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/* genmergesort.h - generate code to do a mergesort */ |
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|
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/* Copyright 1991 Mark Russell, University of Kent at Canterbury. |
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* |
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* You can do what you like with this source code as long as |
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* you don't try to make money out of it and you include an |
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* unaltered copy of this message (including the copyright). |
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*/ |
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|
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/* @(#)genmergesort.h 1.6 26/4/92 (UKC) */ |
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|
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/* GENERIC_MERGE_SORT generates the code necessary to mergesort |
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* an arbitrary linked list. The arguments are: |
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* |
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* storageclass: |
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* should be static or extern. Detrmines the storage class |
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* of the function generated. |
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* |
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* name: the name of the function to be generated |
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* |
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* type: |
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* the type of the elements of the list |
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* for a structure xxst, the type will be: struct xxst |
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* |
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* next: |
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* the name of the field linking the list |
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* |
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* As an example, consider a structure struct xxst, with a link field |
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* "struct xxst *xx_next". Then the following macro: |
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* |
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* GENERIC_MERGE_SORT(static, sortxx, struct xxst, xx_next) |
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* |
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* would generate a static function sortxx: |
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* |
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* static struct xxst *sortxx(list, len, cmp) |
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* struct xxst *list; |
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* int len, (*cmp)(); |
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* |
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* where list is the head of the list to be sorted, len is the length |
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* of this list, and cmp is a comparison function, called in the style |
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* |
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* (*cmp)(xx1, xx2) |
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* |
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* This should return -1, 0 or 1 according as the first argument should |
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* be considered less than, equal to, or greater than the second. |
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* |
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* sortxx() returns a pointer to the head of the sorted list. |
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* |
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* The macro also generates the static functions split_name() and |
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* merge_name, where "name" is what you supplied to the macro. |
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* These functions are for the use of the sort routine only. |
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*/ |
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|
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#define GENERIC_MERGE_SORT(storageclass,name,type,next) \ |
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\ |
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/* Mergesort a linked list of structures of type type. |
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* List is a pointer to the head of the list, len is the number of |
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* elements in the list, and cmp is the comparison function |
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* as described above. Return a pointer to the head of the sorted list. |
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* |
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* Uses the standard recursive mergesort algorithm (see e.g. Kruse) |
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*/ \ |
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\ |
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static type *CAT(name,_split)(type *list, int len);\ |
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\ |
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/* split list, which has len elements at element len/2. Return |
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* a pointer to the second half of the list. |
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*/ \ |
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static type *CAT(name,_split)(type *list,int len) \ |
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{ \ |
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type *prev; \ |
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\ |
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prev = NULL; /* to satisfy gcc */ \ |
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for (; len > 0; --len) { \ |
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prev = list; \ |
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list = list->next; \ |
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} \ |
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prev->next = NULL; \ |
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return(list); \ |
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} \ |
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\ |
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static type *CAT(name,_merge)(type *list1, type *list2, int (*cmp)(type *, type *));\ |
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\ |
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/* Merge the two lists list1 and list2, keeping the resulting |
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* list in order with respect to comparison function cmp (see |
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* above for specification of cmp. |
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* Return a pointer to the merged list. |
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*/ \ |
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static type *CAT(name,_merge)(register type *list1,register type *list2, \ |
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int (*cmp)(type *, type *)) \ |
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{ \ |
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register type *list, *head; \ |
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\ |
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if ((*cmp)(list1, list2) < 0) { \ |
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list = list1; \ |
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list1 = list1->next; \ |
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} \ |
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else { \ |
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list = list2; \ |
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list2 = list2->next; \ |
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} \ |
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head = list; \ |
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while (list1 != NULL && list2 != NULL) { \ |
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if ((*cmp)(list1, list2) < 0) { \ |
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list->next = list1; \ |
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list1 = list1->next; \ |
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} \ |
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else { \ |
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list->next = list2; \ |
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list2 = list2->next; \ |
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} \ |
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list = list->next; \ |
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} \ |
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list->next = (list1 != NULL) ? list1 : list2; \ |
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return(head); \ |
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} \ |
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\ |
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storageclass type *name(type *list, int len, int (*cmp)(type *, type *));\ |
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\ |
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storageclass type *name(type *list,int len, int (*cmp)(type *, type *)) \ |
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{ \ |
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type *list2; \ |
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\ |
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if (len > 1) { \ |
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list2 = CAT(name,_split)(list,len/2); \ |
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list = name(list,len/2,cmp); \ |
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list2 = name(list2,(len+1)/2,cmp); \ |
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return(CAT(name,_merge)(list,list2,cmp)); \ |
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} \ |
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else \ |
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return(list); \ |
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} |