The Annoyance Filter.pdf - Fourmilab

§35 ANNOYANCE-FILTER FAST DICTIONARY 39
35. The exportDictionary method writes a dictionary to a file in fastDictionary format. We provide
implementations which accept either an ostream of the name of a file to which the fastDictionary
is written. If you pass an ostream, make sure it’s opened in binary mode on platforms where that
matters.
〈 Class implementations 11 〉 +≡
void fastDictionary ::exportDictionary (const dictionary &d, ostream &o)
{
u int32 t hashSize = nextGreaterPrime (d.size ( ));
vector〈u int32 t 〉 hashTable (hashSize , fastDictionaryVoidLink );
vector〈unsigned char〉 words ;
for (dictionary ::const iterator w = d.begin ( ); w ≠ d.end ( ); w++) {
u int32 t h = computeHashValue (w ⃗ first );
unsigned int slot = h % hashSize ;
〈 Link new word to hash table chain 36 〉;
〈 Add new word to word table 37 〉;
}
o ≪ fastDictionarySignature ;
u int16 t b;
b = byteOrderMark ;
o.write (reinterpret cast〈const char ∗〉(&b), sizeof b); /∗ Byte order mark ∗/
b = versionNumber ;
o.write (reinterpret cast〈const char ∗〉(&b), sizeof b); /∗ File version number ∗/
b = doubleSize ;
o.write (reinterpret cast〈const char ∗〉(&b), sizeof b); /∗ Size of double in bytes ∗/
b = 0;
o.write (reinterpret cast〈const char ∗〉(&b), sizeof b); /∗ 88 Filler size is 2 bytes ∗/
double td = fastDictionaryFloatingTest ;
o.write (reinterpret cast〈const char ∗〉(&td ), sizeof td );
1
/∗ double compatibility test:
111 ∗/
u int32 t headerSize = 4 + (4 ∗ sizeof (u int16 t )) + sizeof (double) + (4 ∗ sizeof (u int32 t ));
u int32 t wordTableSize = words .size ( );
u int32 t totalSize = headerSize + (hashTable .size ( ) ∗ sizeof (u int32 t )) + wordTableSize ;
o.write (reinterpret cast〈const char ∗〉(&totalSize ), sizeof totalSize );
/∗ Total size of file ∗/
o.write (reinterpret cast〈const char ∗〉(&headerSize ), sizeof headerSize );
/∗ Hash table offset ∗/
o.write (reinterpret cast〈const char ∗〉(&hashSize ), sizeof hashSize );
/∗ Number of buckets in hash table ∗/
o.write (reinterpret cast〈const char ∗〉(&wordTableSize ), sizeof wordTableSize );
/∗ Word table size in bytes ∗/
#ifdef OLDWAY
o.write (hashTable .begin ( ), hashTable .size ( ) ∗ sizeof (u int32 t )); /∗ Hash table ∗/
o.write (words .begin ( ), words .size ( )); /∗ Word table ∗/
#else
for (vector〈u int32 t 〉::const iterator htp = hashTable .begin ( ); htp ≠ hashTable .end ( ); htp ++) {
u int32 t hte = ∗htp;
o.write (reinterpret cast〈const char ∗〉(&hte ), sizeof hte );
}
for (vector〈unsigned char〉::const iterator wtp = words .begin ( ); wtp ≠ words .end ( ); wtp ++) {
o.put (∗wtp);