[GHC] #5944: Bad hpc hash function

[GHC]

#5944: Bad hpc hash function
------------------------------+---------------------------------------------
 Reporter:  Lennart           |          Owner:  andy@…          
     Type:  bug               |         Status:  new             
 Priority:  normal            |      Component:  Code Coverage   
  Version:  7.2.2             |       Keywords:                  
       Os:  Unknown/Multiple  |   Architecture:  Unknown/Multiple
  Failure:  None/Unknown      |       Testcase:                  
Blockedby:                    |       Blocking:                  
  Related:                    |  
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 In the hpc module Trace.Hpc.Util there is the following code:

 {{{
 instance (HpcHash a,HpcHash b) => HpcHash (a,b) where
   toHash (a,b) = toHash a * 33 `hxor` toHash b
 }}}

 This is bad and I can only presume that what was actually intended was

 {{{
 instance (HpcHash a,HpcHash b) => HpcHash (a,b) where
   toHash (a,b) = (toHash a * 33) `hxor` toHash b
 }}}

 Otherwise a hash of 0 for a will result in a total hash of 0.

-- 
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/5944>
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