-package SubstrHash;
+package Tie::SubstrHash;
+
+=head1 NAME
+
+Tie::SubstrHash - Fixed-table-size, fixed-key-length hashing
+
+=head1 SYNOPSIS
+
+ require Tie::SubstrHash;
+
+ tie %myhash, 'Tie::SubstrHash', $key_len, $value_len, $table_size;
+
+=head1 DESCRIPTION
+
+The B<Tie::SubstrHash> package provides a hash-table-like interface to
+an array of determinate size, with constant key size and record size.
+
+Upon tying a new hash to this package, the developer must specify the
+size of the keys that will be used, the size of the value fields that the
+keys will index, and the size of the overall table (in terms of key-value
+pairs, not size in hard memory). I<These values will not change for the
+duration of the tied hash>. The newly-allocated hash table may now have
+data stored and retrieved. Efforts to store more than C<$table_size>
+elements will result in a fatal error, as will efforts to store a value
+not exactly C<$value_len> characters in length, or reference through a
+key not exactly C<$key_len> characters in length. While these constraints
+may seem excessive, the result is a hash table using much less internal
+memory than an equivalent freely-allocated hash table.
+
+=head1 CAVEATS
+
+Because the current implementation uses the table and key sizes for the
+hashing algorithm, there is no means by which to dynamically change the
+value of any of the initialization parameters.
+
+=cut
+
use Carp;
sub TIEHASH {
sub STORE {
local($self,$key,$val) = @_;
local($klen, $vlen, $tsize, $rlen) = @$self[1..4];
- croak("Table is full") if $self[5] == $tsize;
+ croak("Table is full") if $$self[5] == $tsize;
croak(qq/Value "$val" is not $vlen characters long./)
if length($val) != $vlen;
my $writeoffset;
$hash = 2;
for (unpack('C*', $key)) {
$hash = $hash * 33 + $_;
+ &_hashwrap if $hash >= 1e13;
}
- $hash = $hash - int($hash / $tsize) * $tsize
- if $hash >= $tsize;
+ &_hashwrap if $hash >= $tsize;
$hash = 1 unless $hash;
$hashbase = $hash;
}
+sub _hashwrap {
+ $hash -= int($hash / $tsize) * $tsize;
+}
+
sub rehash {
$hash += $hashbase;
$hash -= $tsize if $hash >= $tsize;