[GHC] #14882: memchr#

[GHC]

#14882: memchr#
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        Reporter:  andrewthad        |                Owner:  (none)
            Type:  feature request   |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Compiler          |              Version:  8.2.2
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):  Phab:D4472
       Wiki Page:                    |
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Comment (by andrewthad):

 It's good to hear what the actual motivation was for bringing `memcpy` in.
 I cannot provide a similarly compelling performance-oriented reason for
 `memchr`. I think that in
 https://ghc.haskell.org/trac/ghc/ticket/14882#comment:8, hvr makes the
 best argument I could offer: that all of the other C99 memory primitives
 are already wrapped by `ghc-prim` and this one would complete the set.

 I disagree that `memchr` is difficult to implement a wrapper for in the
 compiler. In the differential I linked, the actual implementation is about
 20 lines code. Some of the others are certainly more complicated though.
 The fact `memcpy` takes two arrays means the GHC needs several variants of
 it dealing with various combinations of `ByteArray#`, `MutableByteArray#`,
 and `Addr#`, (GHC has 5 variants of `copyByteArray#`) but `memchr` only
 takes a single array, so even the most complete wrapping of it possible
 would only need three implementations. I've only done one so far since it
 was the only one I needed.

 > Where does it stop?

 I think that it would stop where the C99 memory primitives stop. So,
 nothing like `memset_s`, `rawmemchr`, etc.

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14882#comment:14>
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