MirOS Manual: heapsort(3), mergesort(3), qsort(3)

QSORT(3)                   BSD Programmer's Manual                    QSORT(3)

NAME

     qsort, heapsort, mergesort - sort functions

SYNOPSIS

     #include <stdlib.h>

     void
     qsort(void *base, size_t nmemb, size_t size,
             int (*compar)(const void *, const void *));

     int
     heapsort(void *base, size_t nmemb, size_t size,
             int (*compar)(const void *, const void *));

     int
     mergesort(void *base, size_t nmemb, size_t size,
             int (*compar)(const void *, const void *));

DESCRIPTION

     The qsort() function is a modified partition-exchange sort, or quicksort.
     The heapsort() function is a modified selection sort. The mergesort()
     function is a modified merge sort with exponential search intended for
     sorting data with pre-existing order.

     The qsort() and heapsort() functions sort an array of nmemb objects, the
     initial member of which is pointed to by base. The size of each object is
     specified by size. mergesort() behaves similarly, but requires that size
     be greater than "sizeof(void *) / 2".

     The contents of the array base are sorted in ascending order according to
     a comparison function pointed to by compar, which requires two arguments
     pointing to the objects being compared.

     The comparison function must return an integer less than, equal to, or
     greater than zero if the first argument is considered to be respectively
     less than, equal to, or greater than the second.

     The functions qsort() and heapsort() are not stable, that is, if two
     members compare as equal, their order in the sorted array is undefined.
     The function mergesort() is stable.

     The qsort() function is an implementation of C.A.R. Hoare's "quicksort"
     algorithm, a variant of partition-exchange sorting; in particular, see
     D.E. Knuth's Algorithm Q. qsort() takes O N lg N average time. This im-
     plementation uses median selection to avoid its O N**2 worst-case
     behavior.

     The heapsort() function is an implementation of J.W.J. William's
     "heapsort" algorithm, a variant of selection sorting; in particular, see
     D.E. Knuth's Algorithm H. heapsort() takes O N lg N worst-case time. This
     implementation of heapsort() is implemented without recursive function
     calls.

     The function mergesort() requires additional memory of size nmemb * size
     bytes; it should be used only when space is not at a premium. mergesort()
     is optimized for data with pre-existing order; its worst case time is O N
     lg N; its best case is O N.

     Normally, qsort() is faster than mergesort(), which is faster than heap-
     sort(). Memory availability and pre-existing order in the data can make
     this untrue.

RETURN VALUES

     The qsort() function returns no value.
     Upon successful completion, heapsort() and mergesort() return 0. Other-
     wise, they return -1 and the global variable errno is set to indicate the
     error.

ERRORS

     The heapsort() and mergesort() functions succeed unless:

     [EINVAL]      The size argument is zero, or the size argument to mer-
                   gesort() is less than "sizeof(void *) / 2".

     [ENOMEM]      heapsort() or mergesort() were unable to allocate memory.

SEE ALSO

     sort(1), radixsort(3)

     Hoare, C.A.R., "Quicksort", The Computer Journal, 5:1, pp. 10-15, 1962.

     Williams, J.W.J, "Heapsort", Communications of the ACM, 7:1, pp. 347-348,
     1964.

     Knuth, D.E., "Sorting and Searching", The Art of Computer Programming,
     Vol. 3, pp. 114-123, 145-149, 1968.

     McIlroy, P.M., "Optimistic Sorting and Information Theoretic Complexity",
     Fourth Annual ACM-SIAM Symposium on Discrete Algorithms, pp. 467-464,
     January 1993.

     Bentley, J.L. and McIlroy, M.D., "Engineering a Sort Function", Software
     - Practice and Experience, Vol. 23(11), pp. 1249-1265, November 1993.

STANDARDS

     Previous versions of qsort() did not permit the comparison routine itself
     to call qsort(). This is no longer true.

     The qsort() function conforms to ANSI X3.159-1989 ("ANSI C").

MirOS BSD #10-current            June 4, 1993                                1

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