math/big: much simplified and faster Float rounding
math/big: much simplified and faster Float rounding

Change-Id: Iab0add7aee51a8c72a81f51d980d22d2fd612f5c
Reviewed-on: https://go-review.googlesource.com/20817
Reviewed-by: Alan Donovan <7069e9552f9d110b0a0f326b96f22f63fb99dfc1@google.com>

ImJasonH/go,linux-on-ibm-z/go,4ad/go,goodlang/good,suncycheng/go,cloudflare/go,golang/go,ImJasonH/go,derekmarcotte/go,golang/go,golang/go,vsekhar/elastic-go,linux-on-ibm-z/go,josharian/go,miolini/go,ImJasonH/go,cloudflare/go,Cofyc/go,Cofyc/go,Cofyc/go,Cofyc/go,goodlang/good,ganboing/go-esx,polyverse-security/go,vanloswang/go,4ad/go,vanloswang/go,akutz/go,ganboing/go-esx,vsekhar/elastic-go,nawawi/go,suncycheng/go,miolini/go,ganboing/go-esx,4ad/go,theif519/go,momchil-velikov/go,theif519/go,cloudflare/go,Cofyc/go,CAFxX/go,codestation/go,nawawi/go,linux-on-ibm-z/go,nawawi/go,ImJasonH/go,ganboing/go-esx,codestation/go,codestation/go,goodlang/good,miolini/go,4ad/go,derekmarcotte/go,suncycheng/go,miolini/go,momchil-velikov/go,suncycheng/go,Cofyc/go,goodlang/good,vsekhar/elastic-go,derekmarcotte/go,momchil-velikov/go,ImJasonH/go,cloudflare/go,vsekhar/elastic-go,polyverse-security/go,akutz/go,miolini/go,codestation/go,linux-on-ibm-z/go,codestation/go,linux-on-ibm-z/go,polyverse-security/go,momchil-velikov/go,miolini/go,Cofyc/go,golang/go,derekmarcotte/go,vanloswang/go,goodlang/good,cloudflare/go,josharian/go,suncycheng/go,nawawi/go,polyverse-security/go,linux-on-ibm-z/go,4ad/go,theif519/go,derekmarcotte/go,miolini/go,ganboing/go-esx,derekmarcotte/go,josharian/go,codestation/go,ImJasonH/go,nawawi/go,vsekhar/elastic-go,suncycheng/go,ImJasonH/go,theif519/go,akutz/go,vsekhar/elastic-go,theif519/go,derekmarcotte/go,akutz/go,suncycheng/go,CAFxX/go,goodlang/good,josharian/go,vanloswang/go,ganboing/go-esx,polyverse-security/go,momchil-velikov/go,CAFxX/go,vanloswang/go,polyverse-security/go,akutz/go,codestation/go,josharian/go,suncycheng/go,josharian/go,cloudflare/go,CAFxX/go,4ad/go,Cofyc/go,linux-on-ibm-z/go,akutz/go,akutz/go,cloudflare/go,nawawi/go,josharian/go,momchil-velikov/go,miolini/go,momchil-velikov/go,derekmarcotte/go,CAFxX/go,golang/go,cloudflare/go,vanloswang/go,akutz/go,vsekhar/elastic-go,christopher-henderson/Go,golang/go,theif519/go,ImJasonH/go,nawawi/go,codestation/go,vsekhar/elastic-go,goodlang/good,polyverse-security/go,CAFxX/go,4ad/go,polyverse-security/go,nawawi/go,goodlang/good,CAFxX/go,momchil-velikov/go,CAFxX/go,theif519/go,4ad/go,linux-on-ibm-z/go,vanloswang/go,theif519/go,golang/go,vanloswang/go,josharian/go,ganboing/go-esx,ganboing/go-esx,golang/go