math/big: Int64() conversion incorrect despite Exact accuracy

[johnSchnake]

Please answer these questions before submitting your issue. Thanks!

What version of Go are you using (go version)?

go version go1.7.1 darwin/amd64

What operating system and processor architecture are you using (go env)?

GOARCH="amd64"
GOBIN=""
GOEXE=""
GOHOSTARCH="amd64"
GOHOSTOS="darwin"
GOOS="darwin"
GOPATH="/Users/johnschnake/go"
GORACE=""
GOROOT="/usr/local/go"
GOTOOLDIR="/usr/local/go/pkg/tool/darwin_amd64"
CC="clang"
GOGCCFLAGS="-fPIC -m64 -pthread -fno-caret-diagnostics -Qunused-arguments -fmessage-length=0 -fdebug-prefix-map=/var/folders/sw/m66hd5gs4jq4rgzr1s_hvv2c0000gn/T/go-build059909108=/tmp/go-build -gno-record-gcc-switches -fno-common"
CXX="clang++"
CGO_ENABLED="1"

What did you do?

If possible, provide a recipe for reproducing the error.
A complete runnable program is good.
A link on play.golang.org is best.
https://play.golang.org/p/iVPRHj3eZ9

What did you expect to see?

"Correct and exact" as output; implying that since math/big accuracy of Float.Int64() reported Exact, that I would get the same value as the same input cast to an int64.

What did you see instead?

"Not equal, despite exact" as output; implying that even though the same values went in as inputs, and math/big reported the conversion could occur w/o rounding, the values were not equal.

[johnSchnake]

Disregard, I see now a few issues with my example. I should have used math.MinInt64 in this particular example and that the loss of precision was occurring when originally cast into the float64 prior to the big.Float.