[GHC] #1687: A faster (^)-function.

[GHC]

#1687: A faster (^)-function.
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        Reporter:  moonlite@…    |            Owner:
            Type:  bug           |           Status:  new
        Priority:  normal        |        Milestone:  _|_
       Component:  Prelude       |          Version:  6.6.1
      Resolution:                |         Keywords:
Operating System:  Linux         |     Architecture:  x86
 Type of failure:  None/Unknown  |       Difficulty:  Unknown
       Test Case:                |       Blocked By:
        Blocking:                |  Related Tickets:
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Changes (by rwbarton):

 * cc: rwbarton@… (added)


Comment:

 moonlite's algorithm does squaring and multiplication by the small number
 `x`, while GHC's algorithm does squaring and multiplication of those
 squares together in an accumulator.  Squaring big integers is a constant
 factor faster than multiplying different numbers of similar size, so
 moonlite's algorithm wins on Integer when the numbers involved are large.

 The downside is that it is not tail-recursive, which costs when
 multiplications are actually very cheap like for Int.

 But anyways, how about binding to `mpz_pow_ui` and using a RULE in the
 case of Integer base?

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/1687#comment:13>
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