mergesort(3) [debian man page]

QSORT(3)						   BSD Library Functions Manual 						  QSORT(3)

NAME

     heapsort, mergesort -- sort functions

LIBRARY

     Utility functions from BSD systems (libbsd, -lbsd)

SYNOPSIS

     #include <bsd/stdlib.h>

     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 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 heapsort() function sorts an array of nmemb objects, the initial member of which is pointed to by base.  The size of each object is spec-
     ified by size.  The mergesort() function 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 respec-
     tively less than, equal to, or greater than the second.

     The algorithm implemented by heapsort() is not stable, that is, if two members compare as equal, their order in the sorted array is unde-
     fined.  The mergesort() algorithm is stable.

     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.  Its only advantage over qsort() is that it uses almost no additional
     memory; while qsort() does not allocate memory, it is implemented using recursion.

     The function mergesort() requires additional memory of size nmemb * size bytes; it should be used only when space is not at a premium.  The
     mergesort() function 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() is faster than heapsort().  Memory availability and pre-existing order in the data can make this
     untrue.

RETURN VALUES

     The heapsort() and mergesort() functions return the value 0 if successful; otherwise the value -1 is returned 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 mergesort() is less than ``sizeof(void *) / 2''.

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

SEE ALSO

     sort(1), radixsort(3)

     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, January
     1992.

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

BSD
								September 30, 2003							       BSD

QSORT(3)						   BSD Library Functions Manual 						  QSORT(3)

NAME

     qsort, heapsort, mergesort -- sort functions

LIBRARY

     Standard C Library (libc, -lc)

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 respec-
     tively 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 implementation 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.  Its only advantage over qsort() is that it uses almost no additional
     memory; while qsort() does not allocate memory, it is implemented using recursion.

     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() is faster than heapsort().  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.  Otherwise, they return -1 and the global variable errno is set to indicate
     the error.

ERRORS

     The heapsort() function succeeds unless:

     [EINVAL]		The size argument is zero, or, the size argument to mergesort() is less than ``sizeof(void *) / 2''.

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

COMPATIBILITY

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

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", Proceedings of the Fourth Annual ACM-SIAM Symposium on Discrete
     Algorithms, pp. 467-474, 1993.

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

STANDARDS

     The qsort() function conforms to ANSI X3.159-1989 (``ANSI C89'').

BSD
								   June 4, 1993 							       BSD