{"action":"opened","number":2240,"pull_request":{"url":"https://api.github.com/repos/crystal-lang/crystal/pulls/2240","id":60992913,"html_url":"https://github.com/crystal-lang/crystal/pull/2240","diff_url":"https://github.com/crystal-lang/crystal/pull/2240.diff","patch_url":"https://github.com/crystal-lang/crystal/pull/2240.patch","issue_url":"https://api.github.com/repos/crystal-lang/crystal/issues/2240","number":2240,"state":"open","locked":false,"title":"Primitives: correctly compare signed and unsigned integers. Fixes #571","user":{"login":"asterite","id":209371,"avatar_url":"https://avatars.githubusercontent.com/u/209371?v=3","gravatar_id":"","url":"https://api.github.com/users/asterite","html_url":"https://github.com/asterite","followers_url":"https://api.github.com/users/asterite/followers","following_url":"https://api.github.com/users/asterite/following{/other_user}","gists_url":"https://api.github.com/users/asterite/gists{/gist_id}","starred_url":"https://api.github.com/users/asterite/starred{/owner}{/repo}","subscriptions_url":"https://api.github.com/users/asterite/subscriptions","organizations_url":"https://api.github.com/users/asterite/orgs","repos_url":"https://api.github.com/users/asterite/repos","events_url":"https://api.github.com/users/asterite/events{/privacy}","received_events_url":"https://api.github.com/users/asterite/received_events","type":"User","site_admin":false},"body":"This PR changes the generated code for comparisons of signed vs. unsigned integers to always give the correct result.\r\n\r\nIf both numbers are not known at compile time, it's twice slower than before. For example:\r\n\r\n```crystal\r\nnums1 = Array.new(20_000) { rand(0..255).to_u8 }\r\nnums2 = Array.new(20_000) { rand(-1000..1000).to_i32 }\r\n\r\ntotal = 0\r\n\r\ntime = Time.now\r\nnums1.each do |n1|\r\n  nums2.each do |n2|\r\n    total += 1 if n1 < n2\r\n  end\r\nend\r\nputs Time.now - time\r\n\r\nputs total\r\n``` \r\n\r\nBefore: 0.205s\r\nAfter: 0.394s\r\n\r\nIf one of the numbers is known at compile-time, the performance stays the same as before.\r\n\r\nSince unsigned numbers are not commonly used (in application-level code I imagine Int32 or Int64 used a lot, and unsigned numbers mostly for C interoperability), I'd say to make this change. It's better to avoid incorrect runtime results. And you can always cast one of the numbers to the other type if you are sure it will fit, and get the performance 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