Re: methods used by compilers for switch{ case } statements?

  mathog@seqaxp.bio.caltech.edu wrote:


>>>Can someone please point me to an online reference which describes the
>>>mechanism(s) compilers use to implement the switch/case statement in
>>>C? Specifically, which method or methods does the object code
>>>implement?


      You've asked an under-constrained question. Primarily because
      the mechanisms are highly dependent on the target machine.


      Further, it is also very dependent on things like the
      density of cases (e.g. a reasonably contiguous range of values)


      For example, on a VAX, there was a CASE instruction that took
      an index value, an offset and a table size (N), followed by N
      PC-relative offsets.




      Most reasonable compilers try to calculate some sort of time-space
      tradeoff between using a dispatch table and generating if-then-else.


      Some compilers build hash functions between the index values and
      the jump-addresses. It all depends on how much effort you're
      willing to invest in your compiler....


      ANY tradeoff discussions as to which technique to apply have to
      be made in the context of a target architecture.


-- Al Lehotsky
--
                                Quality Software Management
                          http://www.tiac.net/users/lehotsky

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