1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
|
# -*- perl -*-
#
# Perfect Minimal Hash Generator written in Perl, which produces
# C output.
#
# Requires the CPAN Graph module (tested against 0.81, 0.83, 0.84)
#
require 'random_sv_vectors.ph';
require 'crc64.ph';
#
# Compute the prehash for a key
#
# prehash(key, sv, N)
#
sub prehash($$$) {
my($key, $n, $sv) = @_;
my @c = crc64($sv, $key);
# Create a bipartite graph...
$k1 = (($c[1] & ($n-1)) << 1) + 0; # low word
$k2 = (($c[0] & ($n-1)) << 1) + 1; # high word
return ($k1, $k2);
}
#
# Walk the assignment graph, return true on success
#
sub walk_graph($$$$) {
my($nodeval,$nodeneigh,$n,$v) = @_;
my $nx;
# print STDERR "Vertex $n value $v\n";
$$nodeval[$n] = $v;
foreach $nx (@{$$nodeneigh[$n]}) {
# $nx -> [neigh, hash]
my ($o, $e) = @$nx;
# print STDERR "Edge $n,$o value $e: ";
my $ov;
if (defined($ov = $$nodeval[$o])) {
if ($v+$ov != $e) {
# Cyclic graph with collision
# print STDERR "error, should be ", $v+$ov, "\n";
return 0;
} else {
# print STDERR "ok\n";
}
} else {
return 0 unless (walk_graph($nodeval, $nodeneigh, $o, $e-$v));
}
}
return 1;
}
#
# Generate the function assuming a given N.
#
# gen_hash_n(N, sv, \%data, run)
#
sub gen_hash_n($$$$) {
my($n, $sv, $href, $run) = @_;
my @keys = keys(%{$href});
my $i, $sv;
my $gr;
my $k, $v;
my $gsize = 2*$n;
my @nodeval;
my @nodeneigh;
my %edges;
for ($i = 0; $i < $gsize; $i++) {
$nodeneigh[$i] = [];
}
%edges = ();
foreach $k (@keys) {
my ($pf1, $pf2) = prehash($k, $n, $sv);
($pf1,$pf2) = ($pf2,$pf1) if ($pf1 > $pf2); # Canonicalize order
my $pf = "$pf1,$pf2";
my $e = ${$href}{$k};
my $xkey;
if (defined($xkey = $edges{$pf})) {
next if ($e == ${$href}{$xkey}); # Duplicate hash, safe to ignore
if (defined($run)) {
print STDERR "$run: Collision: $pf: $k with $xkey\n";
}
return;
}
# print STDERR "Edge $pf value $e from $k\n";
$edges{$pf} = $k;
push(@{$nodeneigh[$pf1]}, [$pf2, $e]);
push(@{$nodeneigh[$pf2]}, [$pf1, $e]);
}
# Now we need to assign values to each vertex, so that for each
# edge, the sum of the values for the two vertices give the value
# for the edge (which is our hash index.) If we find an impossible
# sitation, the graph was cyclic.
@nodeval = (undef) x $gsize;
for ($i = 0; $i < $gsize; $i++) {
if (scalar(@{$nodeneigh[$i]})) {
# This vertex has neighbors (is used)
if (!defined($nodeval[$i])) {
# First vertex in a cluster
unless (walk_graph(\@nodeval, \@nodeneigh, $i, 0)) {
if (defined($run)) {
print STDERR "$run: Graph is cyclic\n";
}
return;
}
}
}
}
# for ($i = 0; $i < $n; $i++) {
# print STDERR "Vertex ", $i, ": ", $g[$i], "\n";
# }
if (defined($run)) {
printf STDERR "$run: Done: n = $n, sv = [0x%08x, 0x%08x]\n",
$$sv[0], $$sv[1];
}
return ($n, $sv, \@nodeval);
}
#
# Driver for generating the function
#
# gen_perfect_hash(\%data)
#
sub gen_perfect_hash($) {
my($href) = @_;
my @keys = keys(%{$href});
my @hashinfo;
my $n, $i, $j, $sv, $maxj;
my $run = 1;
# Minimal power of 2 value for N with enough wiggle room.
# The scaling constant must be larger than 0.5 in order for the
# algorithm to ever terminate.
my $room = scalar(@keys)*0.8;
$n = 1;
while ($n < $room) {
$n <<= 1;
}
# Number of times to try...
$maxj = scalar @random_sv_vectors;
for ($i = 0; $i < 4; $i++) {
printf STDERR "%d vectors, trying n = %d...\n",
scalar @keys, $n;
for ($j = 0; $j < $maxj; $j++) {
$sv = $random_sv_vectors[$j];
@hashinfo = gen_hash_n($n, $sv, $href, $run++);
return @hashinfo if (defined(@hashinfo));
}
$n <<= 1;
}
return;
}
#
# Read input file
#
sub read_input() {
my $key,$val;
my %out;
my $x = 0;
while (defined($l = <STDIN>)) {
chomp $l;
$l =~ s/\s*(\#.*|)$//;
next if ($l eq '');
if ($l =~ /^([^=]+)\=([^=]+)$/) {
$out{$1} = $2;
$x = $2;
} else {
$out{$l} = $x;
}
$x++;
}
return %out;
}
#
# Verify that the hash table is actually correct...
#
sub verify_hash_table($$)
{
my ($href, $hashinfo) = @_;
my ($n, $sv, $g) = @{$hashinfo};
my $k;
my $err = 0;
foreach $k (keys(%$href)) {
my ($pf1, $pf2) = prehash($k, $n, $sv);
my $g1 = ${$g}[$pf1];
my $g2 = ${$g}[$pf2];
if ($g1+$g2 != ${$href}{$k}) {
printf STDERR "%s(%d,%d): %d+%d = %d != %d\n",
$k, $pf1, $pf2, $g1, $g2, $g1+$g2, ${$href}{$k};
$err = 1;
} else {
# printf STDERR "%s: %d+%d = %d ok\n",
# $k, $g1, $g2, $g1+$g2;
}
}
die "$0: hash validation error\n" if ($err);
}
1;
|
