• d-bugmail puremagic.com (23/23) Jul 10 2018 https://issues.dlang.org/show_bug.cgi?id=19075

d-bugmail puremagic.com writes:

https://issues.dlang.org/show_bug.cgi?id=19075

          Issue ID: 19075
           Summary: rt.util.random.Rand48.defaultSeed should prefer RDTSC
                    or mach_absolute_time to ctime.time
           Product: D
           Version: D2
          Hardware: x86_64
                OS: All
            Status: NEW
          Severity: enhancement
          Priority: P1
         Component: druntime
          Assignee: nobody puremagic.com
          Reporter: n8sh.secondary hotmail.com

`rt.util.random.Rand48.defaultSeed` generates a seed from the clock using
`ctime.time`. With `D_InlineAsm_X86_64` it would be better to use the `rdtsc`
instruction because it is much faster as well as being finer precision. (Finer
precision is a benefit not because we care about accurate time, but because the
differences between seeds generated this way are potentially greater.) The same
is true of `mach_absolute_time` on macOS. The Microsoft Windows equivalent
would be `QueryPerformanceCounter` but I haven't benchmarked it to verify that
it is faster than `ctime.time`.

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