RFR: 8257985: count_trailing_zeros doesn't handle 64-bit values on 32-bit JVM [v9]
Kim Barrett
kbarrett at openjdk.java.net
Mon Dec 14 09:11:59 UTC 2020
On Fri, 11 Dec 2020 15:31:09 GMT, Claes Redestad <redestad at openjdk.org> wrote:
>> Re-implement count_trailing_zeros as a template function similar to count_leading_zeros, adding support for 8 and 16 bit types as well as for 64-bit types on 32-bit builds, which is currently not supported. This prohibits implementing the log2i_exact proposed by #1663 using count_trailing_zeros, as suggested during review.
>>
>> Compared to count_leading_zeros the implementation can be slightly simpler since subword specializations can simply use the internal 32-bit variant.
>>
>> Windows doesn't define _BitScanForward64 on 32-bit targets, so the 32-bit variant for handling 64-bit values becomes more convoluted.
>
> Claes Redestad has updated the pull request incrementally with one additional commit since the last revision:
>
> Explicit, static_cast to 32-bit unsigned
Marked as reviewed by kbarrett (Reviewer).
-------------
PR: https://git.openjdk.java.net/jdk/pull/1747
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