heapsort(3bsd) | 3bsd | heapsort(3bsd) |

# NAME

`heapsort`

,
`mergesort`

— sort
functions

# LIBRARY

library “libbsd”

# SYNOPSIS

```
#include
<stdlib.h>
```

(See
libbsd(7) for include usage.)

`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 specified 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 respectively 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 undefined. 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:

# SEE ALSO

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.

September 30, 2003 | Linux 6.8.7-arch1-1 |