Inspired by Haskells: http://tinyurl.com/3c3yor
ffib=:(+&*:,]*]-~+:@[)/@]`((+&*:,~[*[++:@])/@])@.({...@[)/@(1x 0,~,.@|....@#:)
ffib"0 i.8
1 0
1 1
2 1
3 2
5 3
8 5
13 8
21 13
ts '{: ffib 100001'
0.748854 265536
11{. ": {: ffib 100001
42026927029
(slower) variants:
ffib2=: (+&*:,+:@*-*:@])/@]`((+&*:,~*:@[++:@*)/@])@.({...@[)/@(1x
0,~,.@|....@#:)
ffib3=: (,+/ .*~,,:],-)/@]`(((,~,:~[,+)+/ .*,~)/@])@.({...@[)/@(1x
0,~,.@|....@#:)
=@@i
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