## LIBRARY

Lb libbsd## SYNOPSIS

In bsd/stdlib.h Ft int Fo heapsort Fa void *base Fa size_t nmemb Fa size_t size Fa int *comparconst void *, const void * Fc Ft int Fo mergesort Fa void *base Fa size_t nmemb Fa size_t size Fa int *comparconst void *, const void * Fc## DESCRIPTION

The Fn heapsort function is a modified selection sort. The Fn mergesort function is a modified merge sort with exponential search intended for sorting data with pre-existing order.
The
Fn heapsort
function sorts an array of
Fa nmemb
objects, the initial member of which is pointed to by
Fa base .
The size of each object is specified by
Fa size .
The
Fn mergesort
function
behaves similarly, but
*requires*
that
Fa size
be greater than
``sizeof(void *) / 2''

The contents of the array Fa base are sorted in ascending order according to a comparison function pointed to by Fa 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
Fn heapsort
is
*not*
stable, that is, if two members compare as equal, their order in
the sorted array is undefined.
The
Fn mergesort
algorithm is stable.

The
Fn heapsort
function is an implementation of
An J.W.J. William Ns 's
``heapsort''
algorithm,
a variant of selection sorting; in particular, see
An D.E. Knuth Ns 's
*"Algorithm H" .*
**Heapsort**
takes O N lg N worst-case time.
Its
*only*
advantage over
Fn qsort
is that it uses almost no additional memory; while
Fn qsort
does not allocate memory, it is implemented using recursion.

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

## RETURN VALUES

Rv -std heapsort mergesort## ERRORS

The Fn heapsort and Fn mergesort functions succeed unless:**Bq**Er EINVAL- The Fa size argument is zero, or, the Fa size argument to Fn mergesort is less than ``sizeof(void *) / 2''
**Bq**Er ENOMEM- The Fn heapsort or Fn mergesort functions were unable to allocate memory.