RandomSourceBase.NextDoubleNonZero() can produce zero #5
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colgreen
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- Doubled sampling resolution of NextDoubleNonZero(). - Added IRandomSource.NextFloatNonZero(). - Reordered methods in IRandomSource to a slightly more logical order - Removed [MethodImpl(MethodImplOptions.AggressiveInlining)] in a few places, as the JIT compiler will inline where appropriate without this hint. - Added RandomSourceBaseTests; this performs bounds checks on most of the IRandomSource methods.
colgreen
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Fix: NextDoubleNonZero() could return zero (#5)
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Fixed in the 9.x maintenance branch in release 9.1.1. A fix for the master branch is pending. |
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Fixed in master branch, and v11.0.0 release. |
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This:
return ((NextULongInner() >> 11) & 0x1f_ffff_ffff_fffe) * INCR_DOUBLE;Should be:
return (((NextULongInner() >> 11) & 0x1f_ffff_ffff_fffe)+1) * INCR_DOUBLE;Otherwise a zero will be returned when NextULongInner() returns zero, which is approximately every 2^64 calls (approx. 1.8*10^19) if the underlying PRNG is capable of generating zero, which all of the redzen PRNGs are. This makes the error an exceedingly rare event, but it is possible and thus a definite bug. E.g. if this method were called a billion times a second, then we can expect to see a zero approximately once every 31 years!
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