{"action":"created","issue":{"url":"https://api.github.com/repos/JuliaLang/julia/issues/22758","repository_url":"https://api.github.com/repos/JuliaLang/julia","labels_url":"https://api.github.com/repos/JuliaLang/julia/issues/22758/labels{/name}","comments_url":"https://api.github.com/repos/JuliaLang/julia/issues/22758/comments","events_url":"https://api.github.com/repos/JuliaLang/julia/issues/22758/events","html_url":"https://github.com/JuliaLang/julia/issues/22758","id":242148270,"number":22758,"title":"Loss of accuracy of BigFloat on Win10-64bit plattform","user":{"login":"egarten","id":30087458,"avatar_url":"https://avatars0.githubusercontent.com/u/30087458?v=4","gravatar_id":"","url":"https://api.github.com/users/egarten","html_url":"https://github.com/egarten","followers_url":"https://api.github.com/users/egarten/followers","following_url":"https://api.github.com/users/egarten/following{/other_user}","gists_url":"https://api.github.com/users/egarten/gists{/gist_id}","starred_url":"https://api.github.com/users/egarten/starred{/owner}{/repo}","subscriptions_url":"https://api.github.com/users/egarten/subscriptions","organizations_url":"https://api.github.com/users/egarten/orgs","repos_url":"https://api.github.com/users/egarten/repos","events_url":"https://api.github.com/users/egarten/events{/privacy}","received_events_url":"https://api.github.com/users/egarten/received_events","type":"User","site_admin":false},"labels":[{"id":611168704,"url":"https://api.github.com/repos/JuliaLang/julia/labels/bignums","name":"bignums","color":"f1791e","default":false},{"id":2385601,"url":"https://api.github.com/repos/JuliaLang/julia/labels/upstream","name":"upstream","color":"bbbbbb","default":false},{"id":5669611,"url":"https://api.github.com/repos/JuliaLang/julia/labels/windows","name":"windows","color":"0b02e1","default":false}],"state":"open","locked":false,"assignee":null,"assignees":[],"milestone":null,"comments":10,"created_at":"2017-07-11T18:52:03Z","updated_at":"2017-07-18T13:11:52Z","closed_at":null,"body":"I found an issue regarding BigFloats using julia0.6.0 on a Win10 system. This error does not appear on linux or macOS systems:\r\n```\r\n# Set precision to 7 million bits, so I expect about 2 million valid digits\r\nsetprecision(7000000)\r\n# Get value of pi with high precision\r\nbigpi=BigFloat(pi)\r\n# Calculate difference of sin(pi/2)-1. Should be zero in exact arithmetic\r\nsin(bigpi/BigFloat(2))-1\r\n# Calualate difference of sin(pi/6)-1/2. Should be zero in exact arithmetic\r\nsin(bigpi/BigFloat(6))-1/BigFloat(2)\r\n```\r\n\r\nFor the first difference I get the value of zero. That means the result of sin(pi/2) is valid up to 2 million digits.\r\n\r\nFor the seconds difference I get an value of about 4.76993...e-306923. That means sin(pi/6) is only calculated up to about 300,000 digits and not 2 million digits.\r\n\r\nSome more details have already been discussed:\r\nhttps://discourse.julialang.org/t/accuracy-of-bigfloat-calculating-sin-with-high-accuracy/4604\r\n\r\n"},"comment":{"url":"https://api.github.com/repos/JuliaLang/julia/issues/comments/316058996","html_url":"https://github.com/JuliaLang/julia/issues/22758#issuecomment-316058996","issue_url":"https://api.github.com/repos/JuliaLang/julia/issues/22758","id":316058996,"user":{"login":"stevengj","id":2913679,"avatar_url":"https://avatars3.githubusercontent.com/u/2913679?v=4","gravatar_id":"","url":"https://api.github.com/users/stevengj","html_url":"https://github.com/stevengj","followers_url":"https://api.github.com/users/stevengj/followers","following_url":"https://api.github.com/users/stevengj/following{/other_user}","gists_url":"https://api.github.com/users/stevengj/gists{/gist_id}","starred_url":"https://api.github.com/users/stevengj/starred{/owner}{/repo}","subscriptions_url":"https://api.github.com/users/stevengj/subscriptions","organizations_url":"https://api.github.com/users/stevengj/orgs","repos_url":"https://api.github.com/users/stevengj/repos","events_url":"https://api.github.com/users/stevengj/events{/privacy}","received_events_url":"https://api.github.com/users/stevengj/received_events","type":"User","site_admin":false},"created_at":"2017-07-18T13:11:52Z","updated_at":"2017-07-18T13:11:52Z","body":"Great, looks like they have a fix for MPFR 3.1.   We could apply a patch before then if need be."}}
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