rlst 0.9.0

A Rust native linear algebra library.
Documentation 
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//! Helper functions for working with array layouts.
//!
//! The default layout is a column-major format such that in an
//! index `[a0, a1, a2, ...]` the left-most axis is stored consecutively in memory.

/// Compute a column major stride from a shape.
///
/// Given an array shape, compute the corresponding stride assuming column-major ordering.
#[inline(always)]
pub fn col_major_stride_from_shape<const NDIM: usize>(shape: [usize; NDIM]) -> [usize; NDIM] {
    let mut output = [0; NDIM];

    let mut state = 1;
    for (elem, s) in output.iter_mut().zip(shape.iter()) {
        *elem = state;
        state *= s;
    }
    output
}

/// Compute a row major stride from a shape.
///
/// Given an array shape, compute the corresponding stride assuming row-major ordering.
#[inline(always)]
pub fn row_major_stride_from_shape<const NDIM: usize>(shape: [usize; NDIM]) -> [usize; NDIM] {
    let mut output = [0; NDIM];

    let mut state = 1;
    for (elem, s) in output.iter_mut().zip(shape.iter()).rev() {
        *elem = state;
        state *= s;
    }
    output
}

/// Return true if `multi_index` in bounds with respect to `shape`.
#[inline(always)]
pub fn check_multi_index_in_bounds<const N: usize>(
    multi_index: [usize; N],
    shape: [usize; N],
) -> bool {
    for (ind, s) in multi_index.iter().zip(shape.iter()) {
        if ind >= s {
            return false;
        }
    }
    true
}

/// Convert a multi-index into a 1d index.
#[inline(always)]
pub fn convert_nd_raw<const NDIM: usize>(
    multi_index: [usize; NDIM],
    stride: [usize; NDIM],
) -> usize {
    let mut acc = 0;

    for ind in 0..NDIM {
        acc += multi_index[ind] * stride[ind];
    }

    acc
}

/// Convert a 1d index into a multi-index assuming column major ordering.
#[inline(always)]
pub fn convert_1d_nd_from_shape<const NDIM: usize>(
    mut index: usize,
    shape: [usize; NDIM],
) -> [usize; NDIM] {
    let mut res = [0; NDIM];
    debug_assert!(index < shape.iter().product());
    for ind in 0..NDIM {
        res[ind] = index % shape[ind];
        index /= shape[ind];
    }
    res
}

#[cfg(test)]
mod test {

    use super::*;

    #[test]
    fn test_col_major_stride_from_shape() {
        let shape = [2, 5, 4];
        let expected = [1, 2, 10];

        assert_eq!(expected, col_major_stride_from_shape(shape));
    }

    #[test]
    fn test_row_major_stride_from_shape() {
        let shape = [2, 5, 4];
        let expected = [20, 4, 1];

        assert_eq!(expected, row_major_stride_from_shape(shape));
    }

    #[test]
    fn test_convert_nd_raw() {
        let multi_index = [1, 3, 2];
        let stride = [1, 3, 6];

        assert_eq!(22, convert_nd_raw(multi_index, stride))
    }

    #[test]
    fn test_convert_1d_nd() {
        let index = 15;

        let shape = [8, 2];

        assert_eq!([7, 1], convert_1d_nd_from_shape(index, shape))
    }
}