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Diffstat (limited to 'vendor/smawk/src/monge.rs')
-rw-r--r-- | vendor/smawk/src/monge.rs | 121 |
1 files changed, 0 insertions, 121 deletions
diff --git a/vendor/smawk/src/monge.rs b/vendor/smawk/src/monge.rs deleted file mode 100644 index dbc80e1..0000000 --- a/vendor/smawk/src/monge.rs +++ /dev/null @@ -1,121 +0,0 @@ -//! Functions for generating and checking Monge arrays. -//! -//! The functions here are mostly meant to be used for testing -//! correctness of the SMAWK implementation. - -use crate::Matrix; -use std::num::Wrapping; -use std::ops::Add; - -/// Verify that a matrix is a Monge matrix. -/// -/// A [Monge matrix] \(or array) is a matrix where the following -/// inequality holds: -/// -/// ```text -/// M[i, j] + M[i', j'] <= M[i, j'] + M[i', j] for all i < i', j < j' -/// ``` -/// -/// The inequality says that the sum of the main diagonal is less than -/// the sum of the antidiagonal. Checking this condition is done by -/// checking *n* ✕ *m* submatrices, so the running time is O(*mn*). -/// -/// [Monge matrix]: https://en.wikipedia.org/wiki/Monge_array -pub fn is_monge<T: Ord + Copy, M: Matrix<T>>(matrix: &M) -> bool -where - Wrapping<T>: Add<Output = Wrapping<T>>, -{ - /// Returns `Ok(a + b)` if the computation can be done without - /// overflow, otherwise `Err(a + b - T::MAX - 1)` is returned. - fn checked_add<T: Ord + Copy>(a: Wrapping<T>, b: Wrapping<T>) -> Result<T, T> - where - Wrapping<T>: Add<Output = Wrapping<T>>, - { - let sum = a + b; - if sum < a { - Err(sum.0) - } else { - Ok(sum.0) - } - } - - (0..matrix.nrows() - 1) - .flat_map(|row| (0..matrix.ncols() - 1).map(move |col| (row, col))) - .all(|(row, col)| { - let top_left = Wrapping(matrix.index(row, col)); - let top_right = Wrapping(matrix.index(row, col + 1)); - let bot_left = Wrapping(matrix.index(row + 1, col)); - let bot_right = Wrapping(matrix.index(row + 1, col + 1)); - - match ( - checked_add(top_left, bot_right), - checked_add(bot_left, top_right), - ) { - (Ok(a), Ok(b)) => a <= b, // No overflow. - (Err(a), Err(b)) => a <= b, // Double overflow. - (Ok(_), Err(_)) => true, // Anti-diagonal overflow. - (Err(_), Ok(_)) => false, // Main diagonal overflow. - } - }) -} - -#[cfg(test)] -mod tests { - use super::*; - - #[test] - fn is_monge_handles_overflow() { - // The x + y <= z + w computations will overflow for an u8 - // matrix unless is_monge is careful. - let matrix: Vec<Vec<u8>> = vec![ - vec![200, 200, 200, 200], - vec![200, 200, 200, 200], - vec![200, 200, 200, 200], - ]; - assert!(is_monge(&matrix)); - } - - #[test] - fn monge_constant_rows() { - let matrix = vec![ - vec![42, 42, 42, 42], - vec![0, 0, 0, 0], - vec![100, 100, 100, 100], - vec![1000, 1000, 1000, 1000], - ]; - assert!(is_monge(&matrix)); - } - - #[test] - fn monge_constant_cols() { - let matrix = vec![ - vec![42, 0, 100, 1000], - vec![42, 0, 100, 1000], - vec![42, 0, 100, 1000], - vec![42, 0, 100, 1000], - ]; - assert!(is_monge(&matrix)); - } - - #[test] - fn monge_upper_right() { - let matrix = vec![ - vec![10, 10, 42, 42, 42], - vec![10, 10, 42, 42, 42], - vec![10, 10, 10, 10, 10], - vec![10, 10, 10, 10, 10], - ]; - assert!(is_monge(&matrix)); - } - - #[test] - fn monge_lower_left() { - let matrix = vec![ - vec![10, 10, 10, 10, 10], - vec![10, 10, 10, 10, 10], - vec![42, 42, 42, 10, 10], - vec![42, 42, 42, 10, 10], - ]; - assert!(is_monge(&matrix)); - } -} |