1*0Sstevel@tonic-gatepackage Tie::SubstrHash; 2*0Sstevel@tonic-gate 3*0Sstevel@tonic-gateour $VERSION = '1.00'; 4*0Sstevel@tonic-gate 5*0Sstevel@tonic-gate=head1 NAME 6*0Sstevel@tonic-gate 7*0Sstevel@tonic-gateTie::SubstrHash - Fixed-table-size, fixed-key-length hashing 8*0Sstevel@tonic-gate 9*0Sstevel@tonic-gate=head1 SYNOPSIS 10*0Sstevel@tonic-gate 11*0Sstevel@tonic-gate require Tie::SubstrHash; 12*0Sstevel@tonic-gate 13*0Sstevel@tonic-gate tie %myhash, 'Tie::SubstrHash', $key_len, $value_len, $table_size; 14*0Sstevel@tonic-gate 15*0Sstevel@tonic-gate=head1 DESCRIPTION 16*0Sstevel@tonic-gate 17*0Sstevel@tonic-gateThe B<Tie::SubstrHash> package provides a hash-table-like interface to 18*0Sstevel@tonic-gatean array of determinate size, with constant key size and record size. 19*0Sstevel@tonic-gate 20*0Sstevel@tonic-gateUpon tying a new hash to this package, the developer must specify the 21*0Sstevel@tonic-gatesize of the keys that will be used, the size of the value fields that the 22*0Sstevel@tonic-gatekeys will index, and the size of the overall table (in terms of key-value 23*0Sstevel@tonic-gatepairs, not size in hard memory). I<These values will not change for the 24*0Sstevel@tonic-gateduration of the tied hash>. The newly-allocated hash table may now have 25*0Sstevel@tonic-gatedata stored and retrieved. Efforts to store more than C<$table_size> 26*0Sstevel@tonic-gateelements will result in a fatal error, as will efforts to store a value 27*0Sstevel@tonic-gatenot exactly C<$value_len> characters in length, or reference through a 28*0Sstevel@tonic-gatekey not exactly C<$key_len> characters in length. While these constraints 29*0Sstevel@tonic-gatemay seem excessive, the result is a hash table using much less internal 30*0Sstevel@tonic-gatememory than an equivalent freely-allocated hash table. 31*0Sstevel@tonic-gate 32*0Sstevel@tonic-gate=head1 CAVEATS 33*0Sstevel@tonic-gate 34*0Sstevel@tonic-gateBecause the current implementation uses the table and key sizes for the 35*0Sstevel@tonic-gatehashing algorithm, there is no means by which to dynamically change the 36*0Sstevel@tonic-gatevalue of any of the initialization parameters. 37*0Sstevel@tonic-gate 38*0Sstevel@tonic-gateThe hash does not support exists(). 39*0Sstevel@tonic-gate 40*0Sstevel@tonic-gate=cut 41*0Sstevel@tonic-gate 42*0Sstevel@tonic-gateuse Carp; 43*0Sstevel@tonic-gate 44*0Sstevel@tonic-gatesub TIEHASH { 45*0Sstevel@tonic-gate my $pack = shift; 46*0Sstevel@tonic-gate my ($klen, $vlen, $tsize) = @_; 47*0Sstevel@tonic-gate my $rlen = 1 + $klen + $vlen; 48*0Sstevel@tonic-gate $tsize = [$tsize, 49*0Sstevel@tonic-gate findgteprime($tsize * 1.1)]; # Allow 10% empty. 50*0Sstevel@tonic-gate local $self = bless ["\0", $klen, $vlen, $tsize, $rlen, 0, -1]; 51*0Sstevel@tonic-gate $$self[0] x= $rlen * $tsize->[1]; 52*0Sstevel@tonic-gate $self; 53*0Sstevel@tonic-gate} 54*0Sstevel@tonic-gate 55*0Sstevel@tonic-gatesub CLEAR { 56*0Sstevel@tonic-gate local($self) = @_; 57*0Sstevel@tonic-gate $$self[0] = "\0" x ($$self[4] * $$self[3]->[1]); 58*0Sstevel@tonic-gate $$self[5] = 0; 59*0Sstevel@tonic-gate $$self[6] = -1; 60*0Sstevel@tonic-gate} 61*0Sstevel@tonic-gate 62*0Sstevel@tonic-gatesub FETCH { 63*0Sstevel@tonic-gate local($self,$key) = @_; 64*0Sstevel@tonic-gate local($klen, $vlen, $tsize, $rlen) = @$self[1..4]; 65*0Sstevel@tonic-gate &hashkey; 66*0Sstevel@tonic-gate for (;;) { 67*0Sstevel@tonic-gate $offset = $hash * $rlen; 68*0Sstevel@tonic-gate $record = substr($$self[0], $offset, $rlen); 69*0Sstevel@tonic-gate if (ord($record) == 0) { 70*0Sstevel@tonic-gate return undef; 71*0Sstevel@tonic-gate } 72*0Sstevel@tonic-gate elsif (ord($record) == 1) { 73*0Sstevel@tonic-gate } 74*0Sstevel@tonic-gate elsif (substr($record, 1, $klen) eq $key) { 75*0Sstevel@tonic-gate return substr($record, 1+$klen, $vlen); 76*0Sstevel@tonic-gate } 77*0Sstevel@tonic-gate &rehash; 78*0Sstevel@tonic-gate } 79*0Sstevel@tonic-gate} 80*0Sstevel@tonic-gate 81*0Sstevel@tonic-gatesub STORE { 82*0Sstevel@tonic-gate local($self,$key,$val) = @_; 83*0Sstevel@tonic-gate local($klen, $vlen, $tsize, $rlen) = @$self[1..4]; 84*0Sstevel@tonic-gate croak("Table is full ($tsize->[0] elements)") if $$self[5] > $tsize->[0]; 85*0Sstevel@tonic-gate croak(qq/Value "$val" is not $vlen characters long/) 86*0Sstevel@tonic-gate if length($val) != $vlen; 87*0Sstevel@tonic-gate my $writeoffset; 88*0Sstevel@tonic-gate 89*0Sstevel@tonic-gate &hashkey; 90*0Sstevel@tonic-gate for (;;) { 91*0Sstevel@tonic-gate $offset = $hash * $rlen; 92*0Sstevel@tonic-gate $record = substr($$self[0], $offset, $rlen); 93*0Sstevel@tonic-gate if (ord($record) == 0) { 94*0Sstevel@tonic-gate $record = "\2". $key . $val; 95*0Sstevel@tonic-gate die "panic" unless length($record) == $rlen; 96*0Sstevel@tonic-gate $writeoffset = $offset unless defined $writeoffset; 97*0Sstevel@tonic-gate substr($$self[0], $writeoffset, $rlen) = $record; 98*0Sstevel@tonic-gate ++$$self[5]; 99*0Sstevel@tonic-gate return; 100*0Sstevel@tonic-gate } 101*0Sstevel@tonic-gate elsif (ord($record) == 1) { 102*0Sstevel@tonic-gate $writeoffset = $offset unless defined $writeoffset; 103*0Sstevel@tonic-gate } 104*0Sstevel@tonic-gate elsif (substr($record, 1, $klen) eq $key) { 105*0Sstevel@tonic-gate $record = "\2". $key . $val; 106*0Sstevel@tonic-gate die "panic" unless length($record) == $rlen; 107*0Sstevel@tonic-gate substr($$self[0], $offset, $rlen) = $record; 108*0Sstevel@tonic-gate return; 109*0Sstevel@tonic-gate } 110*0Sstevel@tonic-gate &rehash; 111*0Sstevel@tonic-gate } 112*0Sstevel@tonic-gate} 113*0Sstevel@tonic-gate 114*0Sstevel@tonic-gatesub DELETE { 115*0Sstevel@tonic-gate local($self,$key) = @_; 116*0Sstevel@tonic-gate local($klen, $vlen, $tsize, $rlen) = @$self[1..4]; 117*0Sstevel@tonic-gate &hashkey; 118*0Sstevel@tonic-gate for (;;) { 119*0Sstevel@tonic-gate $offset = $hash * $rlen; 120*0Sstevel@tonic-gate $record = substr($$self[0], $offset, $rlen); 121*0Sstevel@tonic-gate if (ord($record) == 0) { 122*0Sstevel@tonic-gate return undef; 123*0Sstevel@tonic-gate } 124*0Sstevel@tonic-gate elsif (ord($record) == 1) { 125*0Sstevel@tonic-gate } 126*0Sstevel@tonic-gate elsif (substr($record, 1, $klen) eq $key) { 127*0Sstevel@tonic-gate substr($$self[0], $offset, 1) = "\1"; 128*0Sstevel@tonic-gate return substr($record, 1+$klen, $vlen); 129*0Sstevel@tonic-gate --$$self[5]; 130*0Sstevel@tonic-gate } 131*0Sstevel@tonic-gate &rehash; 132*0Sstevel@tonic-gate } 133*0Sstevel@tonic-gate} 134*0Sstevel@tonic-gate 135*0Sstevel@tonic-gatesub FIRSTKEY { 136*0Sstevel@tonic-gate local($self) = @_; 137*0Sstevel@tonic-gate $$self[6] = -1; 138*0Sstevel@tonic-gate &NEXTKEY; 139*0Sstevel@tonic-gate} 140*0Sstevel@tonic-gate 141*0Sstevel@tonic-gatesub NEXTKEY { 142*0Sstevel@tonic-gate local($self) = @_; 143*0Sstevel@tonic-gate local($klen, $vlen, $tsize, $rlen, $entries, $iterix) = @$self[1..6]; 144*0Sstevel@tonic-gate for (++$iterix; $iterix < $tsize->[1]; ++$iterix) { 145*0Sstevel@tonic-gate next unless substr($$self[0], $iterix * $rlen, 1) eq "\2"; 146*0Sstevel@tonic-gate $$self[6] = $iterix; 147*0Sstevel@tonic-gate return substr($$self[0], $iterix * $rlen + 1, $klen); 148*0Sstevel@tonic-gate } 149*0Sstevel@tonic-gate $$self[6] = -1; 150*0Sstevel@tonic-gate undef; 151*0Sstevel@tonic-gate} 152*0Sstevel@tonic-gate 153*0Sstevel@tonic-gatesub EXISTS { 154*0Sstevel@tonic-gate croak "Tie::SubstrHash does not support exists()"; 155*0Sstevel@tonic-gate} 156*0Sstevel@tonic-gate 157*0Sstevel@tonic-gatesub hashkey { 158*0Sstevel@tonic-gate croak(qq/Key "$key" is not $klen characters long/) 159*0Sstevel@tonic-gate if length($key) != $klen; 160*0Sstevel@tonic-gate $hash = 2; 161*0Sstevel@tonic-gate for (unpack('C*', $key)) { 162*0Sstevel@tonic-gate $hash = $hash * 33 + $_; 163*0Sstevel@tonic-gate &_hashwrap if $hash >= 1e13; 164*0Sstevel@tonic-gate } 165*0Sstevel@tonic-gate &_hashwrap if $hash >= $tsize->[1]; 166*0Sstevel@tonic-gate $hash = 1 unless $hash; 167*0Sstevel@tonic-gate $hashbase = $hash; 168*0Sstevel@tonic-gate} 169*0Sstevel@tonic-gate 170*0Sstevel@tonic-gatesub _hashwrap { 171*0Sstevel@tonic-gate $hash -= int($hash / $tsize->[1]) * $tsize->[1]; 172*0Sstevel@tonic-gate} 173*0Sstevel@tonic-gate 174*0Sstevel@tonic-gatesub rehash { 175*0Sstevel@tonic-gate $hash += $hashbase; 176*0Sstevel@tonic-gate $hash -= $tsize->[1] if $hash >= $tsize->[1]; 177*0Sstevel@tonic-gate} 178*0Sstevel@tonic-gate 179*0Sstevel@tonic-gate# using POSIX::ceil() would be too heavy, and not all platforms have it. 180*0Sstevel@tonic-gatesub ceil { 181*0Sstevel@tonic-gate my $num = shift; 182*0Sstevel@tonic-gate $num = int($num + 1) unless $num == int $num; 183*0Sstevel@tonic-gate return $num; 184*0Sstevel@tonic-gate} 185*0Sstevel@tonic-gate 186*0Sstevel@tonic-gate# See: 187*0Sstevel@tonic-gate# 188*0Sstevel@tonic-gate# http://www-groups.dcs.st-andrews.ac.uk/~history/HistTopics/Prime_numbers.html 189*0Sstevel@tonic-gate# 190*0Sstevel@tonic-gate 191*0Sstevel@tonic-gatesub findgteprime { # find the smallest prime integer greater than or equal to 192*0Sstevel@tonic-gate use integer; 193*0Sstevel@tonic-gate 194*0Sstevel@tonic-gate my $num = ceil(shift); 195*0Sstevel@tonic-gate return 2 if $num <= 2; 196*0Sstevel@tonic-gate 197*0Sstevel@tonic-gate $num++ unless $num % 2; 198*0Sstevel@tonic-gate my $i; 199*0Sstevel@tonic-gate my $sqrtnum = int sqrt $num; 200*0Sstevel@tonic-gate my $sqrtnumsquared = $sqrtnum * $sqrtnum; 201*0Sstevel@tonic-gate 202*0Sstevel@tonic-gate NUM: 203*0Sstevel@tonic-gate for (;; $num += 2) { 204*0Sstevel@tonic-gate if ($sqrtnumsquared < $num) { 205*0Sstevel@tonic-gate $sqrtnum++; 206*0Sstevel@tonic-gate $sqrtnumsquared = $sqrtnum * $sqrtnum; 207*0Sstevel@tonic-gate } 208*0Sstevel@tonic-gate for ($i = 3; $i <= $sqrtnum; $i += 2) { 209*0Sstevel@tonic-gate next NUM unless $num % $i; 210*0Sstevel@tonic-gate } 211*0Sstevel@tonic-gate return $num; 212*0Sstevel@tonic-gate } 213*0Sstevel@tonic-gate} 214*0Sstevel@tonic-gate 215*0Sstevel@tonic-gate1; 216