inflection = std::cmp::max(inflection1, inflection2);
        either::Left(min_inflection..=max_inflection)
            .filter(filter)
            .map(map)
    } else if bottom_distance < radius {
        // We intersect at precisely two locations.
        let start = (-radius + c + 1) / 2;
        let end = (radius + c) / 2;

        either::Right(std::iter::once(start).chain(std::iter::once(end)))
            .filter(filter)
            .map(map)
    } else {
        // Create fake iterators to satisfy the type system.
        let flat = 0..=-1;

        // Also perform the same operations over here.
        either::Left(flat).filter(filter).map(map)
    }
}