JDK-8140384: TicksToTimeHelper::milliseconds() should return a double

[David Holmes]

On 23/10/2015 6:41 PM, Markus Gronlund wrote:
> Hi Bengt,
>
> Looks good - thanks for fixing.

Arguably if you asked for milliseconds you really didn't care about the 
fractional part. If you did care then you could just multiply seconds by 
1000. But on that basis we could just drop the milliseconds altogether.

> One small thing:
>
> I think we can drop the return (double) cast on line 55, no need for updated webrevs.

We can drop a most of the double casts This:

static double time_conversion(const Tickspan& span,
                               TicksToTimeHelper::Unit unit) {
    double frequency_per_unit = (double)os::elapsed_frequency() / 
(double)unit;

    return (double) ((double)span.value() / frequency_per_unit);
}

can become just:

  static double time_conversion(const Tickspan& span,
                                TicksToTimeHelper::Unit unit) {
    double frequency_per_unit = os::elapsed_frequency() / (double)unit;

    return span.value() / frequency_per_unit;
}

promotion rules will ensure each expression is of type double.

Cheers,
David

> Thanks
> Markus
>
> -----Original Message-----
> From: Bengt Rutisson
> Sent: den 23 oktober 2015 10:27
> To: serviceability-dev at openjdk.java.net serviceability-dev at openjdk.java.net
> Subject: JDK-8140384: TicksToTimeHelper::milliseconds() should return a double
>
>
> Hi all,
>
> Could I have  a couple of reviews for this small change?
>
> http://cr.openjdk.java.net/~brutisso/8140384/webrev.00/
> https://bugs.openjdk.java.net/browse/JDK-8140384
>
> The TicksToTimeHelper class use different return values depending on if you want to convert to seconds or milliseconds.
>
> class TicksToTimeHelper : public AllStatic {
>    public:
>     enum Unit {
>       SECONDS = 1,
>       MILLISECONDS = 1000
>     };
>     static double seconds(const Tickspan& span);
>     static jlong milliseconds(const Tickspan& span); };
>
> No one is using the conversion to milliseconds() but because it returns a jlong it loses precision.
>
> Making milliseconds() return a double allows for coming uses to get millisecond values with higher precision.
>
> Thanks,
> Bengt
>