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Differential D45483

x86: simplify ceil(log2(x)) function
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Authored by dougm on Tue, Jun 4, 5:10 PM.

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rG9ff1462976fc: x86: simplify ceil(log2(x)) function

Summary

A function called mask_width in one place and log2 in the other calculates its value in a more complex way than necessary. A simpler implementation offered here saves a few bytes in the functions that call it. 128 bytes in add_deterministic_cache, in particular.

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rG FreeBSD src repository

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dougm created this revision.Tue, Jun 4, 5:10 PM

Herald added a reviewer: bhyve. · View Herald TranscriptTue, Jun 4, 5:10 PM

Herald added subscribers: bcran, rgrimes. · View Herald Transcript

dougm requested review of this revision.Tue, Jun 4, 5:10 PM

Looks good to me.
A bit ashamed that I could not figure that fls(x - 1) does the job if zero is handled as a special case.

This revision is now accepted and ready to land.Tue, Jun 4, 5:30 PM

alc accepted this revision.Tue, Jun 4, 5:52 PM

alc added inline comments.

sys/amd64/vmm/x86.c
63–64	Update the comment?

Closed by commit rG9ff1462976fc: x86: simplify ceil(log2(x)) function (authored by dougm). · Explain WhyTue, Jun 4, 6:03 PM

This revision was automatically updated to reflect the committed changes.

dougm added a commit: rG9ff1462976fc: x86: simplify ceil(log2(x)) function.

Herald added a subscriber: imp. · View Herald TranscriptTue, Jun 4, 6:03 PM

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sys/

amd64/

vmm/

5 lines

x86/

x86/

6 lines

Diff 139450

sys/amd64/vmm/x86.c

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sys/x86/x86/mp_x86.c

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