max planck institut
informatik

# MPI-I-92-141

## Waste makes haste: tight bounds for loose parallel sorting

### Hagerup, Torben and Raman, Rajeev

MPI-I-92-141. September 1992, 185 pages. | Status: available - back from printing | Next --> Entry | Previous <-- Entry

Abstract in LaTeX format:
Conventional
parallel sorting requires the $n$ input
keys to be output in an array of size $n$, and is known to
take $\Omega({{\log n}/{\log\log n}})$ time using
any polynomial number of processors.
The lower bound does not apply to the more wasteful''
convention of {\em padded sorting}, which
requires the keys to be output in sorted order in
an array of size $(1 + o(1)) n$.
We give very fast randomized CRCW PRAM algorithms for
several padded-sorting problems.

Applying only pairwise comparisons to the input
and using $kn$ processors, where $2\le k\le n$,
we can padded-sort $n$ keys in
$O({{\log n}/{\log k}})$ time with
high probability (whp), which
is the best possible (expected)
run time for any comparison-based algorithm.
We also show how to padded-sort
$n$ independent random numbers
in $O(\log^*\! n)$ time whp with $O(n)$ work,
which matches a recent lower bound,
and how to padded-sort
$n$ integers in the range $1..n$
in constant time whp using $n$ processors.
If the integer sorting is required to be stable,
we can still solve the problem in
$O({{\log\log n}/{\log k}})$ time whp using
$kn$ processors, for any $k$ with $2\le k\le\log n$.
The integer sorting results require the
nonstandard OR PRAM; alternative implementations
on standard PRAM variants run in $O(\log\log n)$ time whp.
As an application of our padded-sorting algorithms,
we can solve approximate prefix summation problems
of size~$n$ with $O(n)$ work
in constant time whp on the OR PRAM,
and in $O(\log\log n)$ time whp on
standard PRAM variants.
Acknowledgement:
References to related material:

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URL to this document: http://domino.mpi-inf.mpg.de/internet/reports.nsf/NumberView/1992-141
BibTeX
@TECHREPORT{HagerupRaman92,
AUTHOR = {Hagerup, Torben and Raman, Rajeev},
TITLE = {Waste makes haste: tight bounds for loose parallel sorting},
TYPE = {Research Report},
INSTITUTION = {Max-Planck-Institut f{\"u}r Informatik},
ADDRESS = {Im Stadtwald, D-66123 Saarbr{\"u}cken, Germany},
NUMBER = {MPI-I-92-141},
MONTH = {September},
YEAR = {1992},
ISSN = {0946-011X},
}