documentation patch for 5.004_57

[p5sagit/p5-mst-13.2.git] / lib / Tie / SubstrHash.pm

diff --git a/lib/Tie/SubstrHash.pm b/lib/Tie/SubstrHash.pm
index 6250e73..44c2140 100644 (file)
--- a/lib/Tie/SubstrHash.pm
+++ b/lib/Tie/SubstrHash.pm
@@ -1,4 +1,40 @@
-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 {
@@ -108,13 +144,17 @@ sub hashkey {
     $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;