Fix to avoid a compile error due to float to int truncation with GCCGO

[inatatsu]

The unit test pkg/units/size_test.go fails with GCCGO due to a compilation error:

inagaki@black3:~/upstream/src/github.com/docker/docker/pkg/units$ go version
go version gccgo (GCC) 5.0.0 20141029 (experimental) linux/amd64
inagaki@black3:~/upstream/src/github.com/docker/docker/pkg/units$ go test
# _/home/inagaki/upstream/src/github.com/docker/docker/pkg/units
./size_test.go:28:43: error: floating point constant truncated to integer
  assertEquals(t, "2.22 PB", HumanSize(2.22*PB))
                                           ^
FAIL    _/home/inagaki/upstream/src/github.com/docker/docker/pkg/units [build failed]
inagaki@black3:~/upstream/src/github.com/docker/docker/pkg/units$

According to the discussion on GCC Bugzilla, this is due to the difference between GCCGO and GC in the implementations of floating point constant expression. The language specifies that a compiler raises an error when a floating point constant expression is truncated to integer, a precision of the internal representation is implementation-dependent. While my workaround is modifying size_test.go as:

assertEquals(t, "2.22 PB", HumanSize(int64(float64(2.22*PB))))

, is it better to modify the parameter of HumanSize() from int64 to float64 like BytesSize()?
Signed-off-by: Tatsushi Inagaki e29253@jp.ibm.com

[crosbymichael]

I would probably change HumanSize to take a float64

[inatatsu]

Modified HumanSize() to take a float64 parameter and added casts to float64 around the arguments for HumanSize() .

[inatatsu]

@vieux @jfrazelle Do we need additional changes to merge this PR? This problem can occur even with GC depending on the value of floating point constant.

[vbatts]

LGTM

[inatatsu]

@crosbymichael ping?

[crosbymichael]

LGTM

[tiborvass]

@crosbymichael Unit tests are failing, why did we merge this?

[unclejack]

This wasn't needed any more. A much smaller PR was #9715 and it fixed the same problem. This PR introduced a conflict with master once that was merged.

I'm going to send a revert PR for this one.

[tiborvass]

FYI, instead of reverting this PR, we fixed the compile errors in the unit tests.