universal compaction picker: use double for potential overflow
universal compaction picker: use double for potential overflow

Summary: There is a possible overflow case in universal compaction picker. Use double to make the logic straight-forward

Test Plan: make all check

Reviewers: yhchiang, igor, MarkCallaghan, ljin

Reviewed By: ljin

Subscribers: leveldb

Differential Revision: https://reviews.facebook.net/D23817

facebook/rocksdb,NickCis/rocksdb,temicai/rocksdb,vmx/rocksdb,tizzybec/rocksdb,fengshao0907/rocksdb,geraldoandradee/rocksdb,Vaisman/rocksdb,amyvmiwei/rocksdb,Vaisman/rocksdb,IMCG/RcoksDB,JackLian/rocksdb,temicai/rocksdb,IMCG/RcoksDB,Andymic/rocksdb,ylong/rocksdb,zhangpng/rocksdb,makelivedotnet/rocksdb,alihalabyah/rocksdb,vashstorm/rocksdb,anagav/rocksdb,skunkwerks/rocksdb,siddhartharay007/rocksdb,ryneli/rocksdb,luckywhu/rocksdb,fengshao0907/rocksdb,flabby/rocksdb,ryneli/rocksdb,siddhartharay007/rocksdb,tsheasha/rocksdb,siddhartharay007/rocksdb,Applied-Duality/rocksdb,mbarbon/rocksdb,SunguckLee/RocksDB,SunguckLee/RocksDB,vashstorm/rocksdb,virtdb/rocksdb,IMCG/RcoksDB,anagav/rocksdb,amyvmiwei/rocksdb,geraldoandradee/rocksdb,makelivedotnet/rocksdb,vashstorm/rocksdb,mbarbon/rocksdb,virtdb/rocksdb,JohnPJenkins/rocksdb,anagav/rocksdb,fengshao0907/rocksdb,IMCG/RcoksDB,biddyweb/rocksdb,wat-ze-hex/rocksdb,ylong/rocksdb,alihalabyah/rocksdb,kaschaeffer/rocksdb,facebook/rocksdb,mbarbon/rocksdb,NickCis/rocksdb,biddyweb/rocksdb,hobinyoon/rocksdb,virtdb/rocksdb,bbiao/rocksdb,SunguckLee/RocksDB,wenduo/rocksdb,geraldoandradee/rocksdb,jalexanderqed/rocksdb,siddhartharay007/rocksdb,RyanTech/rocksdb,SunguckLee/RocksDB,amyvmiwei/rocksdb,vashstorm/rocksdb,OverlordQ/rocksdb,flabby/rocksdb,mbarbon/rocksdb,Andymic/rocksdb,SunguckLee/RocksDB,facebook/rocksdb,rDSN-Projects/rocksdb.replicated,wenduo/rocksdb,Applied-Duality/rocksdb,JoeWoo/rocksdb,OverlordQ/rocksdb,mbarbon/rocksdb,bbiao/rocksdb,wlqGit/rocksdb,flabby/rocksdb,biddyweb/rocksdb,vmx/rocksdb,tsheasha/rocksdb,wat-ze-hex/rocksdb,norton/rocksdb,JackLian/rocksdb,bbiao/rocksdb,norton/rocksdb,wenduo/rocksdb,norton/rocksdb,NickCis/rocksdb,NickCis/rocksdb,rDSN-Projects/rocksdb.replicated,makelivedotnet/rocksdb,JoeWoo/rocksdb,wat-ze-hex/rocksdb,fengshao0907/rocksdb,sorphi/rocksdb,caijieming-baidu/rocksdb,NickCis/rocksdb,alihalabyah/rocksdb,amyvmiwei/rocksdb,tsheasha/rocksdb,Andymic/rocksdb,IMCG/RcoksDB,sorphi/rocksdb,zhangpng/rocksdb,RyanTech/rocksdb,wat-ze-hex/rocksdb,facebook/rocksdb,skunkwerks/rocksdb,norton/rocksdb,caijieming-baidu/rocksdb,JackLian/rocksdb,vmx/rocksdb,lgscofield/rocksdb,caijieming-baidu/rocksdb,siddhartharay007/rocksdb,kaschaeffer/rocksdb,Andymic/rocksdb,OverlordQ/rocksdb,jalexanderqed/rocksdb,caijieming-baidu/rocksdb,tsheasha/rocksdb,sorphi/rocksdb,skunkwerks/rocksdb,wskplho/rocksdb,rDSN-Projects/rocksdb.replicated,luckywhu/rocksdb,JohnPJenkins/rocksdb,dkorolev/rocksdb,temicai/rocksdb,wat-ze-hex/rocksdb,Vaisman/rocksdb,Andymic/rocksdb,tizzybec/rocksdb,temicai/rocksdb,skunkwerks/rocksdb,skunkwerks/rocksdb,ylong/rocksdb,JoeWoo/rocksdb,zhangpng/rocksdb,vmx/rocksdb,makelivedotnet/rocksdb,JackLian/rocksdb,Applied-Duality/rocksdb,norton/rocksdb,JohnPJenkins/rocksdb,wat-ze-hex/rocksdb,flabby/rocksdb,facebook/rocksdb,vmx/rocksdb,RyanTech/rocksdb,lgscofield/rocksdb,norton/rocksdb,JackLian/rocksdb,mbarbon/rocksdb,JoeWoo/rocksdb,flabby/rocksdb,RyanTech/rocksdb,lgscofield/rocksdb,anagav/rocksdb,zhangpng/rocksdb,wskplho/rocksdb,wat-ze-hex/rocksdb,JohnPJenkins/rocksdb,Applied-Duality/rocksdb,JoeWoo/rocksdb,kaschaeffer/rocksdb,RyanTech/rocksdb,facebook/rocksdb,Andymic/rocksdb,geraldoandradee/rocksdb,NickCis/rocksdb,tizzybec/rocksdb,amyvmiwei/rocksdb,dkorolev/rocksdb,Applied-Duality/rocksdb,wskplho/rocksdb,alihalabyah/rocksdb,wskplho/rocksdb,jalexanderqed/rocksdb,lgscofield/rocksdb,bbiao/rocksdb,wlqGit/rocksdb,tizzybec/rocksdb,JoeWoo/rocksdb,norton/rocksdb,bbiao/rocksdb,JohnPJenkins/rocksdb,alihalabyah/rocksdb,kaschaeffer/rocksdb,rDSN-Projects/rocksdb.replicated,lgscofield/rocksdb,kaschaeffer/rocksdb,wenduo/rocksdb,rDSN-Projects/rocksdb.replicated,caijieming-baidu/rocksdb,rDSN-Projects/rocksdb.replicated,OverlordQ/rocksdb,wenduo/rocksdb,luckywhu/rocksdb,SunguckLee/RocksDB,virtdb/rocksdb,virtdb/rocksdb,rDSN-Projects/rocksdb.replicated,hobinyoon/rocksdb,jalexanderqed/rocksdb,caijieming-baidu/rocksdb,bbiao/rocksdb,Andymic/rocksdb,kaschaeffer/rocksdb,dkorolev/rocksdb,tsheasha/rocksdb,bbiao/rocksdb,biddyweb/rocksdb,hobinyoon/rocksdb,sorphi/rocksdb,flabby/rocksdb,biddyweb/rocksdb,ryneli/rocksdb,zhangpng/rocksdb,ryneli/rocksdb,SunguckLee/RocksDB,fengshao0907/rocksdb,anagav/rocksdb,tsheasha/rocksdb,siddhartharay007/rocksdb,hobinyoon/rocksdb,tizzybec/rocksdb,IMCG/RcoksDB,virtdb/rocksdb,flabby/rocksdb,vashstorm/rocksdb,dkorolev/rocksdb,sorphi/rocksdb,biddyweb/rocksdb,mbarbon/rocksdb,Applied-Duality/rocksdb,amyvmiwei/rocksdb,ylong/rocksdb,caijieming-baidu/rocksdb,luckywhu/rocksdb,JackLian/rocksdb,vashstorm/rocksdb,dkorolev/rocksdb,hobinyoon/rocksdb,luckywhu/rocksdb,biddyweb/rocksdb,zhangpng/rocksdb,geraldoandradee/rocksdb,SunguckLee/RocksDB,jalexanderqed/rocksdb,amyvmiwei/rocksdb,temicai/rocksdb,anagav/rocksdb,virtdb/rocksdb,skunkwerks/rocksdb,vmx/rocksdb,dkorolev/rocksdb,luckywhu/rocksdb,luckywhu/rocksdb,temicai/rocksdb,bbiao/rocksdb,ylong/rocksdb,makelivedotnet/rocksdb,JohnPJenkins/rocksdb,Andymic/rocksdb,geraldoandradee/rocksdb,temicai/rocksdb,anagav/rocksdb,Vaisman/rocksdb,makelivedotnet/rocksdb,skunkwerks/rocksdb,wlqGit/rocksdb,facebook/rocksdb,hobinyoon/rocksdb,facebook/rocksdb,ylong/rocksdb,JackLian/rocksdb,wat-ze-hex/rocksdb,sorphi/rocksdb,norton/rocksdb,tsheasha/rocksdb,JohnPJenkins/rocksdb,vmx/rocksdb,tsheasha/rocksdb,Vaisman/rocksdb,wenduo/rocksdb,lgscofield/rocksdb,wskplho/rocksdb,Vaisman/rocksdb,siddhartharay007/rocksdb,fengshao0907/rocksdb,wlqGit/rocksdb,JoeWoo/rocksdb,wlqGit/rocksdb,tizzybec/rocksdb,jalexanderqed/rocksdb,alihalabyah/rocksdb,makelivedotnet/rocksdb,wenduo/rocksdb,ryneli/rocksdb,OverlordQ/rocksdb,RyanTech/rocksdb,wlqGit/rocksdb,sorphi/rocksdb,lgscofield/rocksdb,hobinyoon/rocksdb,OverlordQ/rocksdb,wskplho/rocksdb,wenduo/rocksdb,OverlordQ/rocksdb,ylong/rocksdb,ryneli/rocksdb,jalexanderqed/rocksdb,hobinyoon/rocksdb,Applied-Duality/rocksdb,kaschaeffer/rocksdb,IMCG/RcoksDB,wlqGit/rocksdb,vmx/rocksdb,zhangpng/rocksdb,ryneli/rocksdb,NickCis/rocksdb,wskplho/rocksdb,geraldoandradee/rocksdb,dkorolev/rocksdb,vashstorm/rocksdb,tizzybec/rocksdb,fengshao0907/rocksdb,alihalabyah/rocksdb,Vaisman/rocksdb,RyanTech/rocksdb