JDK-8179004 : Add an efficient implementation of the "count trailing zeros" operation
  • Type: Enhancement
  • Component: hotspot
  • Sub-Component: runtime
  • Affected Version: 9
  • Priority: P4
  • Status: Resolved
  • Resolution: Fixed
  • OS: generic
  • CPU: generic
  • Submitted: 2017-04-20
  • Updated: 2017-08-25
  • Resolved: 2017-05-06
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JDK 10
10 b21Fixed
Related Reports
Relates :  
JDK-6735527 - Bitmap - speed up searches
Description
There are a number of possible uses for an efficient "count trailing zero" operation.  By efficient we mean access to the underlying hardware support; supported hardware architectures generally provide an efficient implementation, e.g. a single instruction or a short instruction sequence.

One obvious use is in the BitMap search functions, which are presently performing that operation using a for-loop to iterate over the bits in the word of interest.  See JDK-6735527.