minix/usr.bin/nbperf/nbperf.1
Lionel Sambuc 84d9c625bf Synchronize on NetBSD-CVS (2013/12/1 12:00:00 UTC)
- Fix for possible unset uid/gid in toproto
 - Fix for default mtree style
 - Update libelf
 - Importing libexecinfo
 - Resynchronize GCC, mpc, gmp, mpfr
 - build.sh: Replace params with show-params.
     This has been done as the make target has been renamed in the same
     way, while a new target named params has been added. This new
     target generates a file containing all the parameters, instead of
     printing it on the console.
 - Update test48 with new etc/services (Fix by Ben Gras <ben@minix3.org)
     get getservbyport() out of the inner loop

Change-Id: Ie6ad5226fa2621ff9f0dee8782ea48f9443d2091
2014-07-28 17:05:06 +02:00

143 lines
4.2 KiB
Groff

.\" $NetBSD: nbperf.1,v 1.6 2013/01/31 16:32:02 joerg Exp $
.\"
.\" Copyright (c) 2009 The NetBSD Foundation, Inc.
.\" All rights reserved.
.\"
.\" This code is derived from software contributed to The NetBSD Foundation
.\" by Joerg Sonnenberger.
.\"
.\" Redistribution and use in source and binary forms, with or without
.\" modification, are permitted provided that the following conditions
.\" are met:
.\" 1. Redistributions of source code must retain the above copyright
.\" notice, this list of conditions and the following disclaimer.
.\" 2. Redistributions in binary form must reproduce the above copyright
.\" notice, this list of conditions and the following disclaimer in the
.\" documentation and/or other materials provided with the distribution.
.\"
.\" THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS
.\" ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
.\" TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
.\" PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS
.\" BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
.\" CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
.\" SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
.\" INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
.\" CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
.\" ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
.\" POSSIBILITY OF SUCH DAMAGE.
.\"
.Dd September 25, 2012
.Dt NBPERF 1
.Os
.Sh NAME
.Nm nbperf
.Nd compute a perfect hash function
.Sh SYNOPSIS
.Nm
.Op Fl ps
.Op Fl a Ar algorithm
.Op Fl c Ar utilisation
.Op Fl h Ar hash
.Op Fl i Ar iterations
.Op Fl m Ar map-file
.Op Fl n Ar name
.Op Fl o Ar output
.Op Ar input
.Sh DESCRIPTION
.Nm
reads a number of keys one per line from standard input or
.Ar input .
It computes a minimal perfect hash function and writes it to stdout or
.Ar output .
The default algorithm is
.Qq Sy chm .
.Pp
The
.Fl m
argument instructs
.Nm
to write the resulting key mapping to
.Ar map-file .
Each line gives the result of the hash function for the corresponding input
key.
.Pp
The parameter
.Ar utilisation
determines the space efficiency.
.Pp
Supported arguments for
.Fl a :
.Bl -tag -width "chm"
.It Sy chm
This results in an order preserving minimal perfect hash function.
The
.Ar utilisation
must be at least 2, the default.
The number of iterations needed grows if the utilisation is very near to 2.
.It Sy chm3
Similar to
.Ar chm .
The resulting hash function needs three instead of two table lookups when
compared to
.Ar chm .
The
.Ar utilisation
must be at least 1.24, the default.
This makes the output for
.Ar chm3
noticable smaller than the output for
.Ar chm .
.It Sy bpz
This results in a non-order preserving minimal perfect hash function.
Output size is approximately 2.79 bit per key for the default value of
.Ar utilisation ,
1.24.
This is also the smallest supported value.
.El
.Pp
Supported arguments for
.Fl h :
.Bl -tag -width "mi_vector_hash"
.It Sy mi_vector_hash
Platform-independent version of Jenkins parallel hash.
See
.Xr mi_vector_hash 3 .
.El
.Pp
The number of iterations can be limited with
.Fl i .
.Nm
outputs a function matching
.Ft uint32_t
.Fn hash "const void * restrict" "size_t"
to stdout.
The function expects the key length as second argument, for strings not
including the terminating NUL.
It is the responsibility of the caller to pass in only valid keys or compare
the resulting index to the key.
The function name can be changed using
.Fl n Ar name .
If the
.Fl s
flag is specified, it will be static.
.Pp
After each failing iteration, a dot is written to stderr.
.Pp
.Nm
checks for duplicate keys on the first iteration that passed
basic hash distribution tests.
In that case, an error message is printed and the program terminates.
.Pp
If the
.Fl p
flag is specified, the hash function is seeded in a stable way.
This may take longer than the normal random seed, but ensures
that the output is the same for repeated invocations as long as
the input is constant.
.Sh EXIT STATUS
.Ex -std
.Sh SEE ALSO
.Xr mi_vector_hash 3
.Sh AUTHORS
.An J\(:org Sonnenberger