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package VarnishMib::HashTable;
use strict;
use warnings;
use Carp;
use Inline 'C';
use Pod::Usage;
use Pod::Man;

=head1 NAME

VarnishMib::HashTable - Create a hash table implementation in C

=head1 DESCRIPTION

Given a list of unique strings, creates a C code for fast look ups of
data associated with them.

=head1 CONSTRUCTOR

    $ht = new VarnishMib::HashTable([KW => VAL,...]);

Returns a new instance of the hash table generator. Allowed arguments are:

=over 4

=item B<max_collisions>

Maximum number of collisions allowed for the resulting hash table. Default is
unlimited.    

=item B<max_hash_size>

Maximum size of the resulting hash table (in items).

=item B<indent>

Basic indent value for the generated C text. Default is 4.
    
=item B<verbose>

Produce verbose statistics about the created hash table.

=item B<prefix>

Prefix all C identifiers with this string. Default is C<ht_>.

=back    
    
=cut    

sub new {
    my $class = shift;
    my $self = bless {}, $class;
    my $v;
    local %_ = @_;
    $self->{max_collisions} = delete $_{max_collisions};
    $self->{max_hash_size} = delete $_{max_hash_size};
    $self->{indent} = ' ' x (delete $_{indent} || 4);
    $self->{verbose} = delete $_{verbose};
    $self->{prefix} = delete $_{prefix} || 'ht_';
    croak "extra arguments" if keys %_;
    return $self;
}

=head1 METHODS

=head2 prefix

    $s = $ht->prefix;

Returns current prefix value.

=cut    

sub prefix { shift->{prefix} }

=head2 indent

    $s = $ht->indent;

Returns the indent prefix string. I<Note>, that it is not the same as the
B<ident> parameter passed to the constructor. This method returs a string
filled with appropriate number of whitespace characters, such that it can
be used to produce the requested indentation.    

=cut

sub indent { shift->{indent} }

sub hash_string {
    my ($self, $string, $hash_size) = @_;
    string_hash($string, $hash_size);
}

sub _mktab {
    my ($self, $hash_size) = @_;
    my @ht = (-1) x $hash_size;
    my $cmax = 0;
    for (my $i = 0; $i < @{$self->{input}}; $i++) {
	my $h = $self->hash_string($self->{input}[$i], $hash_size);
	my $cn = 0;
	while ($ht[$h] != -1) {
	    ++$cn;
	    return if (++$h >= $hash_size);
	}
	$ht[$h] = $i;
#	print STDERR $self->{input}[$i] . ' => ' . $h ." $i\n";
	$cmax = $cn if $cn > $cmax;
    }
#    print STDERR "$hash_size $cmax\n";
    $self->{hash_table} = \@ht;
    $self->{collisions} = $cmax;
    return $self->{hash_table};
}

=head2 create

    $success = $ht->create(LISTREF)

B<LISTREF> must be a reference to a list of unique string values. This method
creates a hash table. Returns true on success and undef on failure.

=cut
    
sub create {
    my ($self, $names) = @_;
    my $htab;
    my $hsize;

    $self->{input} = $names;
    delete $self->{hash_table};

    for ($hsize = (2 * @$names + 1);; $hsize++) {
	last if $self->{max_hash_size} && $hsize < $self->{max_hash_size};
	$self->_mktab($hsize) or next;
	last unless (defined($self->{max_collisions})
		     && $self->{collisions} > $self->{max_collisions});
    }
    if ($self->{verbose}) {
#	print STDERR "Input: " . @$names . "\n";
	if ($self->{hash_table}) {
	    print STDERR "Table size: " . @{$self->{hash_table}} . "\n";
	    print STDERR "Collisions: " . $self->{collisions} . "\n";
	} else {
	    print STDERR "FAILED\n";
	}
    }
    return $self->{hash_table};
}

=head2 format_input_table

    $ht->format_input_table([FILEHANDLE]);

Outputs to I<FILEHANDLE> (default B<STDOUT>) a C array of input names. The
array is declared as

    char const *PFXname_table[]

where I<PFX> is replaced by the prefix given when creating the HashTable
object.    

=cut

sub format_input_table {
    my ($self, $fh) = @_;
    $fh ||= \*STDOUT;
    croak "no input data to format" unless $self->{input};
    print $fh 'static char const *' . $self->{prefix} . "name_table[] = {\n";    
    foreach my $name (@{$self->{input}}) {
	printf $fh $self->{indent} . '"' . $name . "\",\n";
    }
    print $fh "};\n";
    
}

=head2 format_data_table

    $ht->format_data_table(CTYPE [, FILEHANDLE])

Outputs a C array of data associated with input strings. The array is declared
as

    CTYPE PFXdata_table[N];

where I<CTYPE> is the first parameter to the method, I<PFX> is the prefix and
I<N> is the dimension (number of strings for which the hash table is built).
Both B<name_table> and B<data_table> have the same dimension.    

=cut
    
sub format_data_table {
    my ($self, $type, $fh) = @_;
    $fh ||= \*STDOUT;
    croak "no data to format" unless $self->{input};
    my $n = @{$self->{input}};
    print $fh 'static '. $type . ' ' . $self->{prefix} . "data_table[$n];\n";
}

=head2 format_hash_table

    $ht->format_hash_table([FILEHANDLE]);


Outputs the hash table to I<FILEHANDLE> (B<STDOUT> by default). The table
is declared as    

    int PFXhash_table[]

where I<PFX> is the prefix.
    
=cut

sub format_hash_table {
    my ($self, $fh) = @_;
    $fh ||= \*STDOUT;
    croak "no hash table to format" unless $self->{hash_table};
    print $fh "static int ".$self->{prefix}."hash_table[] = {\n";
    my $col = 0;
    print $fh $self->{indent};
    foreach my $p (@{$self->{hash_table}}) {
	printf $fh "%3d,", defined($p) ? $p : -1;
	$col++;
	print $fh ($col % 10 == 0) ? "\n".$self->{indent} : ' ';
    }
    print $fh "\n" if ($col % 10);
    print $fh "};\n";
    my $pfx = $self->{prefix} . 'hash_table';
    print $fh "unsigned ${pfx}_size = sizeof($pfx) / sizeof(${pfx}[0]);\n";
}

=head2 format_code

    $ht->format_code([FILEHANDLE])

Formats the supporting C code to the I<FILEHANDLE> (B<STDOUT>, if not given).
The code contains at least the following function:
    
    unsigned string_hash(const char *str, unsigned size)

which, given the string I<str> and the size of the hash table (I<size>)
returns the index in the table starting from which the pointer to that
string and associated data can be located.
    
=cut

sub format_code {
    my ($self, $fh) = @_;
    $fh ||= \*STDOUT;
    seek DATA, 0, 0;
    my $visible = 0;
    while (<DATA>) {
	if (/^__C__$/) {
	    $visible = 1;
	} elsif ($visible) {
	    s{/\*\s*STATIC\s*\*/}{static};
	    print $fh "$_";
	}
    }
}

sub format_program {
    my ($self, $type, $fh) = @_;
    $fh ||= \*STDOUT;
    $self->format_input_table($fh);
    print $fh "\n";
    $self->format_data_table($type, $fh);
    print $fh "\n";
    $self->format_hash_table($fh);
    print $fh "\n";
    $self->format_code($fh);
}

Inline->init();
1;
__DATA__
__C__
#ifndef CHAR_BIT
# define CHAR_BIT 8
#endif
#ifndef UINT_MAX
# define UINT_MAX ((unsigned)-1)
#endif
    
static inline unsigned
rotl_sz(unsigned x, int n)
{
    return ((x << n) | (x >> ((CHAR_BIT * sizeof x) - n))) & UINT_MAX;
}

/*STATIC*/ unsigned
string_hash(const char *str, unsigned size)
{
    unsigned value = 0;
    unsigned char ch;

    for (; (ch = *str); str++)
	value = ch + rotl_sz(value, 7);
    return value % size;
}

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