Make is_contiguous check common

[laggui]

Checklist

• Confirmed that run-checks all script has been executed.

Related Issues/PRs

Following this comment in #3077

Changes

Migrated is_contiguous to common (including minor fix).

Testing

Also added a unit test for shape [3, 1] and strides [1, 1] which would previously be marked as not contiguous.

[laggui]

I also think the check could be simplified to

pub fn is_contiguous(shape: &[usize], strides: &[usize]) -> bool {
    if shape.is_empty() {
        return true;
    }

    let mut expected_stride = 1;

    for (&shape, &stride) in shape.iter().zip(strides).rev() {
        if shape == 1 {
            continue;
        }

        if stride != expected_stride {
            return false;
        }

        expected_stride *= shape;
    }

    true
}

But leaving this here as a note and not a required change.

[nathanielsimard]

I would prefer that strategy actually, we could even create a function that could be used to create the strides AND be used for the checks:

pub fn contiguous_strides(shape: &[usize]) -> impl Iterator<Item = usize> {
    let mut current = 1;
    shape
            .iter()
            .rev()
            .map(|val| {
                current *= val;
                current
            })
            .rev()
}

pub fn is_contiguous(shape: &[usize], strides: &[usize]) -> bool { 
    if shape.is_empty() {
         return true;
     }
     
     for (i, expected) in contiguous_strides(shape).enumerate() {
         if expected != strides[i] {
             return false;
         }
     }
     
     true

[laggui]

The double .rev() cancel out for lazy iterator operations. Also, the first computed stride value should be 1.

I changed the suggested contiguous_strides implementation to match these criteria.

[codecov]

Codecov Report

Attention: Patch coverage is 96.42857% with 1 line in your changes missing coverage. Please review.

Project coverage is 81.09%. Comparing base (e096b0c) to head (efa2a5d).
Report is 9 commits behind head on main.

Files with missing lines	Patch %	Lines
crates/burn-common/src/lib.rs	95.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3083      +/-   ##
==========================================
- Coverage   81.16%   81.09%   -0.08%     
==========================================
  Files         815      817       +2     
  Lines      117201   117320     +119     
==========================================
+ Hits        95121    95135      +14     
- Misses      22080    22185     +105     

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[nathanielsimard]

I would prefer that strategy actually, we could even create a function that could be used to create the strides AND be used for the checks:

pub fn contiguous_strides(shape: &[usize]) -> impl Iterator<Item = usize> {
    let mut current = 1;
    shape
            .iter()
            .rev()
            .map(|val| {
                current *= val;
                current
            })
            .rev()
}

pub fn is_contiguous(shape: &[usize], strides: &[usize]) -> bool { 
    if shape.is_empty() {
         return true;
     }
     
     for (i, expected) in contiguous_strides(shape).enumerate() {
         if expected != strides[i] {
             return false;
         }
     }
     
     true