Cord/crates/cord-sparse/src/vector.rs

use crate::index::BoundedSumIter;

/// Multi-dimensional vector indexed by a bounded-sum multi-index set.
///
/// Storage is split by first dimension for cache-friendly access
/// during the unidirectional matrix-vector products: data[i] contains
/// all entries whose multi-index starts with i, in lexicographic order.
///
/// Values are i64 fixed-point throughout.
#[derive(Debug, Clone)]
pub struct MultiDimVec {
    pub data: Vec<Vec<i64>>,
    iter: BoundedSumIter,
}

impl MultiDimVec {
    pub fn new(iter: BoundedSumIter) -> Self {
        let sizes = iter.num_values_per_first_index();
        let data = sizes.iter().map(|&s| vec![0i64; s]).collect();
        Self { data, iter }
    }

    pub fn iter(&self) -> &BoundedSumIter {
        &self.iter
    }

    pub fn reset_with_iter(&mut self, iter: BoundedSumIter) {
        if self.iter.dim() == iter.dim()
            && self.iter.first_index_bound() == iter.first_index_bound()
        {
            self.iter = iter;
            return;
        }
        let sizes = iter.num_values_per_first_index();
        self.data.resize(sizes.len(), Vec::new());
        for (i, &s) in sizes.iter().enumerate() {
            self.data[i].resize(s, 0);
        }
        self.iter = iter;
    }

    pub fn swap(&mut self, other: &mut MultiDimVec) {
        std::mem::swap(&mut self.data, &mut other.data);
        std::mem::swap(&mut self.iter, &mut other.iter);
    }

    pub fn add_assign(&mut self, other: &MultiDimVec) {
        for (row, other_row) in self.data.iter_mut().zip(other.data.iter()) {
            for (a, b) in row.iter_mut().zip(other_row.iter()) {
                *a += b;
            }
        }
    }

    pub fn sub_assign(&mut self, other: &MultiDimVec) {
        for (row, other_row) in self.data.iter_mut().zip(other.data.iter()) {
            for (a, b) in row.iter_mut().zip(other_row.iter()) {
                *a -= b;
            }
        }
    }

    pub fn squared_l2_norm(&self) -> i128 {
        let mut sum: i128 = 0;
        for row in &self.data {
            for &v in row {
                sum += (v as i128) * (v as i128);
            }
        }
        sum
    }
}

/// Iterate over all entries yielding (multi_index, &value).
pub struct MultiDimVecIter<'a> {
    vec: &'a MultiDimVec,
    jump: BoundedSumIter,
    last_dim_idx: usize,
    last_dim_count: usize,
    first_idx: usize,
    tail_counter: usize,
}

impl<'a> MultiDimVecIter<'a> {
    pub fn new(vec: &'a MultiDimVec) -> Self {
        let mut jump = vec.iter.clone();
        jump.reset();
        let count = if jump.valid() { jump.last_dim_count() } else { 0 };
        Self {
            vec,
            jump,
            last_dim_idx: 0,
            last_dim_count: count,
            first_idx: 0,
            tail_counter: 0,
        }
    }
}

impl<'a> Iterator for MultiDimVecIter<'a> {
    type Item = i64;

    fn next(&mut self) -> Option<i64> {
        if !self.jump.valid() {
            return None;
        }

        let val = self.vec.data[self.first_idx][self.tail_counter];
        self.last_dim_idx += 1;
        self.tail_counter += 1;

        if self.last_dim_idx >= self.last_dim_count {
            self.last_dim_idx = 0;
            self.jump.next();
            if self.jump.valid() {
                let new_first = self.jump.first_index();
                if new_first != self.first_idx {
                    self.first_idx = new_first;
                    self.tail_counter = 0;
                }
                self.last_dim_count = self.jump.last_dim_count();
            }
        }

        Some(val)
    }
}

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

    #[test]
    fn storage_size() {
        let it = BoundedSumIter::new(3, 2);
        let v = MultiDimVec::new(it.clone());
        let total: usize = v.data.iter().map(|r| r.len()).sum();
        assert_eq!(total, it.num_values());
    }

    #[test]
    fn iter_all_values() {
        let it = BoundedSumIter::new(3, 2);
        let mut v = MultiDimVec::new(it.clone());
        // Fill with sequential values
        let mut val = 1i64;
        for row in &mut v.data {
            for cell in row.iter_mut() {
                *cell = val;
                val += 1;
            }
        }
        let collected: Vec<i64> = MultiDimVecIter::new(&v).collect();
        assert_eq!(collected.len(), it.num_values());
        assert_eq!(collected[0], 1);
    }
}