297 lines
10 KiB
Groff
297 lines
10 KiB
Groff
.\" $NetBSD: openssl_lhash.3,v 1.2 2002/02/07 07:00:44 ross Exp $
|
|
.\"
|
|
.\" Automatically generated by Pod::Man version 1.02
|
|
.\" Thu Apr 12 19:27:13 2001
|
|
.\"
|
|
.\" Standard preamble:
|
|
.\" ======================================================================
|
|
.de Sh \" Subsection heading
|
|
.br
|
|
.if t .Sp
|
|
.ne 5
|
|
.PP
|
|
\fB\\$1\fR
|
|
.PP
|
|
..
|
|
.de Sp \" Vertical space (when we can't use .PP)
|
|
.if t .sp .5v
|
|
.if n .sp
|
|
..
|
|
.de Ip \" List item
|
|
.br
|
|
.ie \\n(.$>=3 .ne \\$3
|
|
.el .ne 3
|
|
.IP "\\$1" \\$2
|
|
..
|
|
.de Vb \" Begin verbatim text
|
|
.ft CW
|
|
.nf
|
|
.ne \\$1
|
|
..
|
|
.de Ve \" End verbatim text
|
|
.ft R
|
|
|
|
.fi
|
|
..
|
|
.\" Set up some character translations and predefined strings. \*(-- will
|
|
.\" give an unbreakable dash, \*(PI will give pi, \*(L" will give a left
|
|
.\" double quote, and \*(R" will give a right double quote. | will give a
|
|
.\" real vertical bar. \*(C+ will give a nicer C++. Capital omega is used
|
|
.\" to do unbreakable dashes and therefore won't be available. \*(C` and
|
|
.\" \*(C' expand to `' in nroff, nothing in troff, for use with C<>
|
|
.tr \(*W-|\(bv\*(Tr
|
|
.ds C+ C\v'-.1v'\h'-1p'\s-2+\h'-1p'+\s0\v'.1v'\h'-1p'
|
|
.ie n \{\
|
|
. ds -- \(*W-
|
|
. ds PI pi
|
|
. if (\n(.H=4u)&(1m=24u) .ds -- \(*W\h'-12u'\(*W\h'-12u'-\" diablo 10 pitch
|
|
. if (\n(.H=4u)&(1m=20u) .ds -- \(*W\h'-12u'\(*W\h'-8u'-\" diablo 12 pitch
|
|
. ds L" ""
|
|
. ds R" ""
|
|
. ds C` `
|
|
. ds C' '
|
|
'br\}
|
|
.el\{\
|
|
. ds -- \|\(em\|
|
|
. ds PI \(*p
|
|
. ds L" ``
|
|
. ds R" ''
|
|
'br\}
|
|
.\"
|
|
.\" If the F register is turned on, we'll generate index entries on stderr
|
|
.\" for titles (.TH), headers (.SH), subsections (.Sh), items (.Ip), and
|
|
.\" index entries marked with X<> in POD. Of course, you'll have to process
|
|
.\" the output yourself in some meaningful fashion.
|
|
.if \nF \{\
|
|
. de IX
|
|
. tm Index:\\$1\t\\n%\t"\\$2"
|
|
. .
|
|
. nr % 0
|
|
. rr F
|
|
.\}
|
|
.\"
|
|
.\" For nroff, turn off justification. Always turn off hyphenation; it
|
|
.\" makes way too many mistakes in technical documents.
|
|
.hy 0
|
|
.if n .na
|
|
.\"
|
|
.\" Accent mark definitions (@(#)ms.acc 1.5 88/02/08 SMI; from UCB 4.2).
|
|
.\" Fear. Run. Save yourself. No user-serviceable parts.
|
|
.bd B 3
|
|
. \" fudge factors for nroff and troff
|
|
.if n \{\
|
|
. ds #H 0
|
|
. ds #V .8m
|
|
. ds #F .3m
|
|
. ds #[ \f1
|
|
. ds #] \fP
|
|
.\}
|
|
.if t \{\
|
|
. ds #H ((1u-(\\\\n(.fu%2u))*.13m)
|
|
. ds #V .6m
|
|
. ds #F 0
|
|
. ds #[ \&
|
|
. ds #] \&
|
|
.\}
|
|
. \" simple accents for nroff and troff
|
|
.if n \{\
|
|
. ds ' \&
|
|
. ds ` \&
|
|
. ds ^ \&
|
|
. ds , \&
|
|
. ds ~ ~
|
|
. ds /
|
|
.\}
|
|
.if t \{\
|
|
. ds ' \\k:\h'-(\\n(.wu*8/10-\*(#H)'\'\h"|\\n:u"
|
|
. ds ` \\k:\h'-(\\n(.wu*8/10-\*(#H)'\`\h'|\\n:u'
|
|
. ds ^ \\k:\h'-(\\n(.wu*10/11-\*(#H)'^\h'|\\n:u'
|
|
. ds , \\k:\h'-(\\n(.wu*8/10)',\h'|\\n:u'
|
|
. ds ~ \\k:\h'-(\\n(.wu-\*(#H-.1m)'~\h'|\\n:u'
|
|
. ds / \\k:\h'-(\\n(.wu*8/10-\*(#H)'\z\(sl\h'|\\n:u'
|
|
.\}
|
|
. \" troff and (daisy-wheel) nroff accents
|
|
.ds : \\k:\h'-(\\n(.wu*8/10-\*(#H+.1m+\*(#F)'\v'-\*(#V'\z.\h'.2m+\*(#F'.\h'|\\n:u'\v'\*(#V'
|
|
.ds 8 \h'\*(#H'\(*b\h'-\*(#H'
|
|
.ds o \\k:\h'-(\\n(.wu+\w'\(de'u-\*(#H)/2u'\v'-.3n'\*(#[\z\(de\v'.3n'\h'|\\n:u'\*(#]
|
|
.ds d- \h'\*(#H'\(pd\h'-\w'~'u'\v'-.25m'\f2\(hy\fP\v'.25m'\h'-\*(#H'
|
|
.ds D- D\\k:\h'-\w'D'u'\v'-.11m'\z\(hy\v'.11m'\h'|\\n:u'
|
|
.ds th \*(#[\v'.3m'\s+1I\s-1\v'-.3m'\h'-(\w'I'u*2/3)'\s-1o\s+1\*(#]
|
|
.ds Th \*(#[\s+2I\s-2\h'-\w'I'u*3/5'\v'-.3m'o\v'.3m'\*(#]
|
|
.ds ae a\h'-(\w'a'u*4/10)'e
|
|
.ds Ae A\h'-(\w'A'u*4/10)'E
|
|
. \" corrections for vroff
|
|
.if v .ds ~ \\k:\h'-(\\n(.wu*9/10-\*(#H)'\s-2\u~\d\s+2\h'|\\n:u'
|
|
.if v .ds ^ \\k:\h'-(\\n(.wu*10/11-\*(#H)'\v'-.4m'^\v'.4m'\h'|\\n:u'
|
|
. \" for low resolution devices (crt and lpr)
|
|
.if \n(.H>23 .if \n(.V>19 \
|
|
\{\
|
|
. ds : e
|
|
. ds 8 ss
|
|
. ds o a
|
|
. ds d- d\h'-1'\(ga
|
|
. ds D- D\h'-1'\(hy
|
|
. ds th \o'bp'
|
|
. ds Th \o'LP'
|
|
. ds ae ae
|
|
. ds Ae AE
|
|
.\}
|
|
.rm #[ #] #H #V #F C
|
|
.\" ======================================================================
|
|
.\"
|
|
.IX Title "lhash 3"
|
|
.TH lhash 3 "0.9.6a" "2001-04-12" "OpenSSL"
|
|
.UC
|
|
.SH "NAME"
|
|
lh_new, lh_free, lh_insert, lh_delete, lh_retrieve, lh_doall,
|
|
lh_doall_arg, lh_error \- dynamic hash table
|
|
.SH "LIBRARY"
|
|
libcrypto, -lcrypto
|
|
.SH "SYNOPSIS"
|
|
.IX Header "SYNOPSIS"
|
|
.Vb 1
|
|
\& #include \*[Lt]openssl/lhash.h\*[Gt]
|
|
.Ve
|
|
.Vb 3
|
|
\& LHASH *lh_new(unsigned long (*hash)(/*void *a*/),
|
|
\& int (*compare)(/*void *a,void *b*/));
|
|
\& void lh_free(LHASH *table);
|
|
.Ve
|
|
.Vb 3
|
|
\& void *lh_insert(LHASH *table, void *data);
|
|
\& void *lh_delete(LHASH *table, void *data);
|
|
\& void *lh_retrieve(LHASH *table, void *data);
|
|
.Ve
|
|
.Vb 3
|
|
\& void lh_doall(LHASH *table, void (*func)(/*void *b*/));
|
|
\& void lh_doall_arg(LHASH *table, void (*func)(/*void *a,void *b*/),
|
|
\& void *arg);
|
|
.Ve
|
|
.Vb 1
|
|
\& int lh_error(LHASH *table);
|
|
.Ve
|
|
.SH "DESCRIPTION"
|
|
.IX Header "DESCRIPTION"
|
|
This library implements dynamic hash tables. The hash table entries
|
|
can be arbitrary structures. Usually they consist of key and value
|
|
fields.
|
|
.PP
|
|
\&\fIlh_new()\fR creates a new \fB\s-1LHASH\s0\fR structure. \fBhash\fR takes a pointer to
|
|
the structure and returns an unsigned long hash value of its key
|
|
field. The hash value is normally truncated to a power of 2, so make
|
|
sure that your hash function returns well mixed low order
|
|
bits. \fBcompare\fR takes two arguments, and returns 0 if their keys are
|
|
equal, non-zero otherwise.
|
|
.PP
|
|
\&\fIlh_free()\fR frees the \fB\s-1LHASH\s0\fR structure \fBtable\fR. Allocated hash table
|
|
entries will not be freed; consider using \fIlh_doall()\fR to deallocate any
|
|
remaining entries in the hash table.
|
|
.PP
|
|
\&\fIlh_insert()\fR inserts the structure pointed to by \fBdata\fR into \fBtable\fR.
|
|
If there already is an entry with the same key, the old value is
|
|
replaced. Note that \fIlh_insert()\fR stores pointers, the data are not
|
|
copied.
|
|
.PP
|
|
\&\fIlh_delete()\fR deletes an entry from \fBtable\fR.
|
|
.PP
|
|
\&\fIlh_retrieve()\fR looks up an entry in \fBtable\fR. Normally, \fBdata\fR is
|
|
a structure with the key \fIfield\fR\|(s) set; the function will return a
|
|
pointer to a fully populated structure.
|
|
.PP
|
|
\&\fIlh_doall()\fR will, for every entry in the hash table, call \fBfunc\fR with
|
|
the data item as parameters.
|
|
This function can be quite useful when used as follows:
|
|
void cleanup(\s-1STUFF\s0 *a)
|
|
{ \fISTUFF_free\fR\|(a); }
|
|
lh_doall(hash,cleanup);
|
|
lh_free(hash);
|
|
This can be used to free all the entries. \fIlh_free()\fR then cleans up the
|
|
\&'buckets' that point to nothing. When doing this, be careful if you
|
|
delete entries from the hash table in \fBfunc\fR: the table may decrease
|
|
in size, moving item that you are currently on down lower in the hash
|
|
table. This could cause some entries to be skipped. The best
|
|
solution to this problem is to set hash-\*[Gt]down_load=0 before you
|
|
start. This will stop the hash table ever being decreased in size.
|
|
.PP
|
|
\&\fIlh_doall_arg()\fR is the same as \fIlh_doall()\fR except that \fBfunc\fR will
|
|
be called with \fBarg\fR as the second argument.
|
|
.PP
|
|
\&\fIlh_error()\fR can be used to determine if an error occurred in the last
|
|
operation. \fIlh_error()\fR is a macro.
|
|
.SH "RETURN VALUES"
|
|
.IX Header "RETURN VALUES"
|
|
\&\fIlh_new()\fR returns \fB\s-1NULL\s0\fR on error, otherwise a pointer to the new
|
|
\&\fB\s-1LHASH\s0\fR structure.
|
|
.PP
|
|
When a hash table entry is replaced, \fIlh_insert()\fR returns the value
|
|
being replaced. \fB\s-1NULL\s0\fR is returned on normal operation and on error.
|
|
.PP
|
|
\&\fIlh_delete()\fR returns the entry being deleted. \fB\s-1NULL\s0\fR is returned if
|
|
there is no such value in the hash table.
|
|
.PP
|
|
\&\fIlh_retrieve()\fR returns the hash table entry if it has been found,
|
|
\&\fB\s-1NULL\s0\fR otherwise.
|
|
.PP
|
|
\&\fIlh_error()\fR returns 1 if an error occurred in the last operation, 0
|
|
otherwise.
|
|
.PP
|
|
\&\fIlh_free()\fR, \fIlh_doall()\fR and \fIlh_doall_arg()\fR return no values.
|
|
.SH "BUGS"
|
|
.IX Header "BUGS"
|
|
\&\fIlh_insert()\fR returns \fB\s-1NULL\s0\fR both for success and error.
|
|
.SH "INTERNALS"
|
|
.IX Header "INTERNALS"
|
|
The following description is based on the SSLeay documentation:
|
|
.PP
|
|
The \fBlhash\fR library implements a hash table described in the
|
|
\&\fICommunications of the \s-1ACM\s0\fR in 1991. What makes this hash table
|
|
different is that as the table fills, the hash table is increased (or
|
|
decreased) in size via \fIOPENSSL_realloc()\fR. When a 'resize' is done, instead of
|
|
all hashes being redistributed over twice as many 'buckets', one
|
|
bucket is split. So when an 'expand' is done, there is only a minimal
|
|
cost to redistribute some values. Subsequent inserts will cause more
|
|
single 'bucket' redistributions but there will never be a sudden large
|
|
cost due to redistributing all the 'buckets'.
|
|
.PP
|
|
The state for a particular hash table is kept in the \fB\s-1LHASH\s0\fR structure.
|
|
The decision to increase or decrease the hash table size is made
|
|
depending on the 'load' of the hash table. The load is the number of
|
|
items in the hash table divided by the size of the hash table. The
|
|
default values are as follows. If (hash-\*[Gt]up_load \*[Lt] load) =\*[Gt]
|
|
expand. if (hash-\*[Gt]down_load \*[Gt] load) =\*[Gt] contract. The
|
|
\&\fBup_load\fR has a default value of 1 and \fBdown_load\fR has a default value
|
|
of 2. These numbers can be modified by the application by just
|
|
playing with the \fBup_load\fR and \fBdown_load\fR variables. The 'load' is
|
|
kept in a form which is multiplied by 256. So
|
|
hash-\*[Gt]up_load=8*256; will cause a load of 8 to be set.
|
|
.PP
|
|
If you are interested in performance the field to watch is
|
|
num_comp_calls. The hash library keeps track of the 'hash' value for
|
|
each item so when a lookup is done, the 'hashes' are compared, if
|
|
there is a match, then a full compare is done, and
|
|
hash-\*[Gt]num_comp_calls is incremented. If num_comp_calls is not equal
|
|
to num_delete plus num_retrieve it means that your hash function is
|
|
generating hashes that are the same for different values. It is
|
|
probably worth changing your hash function if this is the case because
|
|
even if your hash table has 10 items in a 'bucket', it can be searched
|
|
with 10 \fBunsigned long\fR compares and 10 linked list traverses. This
|
|
will be much less expensive that 10 calls to you compare function.
|
|
.PP
|
|
\&\fIlh_strhash()\fR is a demo string hashing function:
|
|
.PP
|
|
.Vb 1
|
|
\& unsigned long lh_strhash(const char *c);
|
|
.Ve
|
|
Since the \fB\s-1LHASH\s0\fR routines would normally be passed structures, this
|
|
routine would not normally be passed to \fIlh_new()\fR, rather it would be
|
|
used in the function passed to \fIlh_new()\fR.
|
|
.SH "SEE ALSO"
|
|
.IX Header "SEE ALSO"
|
|
lh_stats(3)
|
|
.SH "HISTORY"
|
|
.IX Header "HISTORY"
|
|
The \fBlhash\fR library is available in all versions of SSLeay and OpenSSL.
|
|
\&\fIlh_error()\fR was added in SSLeay 0.9.1b.
|
|
.PP
|
|
This manpage is derived from the SSLeay documentation.
|