golang/go

regexp: Scan the input string backward for patterns ending in $

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#21,743 opened on Sep 2, 2017

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 (4 comments) (1 reaction) (0 assignees)Go (19,008 forks)batch import
NeedsFixPerformancehelp wanted

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Description

As suggested by @rsc:

It seems clear that we should handle patterns ending in $, like \.(jpe?g|gif)$, by scanning the string backward, which cuts the processing from O(n) to O(1) for an input of size n. That's easy to add to the existing matchers and doesn't need to be limited to fixed-size patterns.

I'm working on a CL to implement it for strings and byte slices.

Contributor guide

Research direction
Study the existing regexp matcher code for string and byte slice matching to understand how to implement backward scanning for patterns ending with $.
Tech stack
go
Domain
backend
Issue type
Feature
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
2
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
1-3 hours
Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.
Active
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
Clear
Prerequisites
Go
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
65