[API Proposal]: TensorPrimitives.Sequential

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@tannergooding is already working on this.

Since Jan 16, 2025.

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Description

api-suggestion area-System.Numerics.Tensors needs-further-triage
Background and motivation

A common operation initializes a Span/Array with sequential values, e.g. arr[i] == i.
This is something that can be easily vectorized and seems useful even if perf is not critical for the consumer (e.g. it will be a correct implementation of something trivial, but even trivial code sometimes has bugs).

API Proposal

public static void Sequential(Span<int> x, int startValue = 0);
API Usage

var indices = new int[data.Length]
var values = data.Select(x => x.SortKey).ToArray();
TensorPrimitives.Sequential(indices, 0);
MemoryExtensions.Sort(values, indices);
Console.WriteLine($"The first sorted entry has index {indices[0]}");
Alternative Designs

Enumerable.Range() already exists, but it is not very performant/can't work with an already allocated array or span

The method itself could be called Range instead of Sequential.

Risks

Anyone can write a for loop to initialize these spans/arrays or use Enumerable.Range(...).ToArray(). The vectorization gain might be small depending on the context (e.g, sorting in the example above would most likely take a lot more time than what you save on the initialization.

Dominant language
C#
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