8000 Improve do_slice by jturner314 · Pull Request #575 · rust-ndarray/ndarray · GitHub
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Merged
bluss merged 2 commits into from
Dec 15, 2018
Merged

Improve do_slice #575

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b953fe5
Specialize do_slice for |step| = 1 case
jturner314 Dec 13, 2018
358c8d9
Prevent overflow when calculating slice stride
jturner314 Dec 13, 2018
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20 changes: 12 additions & 8 deletions src/dimension/mod.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -380,15 +380,19 @@ pub fn do_slice(dim: &mut usize, stride: &mut usize, slice: Slice) -> isize {
offset += stride_offset(m - 1, *stride);
}

let s_prim = s * step;

let d = m / step.abs() as usize;
let r = m % step.abs() as usize;
let m_prim = d + if r > 0 { 1 } else { 0 };
// Update dimension.
let abs_step = step.abs() as usize;
*dim = if abs_step == 1 {
m
} else {
let d = m / abs_step;
let r = m % abs_step;
d + if r > 0 { 1 } else { 0 }
};

// Update dimension and stride coordinate
*dim = m_prim;
*stride = s_prim as usize;
// Update stride. The additional check is necessary to avoid possible
// overflow in the multiplication.
*stride = if *dim <= 1 { 0 } else { (s * step) as usize };

offset
}
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