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use std::ops;

pub fn slice_range<R>(range: R, bounds: ops::RangeTo<usize>) -> ops::Range<usize>
where
    R: ops::RangeBounds<usize>,
{
    let len = bounds.end;

    let start: ops::Bound<&usize> = range.start_bound();
    let start = match start {
        ops::Bound::Included(&start) => start,
        ops::Bound::Excluded(start) => start
            .checked_add(1)
            .expect("attempted to index slice from after maximum usize"),
        ops::Bound::Unbounded => 0,
    };

    let end: ops::Bound<&usize> = range.end_bound();
    let end = match end {
        ops::Bound::Included(end) => end
            .checked_add(1)
            .expect("attempted to index slice up to maximum usize"),
        ops::Bound::Excluded(&end) => end,
        ops::Bound::Unbounded => len,
    };

    if start > end {
        panic!("slice index starts at {start} but ends at {end}");
    }
    if end > len {
        panic!("range end index {end} out of range for slice of length {len}");
    }

    ops::Range { start, end }
}