0.9b (c) 1995 Peter Childs

SHELL-Sortroutine fromSteve Pitts(see EMail Addresses) Captured from a message in a public CompuServe Forum

/* Routine SHELLSORT. */ /* */ /* This REXX subroutine can be used to perform a generic sort. It has */ /* been written in a generic fashion to make it as easy as possible */ /* to plug it into the EXEC of your choice. The algorithm used is the */ /* fastest non-recursive one that I know of for lists in random */ /* sequence, but if you've got one that's faster, then I challenge */ /* you to produce an equivalent of this routine using your algorithm. */ /* */ /* Before calling this procedure you need to have set up two arrays, */ /* key. and ind., containing, respectively, the key field for */ /* comparison purposes, and an index (or pointer) to each element. */ /* */ /* The subroutine takes two numeric arguments representing the first */ /* and last elements to be sorted, and returns ind. as a pointer list */ /* in ascending order. To change it to sort into descending order all */ /* you need do is change the line that compares key.kind to tempdat */ /* so that the test is inverted (ie. > becomes <). Alternatively you */ /* could process the index in reverse order (see below). */ /* */ /* Thus if you had done a CP QUERY RDR ALL into a variable RDRLIST. */ /* you would code the following to sort it into file name order: */ /* */ /* do i=1 to rdrlist.0 */ /* key.i=substr(rdrlist.i,54,8) */ /* ind.i=i */ /* end */ /* */ /* call shellsort 2,rdrlist.0 */ /* */ /* Note that the first index is 2 because rdrlist.1 is a header line. */ /* */ /* To print the list in sorted order you would then code: */ /* */ /* do i=1 to rdrlist.0 */ /* rind=ind.i */ /* say rdrlist.rind */ /* end */ /* */ /* Note the use of the pointer. Unfortunately it is not possible to */ /* code rdrlist.(ind.i) to get the same effect in a single statement. */ /* To display items in descending order you simply reverse the loop, */ /* do i=rdrlist.0 to 1 by -1, although this would display the header */ /* at the end, in this instance! */ /* */ /**********************************************************************/ /* */ /* VER TIME DATE BY NARRATIVE */ /* 1.0 15:22 90/02/20 SJP - Original version. Generic sort routine */ /* using Shell algorithm. */ /* 1.1 10:13 90/12/07 SJP - Added check for first element number */ /* not being less than last element */ /* number. */ /* 1.2 09:49 92/02/19 SJP - Moved procedure statement for VM/ESA. */ /* 1.3 10:51 93/08/27 SJP - Tidied up and corrected documentation. */ /* */ /**********************************************************************/ shellsort: PROCEDURE expose key. ind. trace o /* Check that there are at least two elements to sort */ parse arg low, high if low >= high then return /* Calculate an optimal initial gap size */ gap = 1 do while gap < (high-low)+1 gap = gap*3 end /* Basically we sort the elements 'gap' elements */ /* apart, gradually reducing 'gap' until it is one, */ /* at which point the list will be fully sorted. */ do until gap = 1 gap=gap/3 do i=(gap+low) to high j=i tempind=ind.j tempdat=key.tempind k=j-gap kind=ind.k do while key.kind > tempdat ind.j=ind.k j=k k=j-gap if k < low then leave kind=ind.k end ind.j=tempind end end RETURN

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