356 lines
11 KiB
Groff
356 lines
11 KiB
Groff
.rn '' }`
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'''
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'''
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.de Sh
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.br
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.if t .Sp
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.ne 5
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.PP
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\fB\\$1\fR
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.PP
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..
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.de Sp
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.if t .sp .5v
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.if n .sp
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..
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.de Ip
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.br
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.ie \\n(.$>=3 .ne \\$3
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.el .ne 3
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.IP "\\$1" \\$2
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.de Vb
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.ft CW
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.nf
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.ft R
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..
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'''
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'''
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''' Set up \*(-- to give an unbreakable dash;
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''' string Tr holds user defined translation string.
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''' Bell System Logo is used as a dummy character.
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'''
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.tr \(*W-|\(bv\*(Tr
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.ie n \{\
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.ds -- \(*W-
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.ds PI pi
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.if (\n(.H=4u)&(1m=24u) .ds -- \(*W\h'-12u'\(*W\h'-12u'-\" diablo 10 pitch
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.ds L" ""
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''' \*(M", \*(S", \*(N" and \*(T" are the equivalent of
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''' \*(L" and \*(R", except that they are used on ".xx" lines,
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''' such as .IP and .SH, which do another additional levels of
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''' double-quote interpretation
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.ds M" """
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'br\}
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.el\{\
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.ds -- \(em\|
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.tr \*(Tr
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.ds L" ``
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.ds PI \(*p
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'br\}
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.\" If the F register is turned on, we'll generate
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.\" index entries out stderr for the following things:
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.\" TH Title
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.\" SH Header
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.\" Sh Subsection
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.\" Ip Item
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.\" X<> Xref (embedded
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.\" Of course, you have to process the output yourself
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.\" in some meaninful fashion.
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.if \nF \{
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.de IX
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.tm Index:\\$1\t\\n%\t"\\$2"
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..
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.nr % 0
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.rr F
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.\}
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.TH lhash 3 "0.9.5a" "22/Jul/2000" "OpenSSL"
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.UC
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.if n .hy 0
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.if n .na
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.ds C+ C\v'-.1v'\h'-1p'\s-2+\h'-1p'+\s0\v'.1v'\h'-1p'
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.de CQ \" put $1 in typewriter font
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.ft CW
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'if n "\c
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'if t \\&\\$1\c
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'if n \\&\\$1\c
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'if n \&"
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\\&\\$2 \\$3 \\$4 \\$5 \\$6 \\$7
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'.ft R
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..
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.\" @(#)ms.acc 1.5 88/02/08 SMI; from UCB 4.2
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. \" AM - accent mark definitions
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.bd B 3
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. \" fudge factors for nroff and troff
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.if n \{\
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. ds #F .3m
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.\}
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.if t \{\
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. ds #H ((1u-(\\\\n(.fu%2u))*.13m)
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. ds #V .6m
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. ds #F 0
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. ds #] \&
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.\}
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. \" simple accents for nroff and troff
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.if n \{\
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. ds ' \&
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. ds ` \&
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. ds ^ \&
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. ds , \&
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. ds ~ ~
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.\}
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.if t \{\
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. ds ' \\k:\h'-(\\n(.wu*8/10-\*(#H)'\'\h"|\\n:u"
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. ds ` \\k:\h'-(\\n(.wu*8/10-\*(#H)'\`\h'|\\n:u'
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. ds , \\k:\h'-(\\n(.wu*8/10)',\h'|\\n:u'
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. ds ~ \\k:\h'-(\\n(.wu-\*(#H-.1m)'~\h'|\\n:u'
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. ds ? \s-2c\h'-\w'c'u*7/10'\u\h'\*(#H'\zi\d\s+2\h'\w'c'u*8/10'
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.\}
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.ds 8 \h'\*(#H'\(*b\h'-\*(#H'
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.ds _ \\k:\h'-(\\n(.wu*9/10-\*(#H+(\*(#F*2/3))'\v'-.4m'\z\(hy\v'.4m'\h'|\\n:u'
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.ds . \\k:\h'-(\\n(.wu*8/10)'\v'\*(#V*4/10'\z.\v'-\*(#V*4/10'\h'|\\n:u'
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.ds 3 \*(#[\v'.2m'\s-2\&3\s0\v'-.2m'\*(#]
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.ds o \\k:\h'-(\\n(.wu+\w'\(de'u-\*(#H)/2u'\v'-.3n'\*(#[\z\(de\v'.3n'\h'|\\n:u'\*(#]
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.ds d- \h'\*(#H'\(pd\h'-\w'~'u'\v'-.25m'\f2\(hy\fP\v'.25m'\h'-\*(#H'
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.ds D- D\\k:\h'-\w'D'u'\v'-.11m'\z\(hy\v'.11m'\h'|\\n:u'
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.ds th \*(#[\v'.3m'\s+1I\s-1\v'-.3m'\h'-(\w'I'u*2/3)'\s-1o\s+1\*(#]
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.ds Th \*(#[\s+2I\s-2\h'-\w'I'u*3/5'\v'-.3m'o\v'.3m'\*(#]
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.ds oe o\h'-(\w'o'u*4/10)'e
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. \" corrections for vroff
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.if v .ds ~ \\k:\h'-(\\n(.wu*9/10-\*(#H)'\s-2\u~\d\s+2\h'|\\n:u'
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.if v .ds ^ \\k:\h'-(\\n(.wu*10/11-\*(#H)'\v'-.4m'^\v'.4m'\h'|\\n:u'
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. \" for low resolution devices (crt and lpr)
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.if \n(.H>23 .if \n(.V>19 \
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\{\
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. ds 8 ss
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. ds v \h'-1'\o'\(aa\(ga'
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. ds . \h'-1'.
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.\}
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.rm #[ #] #H #V #F C
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.SH "NAME"
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lh_new, lh_free, lh_insert, lh_delete, lh_retrieve, lh_doall,
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lh_doall_arg, lh_error \- dynamic hash table
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.SH "LIBRARY"
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libcrypto, -lcrypto
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.SH "SYNOPSIS"
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.PP
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.Vb 1
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\& #include <openssl/lhash.h>
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.Ve
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.Vb 3
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\& LHASH *lh_new(unsigned long (*hash)(/*void *a*/),
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\& int (*compare)(/*void *a,void *b*/));
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\& void lh_free(LHASH *table);
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.Ve
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.Vb 3
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\& void *lh_insert(LHASH *table, void *data);
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\& void *lh_delete(LHASH *table, void *data);
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\& void *lh_retrieve(LHASH *table, void *data);
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.Ve
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.Vb 3
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\& void lh_doall(LHASH *table, void (*func)(/*void *b*/));
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\& void lh_doall_arg(LHASH *table, void (*func)(/*void *a,void *b*/),
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\& void *arg);
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.Ve
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.Vb 1
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\& int lh_error(LHASH *table);
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.Ve
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.SH "DESCRIPTION"
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This library implements dynamic hash tables. The hash table entries
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can be arbitrary structures. Usually they consist of key and value
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fields.
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.PP
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\fIlh_new()\fR creates a new \fBLHASH\fR structure. \fBhash\fR takes a pointer to
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the structure and returns an unsigned long hash value of its key
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field. The hash value is normally truncated to a power of 2, so make
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sure that your hash function returns well mixed low order
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bits. \fBcompare\fR takes two arguments, and returns 0 if their keys are
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equal, non-zero otherwise.
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.PP
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\fIlh_free()\fR frees the \fBLHASH\fR structure \fBtable\fR. Allocated hash table
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entries will not be freed; consider using \fIlh_doall()\fR to deallocate any
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remaining entries in the hash table.
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.PP
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\fIlh_insert()\fR inserts the structure pointed to by \fBdata\fR into \fBtable\fR.
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If there already is an entry with the same key, the old value is
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replaced. Note that \fIlh_insert()\fR stores pointers, the data are not
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copied.
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.PP
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\fIlh_delete()\fR deletes an entry from \fBtable\fR.
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.PP
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\fIlh_retrieve()\fR looks up an entry in \fBtable\fR. Normally, \fBdata\fR is
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a structure with the key \fIfield\fR\|(s) set; the function will return a
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pointer to a fully populated structure.
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.PP
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\fIlh_doall()\fR will, for every entry in the hash table, call \fBfunc\fR with
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the data item as parameters.
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This function can be quite useful when used as follows:
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void \fIcleanup\fR\|(STUFF *a)
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{ \fISTUFF_free\fR\|(a); }
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\fIlh_doall\fR\|(hash,cleanup);
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\fIlh_free\fR\|(hash);
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This can be used to free all the entries. \fIlh_free()\fR then cleans up the
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\&'buckets\*(R' that point to nothing. When doing this, be careful if you
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delete entries from the hash table in \fBfunc\fR: the table may decrease
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in size, moving item that you are currently on down lower in the hash
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table. This could cause some entries to be skipped. The best
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solution to this problem is to set hash->down_load=0 before you
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start. This will stop the hash table ever being decreased in size.
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.PP
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\fIlh_doall_arg()\fR is the same as \fIlh_doall()\fR except that \fBfunc\fR will
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be called with \fBarg\fR as the second argument.
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.PP
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\fIlh_error()\fR can be used to determine if an error occurred in the last
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operation. \fIlh_error()\fR is a macro.
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.SH "RETURN VALUES"
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\fIlh_new()\fR returns \fBNULL\fR on error, otherwise a pointer to the new
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\fBLHASH\fR structure.
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.PP
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When a hash table entry is replaced, \fIlh_insert()\fR returns the value
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being replaced. \fBNULL\fR is returned on normal operation and on error.
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.PP
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\fIlh_delete()\fR returns the entry being deleted. \fBNULL\fR is returned if
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there is no such value in the hash table.
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.PP
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\fIlh_retrieve()\fR returns the hash table entry if it has been found,
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\fBNULL\fR otherwise.
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.PP
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\fIlh_error()\fR returns 1 if an error occurred in the last operation, 0
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otherwise.
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.PP
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\fIlh_free()\fR, \fIlh_doall()\fR and \fIlh_doall_arg()\fR return no values.
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.SH "BUGS"
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\fIlh_insert()\fR returns \fBNULL\fR both for success and error.
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.SH "INTERNALS"
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The following description is based on the SSLeay documentation:
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.PP
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The \fBlhash\fR library implements a hash table described in the
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\fICommunications of the ACM\fR in 1991. What makes this hash table
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different is that as the table fills, the hash table is increased (or
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decreased) in size via \fIRealloc()\fR. When a \*(L'resize\*(R' is done, instead of
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all hashes being redistributed over twice as many \*(L'buckets\*(R', one
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bucket is split. So when an \*(L'expand\*(R' is done, there is only a minimal
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cost to redistribute some values. Subsequent inserts will cause more
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single \*(L'bucket\*(R' redistributions but there will never be a sudden large
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cost due to redistributing all the \*(L'buckets\*(R'.
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.PP
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The state for a particular hash table is kept in the \fBLHASH\fR structure.
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The decision to increase or decrease the hash table size is made
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depending on the \*(L'load\*(R' of the hash table. The load is the number of
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items in the hash table divided by the size of the hash table. The
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default values are as follows. If (hash->up_load < load) =>
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expand. if (hash->down_load > load) => contract. The
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\fBup_load\fR has a default value of 1 and \fBdown_load\fR has a default value
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of 2. These numbers can be modified by the application by just
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playing with the \fBup_load\fR and \fBdown_load\fR variables. The \*(L'load\*(R' is
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kept in a form which is multiplied by 256. So
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hash->up_load=8*256; will cause a load of 8 to be set.
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.PP
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If you are interested in performance the field to watch is
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num_comp_calls. The hash library keeps track of the \*(L'hash\*(R' value for
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each item so when a lookup is done, the \*(L'hashes\*(R' are compared, if
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there is a match, then a full compare is done, and
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hash->num_comp_calls is incremented. If num_comp_calls is not equal
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to num_delete plus num_retrieve it means that your hash function is
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generating hashes that are the same for different values. It is
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probably worth changing your hash function if this is the case because
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even if your hash table has 10 items in a \*(L'bucket\*(R', it can be searched
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with 10 \fBunsigned long\fR compares and 10 linked list traverses. This
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will be much less expensive that 10 calls to you compare function.
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.PP
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\fIlh_strhash()\fR is a demo string hashing function:
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.PP
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.Vb 1
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\& unsigned long lh_strhash(const char *c);
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.Ve
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Since the \fBLHASH\fR routines would normally be passed structures, this
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routine would not normally be passed to \fIlh_new()\fR, rather it would be
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used in the function passed to \fIlh_new()\fR.
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.SH "SEE ALSO"
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the \fIlh_stats(3)|lh_stats(3)\fR manpage
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.SH "HISTORY"
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The \fBlhash\fR library is available in all versions of SSLeay and OpenSSL.
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\fIlh_error()\fR was added in SSLeay 0.9.1b.
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.PP
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This manpage is derived from the SSLeay documentation.
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.rn }` ''
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.IX Title "lhash 3"
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.IX Name "lh_new, lh_free, lh_insert, lh_delete, lh_retrieve, lh_doall,
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lh_doall_arg, lh_error - dynamic hash table"
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.IX Header "NAME"
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.IX Header "SYNOPSIS"
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.IX Header "DESCRIPTION"
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.IX Header "RETURN VALUES"
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.IX Header "BUGS"
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.IX Header "INTERNALS"
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.IX Header "SEE ALSO"
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.IX Header "HISTORY"
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