Move ConcurrentQueueSegment<T>.RoundUpToPowerOf2 to BitOperations #50070
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I couldn't figure out the best area label to add to this PR. If you have write-permissions please help me learn by adding exactly one area label. |
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Tagging subscribers to this area: @tannergooding, @pgovind Issue DetailsContributes to #43135
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| internal static uint RoundUpToPowerOf2(uint value) | ||
| { | ||
| // TODO: https://github.com/dotnet/runtime/issues/43135 | ||
| // When this is exposed publicly, decide on behavior be for the boundary cases... |
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For reference, the main two concerns are 0 and overflow (int.MaxValue + 2 through uint.MaxValue).
Given 0 is not a power of two, it makes sense for this to return 1. This is what the lzcnt path returns, but the bithacks implementation returns 0 and needs an additional value += (value == 0) ? 1 : 0.
Likewise, the "logical" solution for overflow cases is to return 0, representing the lowest 32-bits of a theoretically infinitely precise result. This is what the bithacks version returns (unless modified to account for rounding up) but the lzcnt variant ends up shifting by 32 which causes it to return 1 instead.
It would be great if we can figure out trivial additions to get the expected result in both cases without significant overhead.
ghost
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Contributes to #43135
cc: @tannergooding