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Ticket #7226 (closed Bugs: fixed)

Opened 20 months ago

Last modified 19 months ago

relax() in relax.hpp can return false even if predecessor map is changed

Reported by: Alex Hagen-Zanker <ahh34@…> Owned by: jewillco
Milestone: To Be Determined Component: graph
Version: Boost 1.51.0 Severity: Problem
Keywords: relax, floating point precision Cc:

Description

The relax function in relax.hpp checks whether the distance of an edge really is reduced after relaxation and only returns true if that is the case. (the alternative possibility is that the expected reduction in distance does not take place due to floating point precision).

However, the function updates the predecessor map in any case. It is therefore possible that the predecessor map is changed while the relax function returns false. I suppose this is a bug, even though I did not cause me any trouble.

Attachments

relax.patch Download (1.2 KB) - added by Alex Hagen-Zanker <ahh34@…> 20 months ago.
patch

Change History

Changed 20 months ago by Alex Hagen-Zanker <ahh34@…>

patch

comment:1 Changed 19 months ago by jewillco

  • Status changed from new to closed
  • Resolution set to fixed

(In [80639]) Fixed relax logic to not write predecessor map unless distance was actually changed in memory (although this case will never be hit unless registers have extra precision compared to memory); fixes #7226

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