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/**
* Copyright (C) 2010-2018 Gordon Fraser, Andrea Arcuri and EvoSuite
* contributors
*
* This file is part of EvoSuite.
*
* EvoSuite is free software: you can redistribute it and/or modify it
* under the terms of the GNU Lesser General Public License as published
* by the Free Software Foundation, either version 3.0 of the License, or
* (at your option) any later version.
*
* EvoSuite is distributed in the hope that it will be useful, but
* WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
* Lesser Public License for more details.
*
* You should have received a copy of the GNU Lesser General Public
* License along with EvoSuite. If not, see .
*/
package org.evosuite.lm;
import java.io.*;
import java.util.HashMap;
import java.util.Map;
import java.util.TreeMap;
import java.util.Comparator;
import java.util.regex.Pattern;
import java.util.regex.Matcher;
/**
* Represents a language model, a set of bigrams, unigrams and associated
* log-probabilities.
*/
public class LangModel {
// class variables
// Hashes storing various Language Model probabilities
/**
* Probability of a unigram occurring.
*/
private Map unigram_probs = new HashMap();
/**
* Unigram backoff probabilities (used in bigram probability estimation).
*/
private Map unigram_backoff_probs = new HashMap();
/**
* Probability that Unigram2 follows Unigram1, where each key is of the form "Unigram1 Unigram2".
*/
private Map bigram_probs = new HashMap();
//Sentinel unigram values:
public static final String START_OF_STRING = "";
public static final String END_OF_STRING="";
public static final String START_NEW_WORD="";
private double unknown_char_prob = 0;
// Hashes to store most probable next characters in bigram
/**
* Mapping of the nth most likely unigrams to follow each unigram.
* Encoded as: (unigram)(n)> -> (unigram)
*/
private HashMap context_char = new HashMap();
/**
* Mapping of the probability of the nth most likely unigram to follow each unigram.
* Encoded as: (unigram)(n)> -> (log_probability)
*/
private HashMap context_prob = new HashMap();
// Maximum number of characters to predict for each bigram
int predicted_chars = 10;
// Constructors
// Read in data from language model to be manipulated later
// Takes language model file as argument
/**
* Load the language model.
* @param lmFileName path to a language model file.
* @throws IOException if the model file can't be found or read.
*/
public LangModel(String lmFileName) throws IOException {
// Flag to indicate length of n-grams currently being read (0 == read
// nothing)
int ngram_len = 0; //size of the n-grams we're reading (i.e. ngram_len = 5 implies 5-grams).
InputStream fstream = LangModel.class.getClassLoader().getResourceAsStream(lmFileName);
// FileInputStream fstream = new FileInputStream(lmFileName);
DataInputStream in = new DataInputStream(fstream);
BufferedReader br = new BufferedReader(new InputStreamReader(in));
String strLine;
double highest_unigram_prob = 0;
// Read file line by line
while ((strLine = br.readLine()) != null) {
Pattern ngram_len_p = Pattern.compile("(\\d+)-grams:");
Matcher match_ngram_len = ngram_len_p.matcher(strLine);
//does line match (\d+)-grams: ?
if (match_ngram_len.find()) {
ngram_len = Integer.parseInt(match_ngram_len.group(1));
} else if (ngram_len == 1) {
//We're looking at unigrams;
Pattern unigram_p = Pattern
.compile("([-0-9\\.]+)\\s*(\\S+)\\s*([-0-9\\.]+)");
// Match with
// | | +------ backoff probability
// | +------------------------ unigram
// +-------------------------------------------- unigram probability
Matcher match_unigram = unigram_p.matcher(strLine);
if (match_unigram.find()) {
double unigram_prob = Double.parseDouble(match_unigram
.group(1));
String unigram = match_unigram.group(2);
double unigram_backoff_prob = Double
.parseDouble(match_unigram.group(3));
unigram_probs.put(unigram, unigram_prob);
unigram_backoff_probs.put(unigram, unigram_backoff_prob);
if(unigram_prob < unknown_char_prob) {
unknown_char_prob = unigram_prob;
} // if
if(unigram_prob > highest_unigram_prob) {
highest_unigram_prob = unigram_prob;
} //if
} // if
} else if (ngram_len == 2) {
Pattern bigram_p = Pattern.compile("([-0-9\\.]+)\\s*(\\S+) (\\S+)");
//Match line with
// | | +---- end char of bigram
// | +------------------------- start char of bigram
// +--------------------------------------------- bigram probability
Matcher match_bigram = bigram_p.matcher(strLine);
if (match_bigram.find()) {
double bigram_prob = Double.parseDouble(match_bigram
.group(1));
String bigram_start = match_bigram.group(2);
String bigram_end = match_bigram.group(3);
String bigram = bigram_start + " " + bigram_end;
bigram_probs.put(bigram, bigram_prob);
} // if
} // if/else
} // while
// Close the input stream
in.close();
ValueComparator bvc = new ValueComparator(bigram_probs);
TreeMap sorted_bigram_probs = new TreeMap(
bvc);
//Store bigrams sorted by probability:
sorted_bigram_probs.putAll(bigram_probs);
// Regular expressions setup
Pattern context_p = Pattern.compile("(\\S+) (\\S+)");
//Go through each bigram in order (most likely first) and build a
// table of the predicted_chars most likely characters to follow each character.
for (Map.Entry entry : sorted_bigram_probs.entrySet()) {
Matcher match_context = context_p.matcher(entry.getKey());
if (match_context.find()) {
String pre = match_context.group(1);
String middle = match_context.group(2);
// Add to hash (do this by starting counter at 0 and then
// testing hash and
// filling first empty slot. If no empty slot found then value
// is not stored.
for (int c = 0; c < predicted_chars; c++) {
String key = pre + c;
if (!context_char.containsKey(key)) {
context_char.put(key, middle);
context_prob.put(key, entry.getValue());
break;
} // if
} // for
} // if
} // for
// Print out as sanity check
//for (Map.Entry entry : context_char.entrySet()) {
// System.out.println("Key = " + entry.getKey() + ", Value = " +
// entry.getValue());
//}
} // LangModel
// Method which returns language model score for string str Splits
// string into bigrams and looks up the probability for each. If
// the bigram isn't found then backs off to use the unigram and
// backoff probabilities str is string for which score is
// computed, verbose is flag indicating whether to print out
// details about how this score is computed
/**
* Splits a string into bigrams and calculates the language model score.
* For each bigram, it looks up the probability. The score is the geometric mean
* of the probability of each bigram in the string according to the model.
*
* If a given bigram isn't in the model, unigrams are used to estimate the probability
* of the bigram instead
*
* @param str String for which to compute the score
* @param verbose whether to print information
* @return
*/
public double score(String str, boolean verbose) {
if (verbose == true) {
System.out.println("String is " + str);
} // if
double log_prob = 0;
// Get length of string
int no_chars = str.length();
// Break string down into bigrams
for (int i = -1; i < (no_chars - 1); i++) {
String first_char;
String second_char;
if (i == -1) {
first_char = "";
second_char = str.substring(0, 1);
} else {
first_char = str.substring(i, i + 1);
second_char = str.substring(i + 1, i + 2);
} // if/else
if (first_char.equals(" ")) {
first_char = "";
} // if
if (second_char.equals(" ")) {
second_char = "";
} // if
String bigram = first_char + " " + second_char;
if (verbose == true) {
System.out.println("Bigram is " + bigram);
} // if
// Get negative log likelihood for each bigram
// (Either get directly or estimate using backoff)
if (bigram_probs.containsKey(bigram)) {
// Get direct bigram probabilities
double bigram_prob = bigram_probs.get(bigram);
log_prob = log_prob + bigram_prob;
if (verbose == true) {
System.out.println("Direct bigram prob: "
+ Math.pow(10, bigram_prob) + "\n");
} // if
} else if(unigram_probs.containsKey(second_char) && unigram_backoff_probs.containsKey(first_char)){
// Otherwise split into unigrams and do backoff
double unigram_backoff_prob = unigram_backoff_probs
.get(first_char);
log_prob = log_prob + unigram_backoff_prob;
// System.out.println("Unigram ("+first_char+") backoff prob: "+unigram_backoff_prob);
double unigram_prob = unigram_probs.get(second_char);
log_prob = log_prob + unigram_prob;
if (verbose == true) {
double bigram_prob = unigram_backoff_prob + unigram_prob;
System.out.println("Inferred bigram prob: "
+ Math.pow(10, bigram_prob)
+ " (formed from unigram probs " + first_char
+ ": " + Math.pow(10, unigram_backoff_prob)
+ " and " + second_char + ": "
+ Math.pow(10, unigram_prob) + ")\n");
} // if
} else {
//Note: we don't penalise strings containing weird (non-printable) characters.
//If we hit one (this block), just do nothing.
//throw new RuntimeException("Language Model can't give predictions for bigram " + bigram);
log_prob += unknown_char_prob;
}
} // for
// Convert log probs to probs and take geometric mean
//TODO: if none of the chars are accepted bigrams or unigrams this function used to return 1.0...
//did averaging the prob (rather than exponentiating the average log-prob) break anything?
double avg_prob = Math.pow(10, log_prob / ((double) no_chars));
return avg_prob;
} // score
/**
* Convenience method for {@link #score(String, boolean)} with verbose flag set to false.
*/
public double score(String str) {
return score(str, false);
} // score
/**
* @return the nth most likely character to follow pre
*/
public String predict_char(String pre, int n) {
if (pre.equals(" ")) {
pre = "";
}
String key = pre + n;
if (n < 0 || n > predicted_chars) {
return null;
} else {
return context_char.get(key);
} // if/else
} // predict_char
/**
* @return the nth most likely character that a string will start with
*/
public String predict_char(int n) {
return predict_char("", n);
} // predict_char
/**
* Method which returns the probability of the nth most likely character, given a
* preceeding character (pre). Use in combination with the predict_char methods.
* @return the probability of the nth character that is most likely to appear
*/
public double predict_char_prob(String pre, int n) {
if (n < 0 || n > predicted_chars) {
return 0;
}
if (pre.equals(" ")) {
pre = "";
}
String key = pre + n;
Double prob = context_prob.get(key);
if (prob != null) {
prob = Math.pow(10, prob);
} // if
return prob;
} // predict_char_prob
/**
* Method which returns the probability of the nth most likley character at
* the start of a sentence.
* N.B. Simply calls predict_char_prob/2 with preceeding char set to "".
* @return the probability associated with the nth most likely character to start a sentence
*/
public double predict_char_prob(int n) {
return predict_char_prob("", n);
} // predict_char_prob
public boolean isMagicChar(String character){
return character.equals(START_NEW_WORD) || character.equals(END_OF_STRING) || character.equals(START_OF_STRING);
}
public boolean isEndOfSentence(String character){
return character.equals(END_OF_STRING);
}
} // LangModel
/**
* Compares values based on their values in an associated Map.
*/
class ValueComparator implements Comparator {
Map base;
/**
* Create a new comparator using a mapping of probabilities.
* The comparator will use the attached probabilities to return the
* ordering for two Strings.
* @param base a mapping of probabilities for strings.
*/
public ValueComparator(Map base) {
this.base = base;
}
// Note: this comparator imposes orderings that are inconsistent with
// equals.
public int compare(String a, String b) {
if (base.get(a) >= base.get(b)) {
return -1;
} else {
return 1;
} // returning 0 would merge keys
}
}
