Some all but random responses. First,
<begin extract> That's all well and good for two character values but obviously doesn't scale beyond a half-word. </end extract> The problem I was addressing was a two-character/halfword one, and I raised it originally to illustrate one egregious way in which the IBM Enterprise COBOL compilers were deficient in their handling of language constructs, specifically EVALUATE for one- and two-character arguments. I chose this example because there are canonical, well understood, and not at all controversial branch-table based schemes available for implementing C switch statements and PL/I select(<single character>) groups. I was not proposing a panacea, about any and all of which I am generically suspicious. Next, <begin extract> I'm glad I said "median", rather than "mode". For the latter frequency statistics would be required. </end extract> Frequency statistics are required for the former too. To say otherwise is to confound frequency class-interval definitions with their associated counts. The 'exponential' vs 'logarithmic' issue is more complicated, but here I do concede that these two algorithms are better contrasted using 'polynomial time' and 'logarithmic time'. I come now to <begin extract> If all the keys are already known then a perfect hash optimized switch statement is one of the most efficient methods I've seen. Especially popular with compiler writers for the symbol table. </end extract> It seems to me to mix two topics. The reserved or key words of a statement-level language are "already known". The identifiers used in a source program written in such a language are not. (One could of course conjecture that 'I' or 'i' will be used as the identifier of an indexing subscript in many, even most FORTRAN programs; but I am not sure that this sort of thing would be very helpful.) The C language switch statement is defined very specifically and carefully as an SBCS single-character facility. Not at all incidentally, this definition ensures that branch tables can always be used to implement a C switch statement. I do agree, if that be the right word, that hashing schemes have historically been much used for symbol-table management by the writers of compilers and assemblers. (If challenged before the fact, I should also be quite willing to 'agree' that the earth is an oblate spheroid.) John Gilmore, Ashland, MA 01721 - USA ---------------------------------------------------------------------- For IBM-MAIN subscribe / signoff / archive access instructions, send email to lists...@listserv.ua.edu with the message: INFO IBM-MAIN
