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BitParallelEditDistance.Distance

The edit distance from one pattern to every string in a resident batch.

public int[] Distance(string pattern, DeviceTextBlock texts)

Parameters — pattern is the string the batch was renamed against, between 1 and 64 characters. texts is that resident batch.

Returns — int[], one distance per string, in the batch's own order.

Exceptions — ArgumentNullException when an argument is null; ArgumentException when the pattern is empty or longer than 64, or when the batch was renamed against a different alphabet.

Example — the shape a caller writes.

using Lodestar.Gpu.Compute;

using var context = GpuContext.Create(preferCpu: true);
using var block = DeviceTextBlock.Upload(context, "abc", ["abc", "abd", "xyz"]);

int[] distances = new BitParallelEditDistance(context).Distance("abc", block);

int exact = distances[0];  // => 0
int oneEdit = distances[1];  // => 1

Remarks — a global edit distance, not an approximate search. The difference is one bit: the horizontal carry shifts in a trailing 1, which is the boundary condition making the first row of the dynamic program grow with the text. Without it the text may begin anywhere, and the two agree often enough that the defect reads as a rounding — measured, a pattern of "aaaa" against a text of "aaa" answered 0 where the answer is 1.

The equality table is built on the host from the pattern and uploaded per call: 256 entries, which is negligible beside the batch. The batch is what must not be re-uploaded — see DeviceTextBlock for what that costs.

A pattern holding a character the batch's alphabet never saw is refused, not silently treated as unmatched.

Applies to — net10.0, netstandard2.1.

See also — BitParallelEditDistance.