radixsort
,
sradixsort
—
radix sort
Standard C Library (libc, -lc)
#include
<limits.h>
#include
<stdlib.h>
int
radixsort
(
const
unsigned char **base,
int nmemb,
const unsigned char
*table,
unsigned
endbyte);
int
sradixsort
(
const
unsigned char **base,
int nmemb,
const unsigned char
*table,
unsigned
endbyte);
The
radixsort
() and
sradixsort
() functions are implementations
of radix sort.
These functions sort an array of pointers to byte strings, the initial member of
which is referenced by
base. The byte strings
may contain any values; the end of each string is denoted by the
user-specified value
endbyte.
Applications may specify a sort order by providing the
table argument. If
non-
NULL
,
table must reference an array of
UCHAR_MAX
+ 1 bytes which contains the sort
weight of each possible byte value. The end-of-string byte must have a sort
weight of 0 or 255 (for sorting in reverse order). More than one byte may have
the same sort weight. The
table argument is
useful for applications which wish to sort different characters equally, for
example, providing a table with the same weights for A-Z as for a-z will
result in a case-insensitive sort. If
table
is NULL, the contents of the array are sorted in ascending order according to
the ASCII order of the byte strings they reference and
endbyte has a sorting weight of 0.
The
sradixsort
() function is stable, that is,
if two elements compare as equal, their order in the sorted array is
unchanged. The
sradixsort
() function uses
additional memory sufficient to hold
nmemb
pointers.
The
radixsort
() function is not stable, but
uses no additional memory.
These functions are variants of most-significant-byte radix sorting; in
particular, see
D.E. Knuth's
Algorithm R and section 5.2.5, exercise 10. They take
linear time relative to the number of bytes in the strings.
The
radixsort
() function returns the
value 0 if successful; otherwise the value -1 is returned and
the global variable
errno is set to indicate
the error.
- [
EINVAL
]
- The value of the endbyte element of
table is not 0 or 255.
Additionally, the
sradixsort
() function may
fail and set
errno for any of the errors
specified for the library routine
malloc(3).
sort(1),
qsort(3)
Knuth, D.E.,
Sorting and Searching, The Art of
Computer Programming, Vol. 3,
pp. 170-178, 1968.
Paige, R.,
Three Partition Refinement Algorithms,
SIAM J. Comput., No. 6,
Vol. 16, 1987.
McIlroy, P.,
Computing Systems, Engineering Radix
Sort, Vol. 6:1, pp.
5-27, 1993.
The
radixsort
() function first appeared in
4.4BSD.