RFR: 8257985: count_trailing_zeros doesn't handle 64-bit values on 32-bit JVM [v2]
Claes Redestad
redestad at openjdk.java.net
Fri Dec 11 11:24:08 UTC 2020
> 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:
Fix Windows 32-bit variant, improve commentary
-------------
Changes:
- all: https://git.openjdk.java.net/jdk/pull/1747/files
- new: https://git.openjdk.java.net/jdk/pull/1747/files/7ecdd76b..1b012194
Webrevs:
- full: https://webrevs.openjdk.java.net/?repo=jdk&pr=1747&range=01
- incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=1747&range=00-01
Stats: 4 lines in 1 file changed: 2 ins; 0 del; 2 mod
Patch: https://git.openjdk.java.net/jdk/pull/1747.diff
Fetch: git fetch https://git.openjdk.java.net/jdk pull/1747/head:pull/1747
PR: https://git.openjdk.java.net/jdk/pull/1747
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