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From: Andre McCurdy <armccurdy@gmail.com>
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Subject: expectations for a_ctz_64(0)
Date: Thu, 30 Nov 2017 14:41:32 -0800
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Currently the generic and aarch64 versions of a_ctz_64() give
different results for 0:

  a_ctz_64_generic(0) : 0
  a_ctz_64_aarch64(0) : 64

That doesn't matter for the ffs functions, but for the other users of
a_ctz_l and a_ctz_64 (ie malloc and qsort) it's less clear.

Does musl rely on a specific behaviour?