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commons-math-2.1 added
| author | dwinter |
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| date | Tue, 04 Jan 2011 10:02:07 +0100 |
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<HTML> <BODY BGCOLOR="white"> <PRE> <FONT color="green">001</FONT> /*<a name="line.1"></a> <FONT color="green">002</FONT> * Licensed to the Apache Software Foundation (ASF) under one or more<a name="line.2"></a> <FONT color="green">003</FONT> * contributor license agreements. See the NOTICE file distributed with<a name="line.3"></a> <FONT color="green">004</FONT> * this work for additional information regarding copyright ownership.<a name="line.4"></a> <FONT color="green">005</FONT> * The ASF licenses this file to You under the Apache License, Version 2.0<a name="line.5"></a> <FONT color="green">006</FONT> * (the "License"); you may not use this file except in compliance with<a name="line.6"></a> <FONT color="green">007</FONT> * the License. You may obtain a copy of the License at<a name="line.7"></a> <FONT color="green">008</FONT> *<a name="line.8"></a> <FONT color="green">009</FONT> * http://www.apache.org/licenses/LICENSE-2.0<a name="line.9"></a> <FONT color="green">010</FONT> *<a name="line.10"></a> <FONT color="green">011</FONT> * Unless required by applicable law or agreed to in writing, software<a name="line.11"></a> <FONT color="green">012</FONT> * distributed under the License is distributed on an "AS IS" BASIS,<a name="line.12"></a> <FONT color="green">013</FONT> * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.<a name="line.13"></a> <FONT color="green">014</FONT> * See the License for the specific language governing permissions and<a name="line.14"></a> <FONT color="green">015</FONT> * limitations under the License.<a name="line.15"></a> <FONT color="green">016</FONT> */<a name="line.16"></a> <FONT color="green">017</FONT> <a name="line.17"></a> <FONT color="green">018</FONT> package org.apache.commons.math.random;<a name="line.18"></a> <FONT color="green">019</FONT> <a name="line.19"></a> <FONT color="green">020</FONT> import java.io.Serializable;<a name="line.20"></a> <FONT color="green">021</FONT> import java.security.MessageDigest;<a name="line.21"></a> <FONT color="green">022</FONT> import java.security.SecureRandom;<a name="line.22"></a> <FONT color="green">023</FONT> import java.security.NoSuchAlgorithmException;<a name="line.23"></a> <FONT color="green">024</FONT> import java.security.NoSuchProviderException;<a name="line.24"></a> <FONT color="green">025</FONT> import java.util.Collection;<a name="line.25"></a> <FONT color="green">026</FONT> <a name="line.26"></a> <FONT color="green">027</FONT> import org.apache.commons.math.MathRuntimeException;<a name="line.27"></a> <FONT color="green">028</FONT> import org.apache.commons.math.util.MathUtils;<a name="line.28"></a> <FONT color="green">029</FONT> <a name="line.29"></a> <FONT color="green">030</FONT> /**<a name="line.30"></a> <FONT color="green">031</FONT> * Implements the {@link RandomData} interface using a {@link RandomGenerator}<a name="line.31"></a> <FONT color="green">032</FONT> * instance to generate non-secure data and a {@link java.security.SecureRandom}<a name="line.32"></a> <FONT color="green">033</FONT> * instance to provide data for the <code>nextSecureXxx</code> methods. If no<a name="line.33"></a> <FONT color="green">034</FONT> * <code>RandomGenerator</code> is provided in the constructor, the default is<a name="line.34"></a> <FONT color="green">035</FONT> * to use a generator based on {@link java.util.Random}. To plug in a different<a name="line.35"></a> <FONT color="green">036</FONT> * implementation, either implement <code>RandomGenerator</code> directly or<a name="line.36"></a> <FONT color="green">037</FONT> * extend {@link AbstractRandomGenerator}.<a name="line.37"></a> <FONT color="green">038</FONT> * <p><a name="line.38"></a> <FONT color="green">039</FONT> * Supports reseeding the underlying pseudo-random number generator (PRNG). The<a name="line.39"></a> <FONT color="green">040</FONT> * <code>SecurityProvider</code> and <code>Algorithm</code> used by the<a name="line.40"></a> <FONT color="green">041</FONT> * <code>SecureRandom</code> instance can also be reset.<a name="line.41"></a> <FONT color="green">042</FONT> * </p><a name="line.42"></a> <FONT color="green">043</FONT> * <p><a name="line.43"></a> <FONT color="green">044</FONT> * For details on the default PRNGs, see {@link java.util.Random} and<a name="line.44"></a> <FONT color="green">045</FONT> * {@link java.security.SecureRandom}.<a name="line.45"></a> <FONT color="green">046</FONT> * </p><a name="line.46"></a> <FONT color="green">047</FONT> * <p><a name="line.47"></a> <FONT color="green">048</FONT> * <strong>Usage Notes</strong>:<a name="line.48"></a> <FONT color="green">049</FONT> * <ul><a name="line.49"></a> <FONT color="green">050</FONT> * <li><a name="line.50"></a> <FONT color="green">051</FONT> * Instance variables are used to maintain <code>RandomGenerator</code> and<a name="line.51"></a> <FONT color="green">052</FONT> * <code>SecureRandom</code> instances used in data generation. Therefore, to<a name="line.52"></a> <FONT color="green">053</FONT> * generate a random sequence of values or strings, you should use just<a name="line.53"></a> <FONT color="green">054</FONT> * <strong>one</strong> <code>RandomDataImpl</code> instance repeatedly.</li><a name="line.54"></a> <FONT color="green">055</FONT> * <li><a name="line.55"></a> <FONT color="green">056</FONT> * The "secure" methods are *much* slower. These should be used only when a<a name="line.56"></a> <FONT color="green">057</FONT> * cryptographically secure random sequence is required. A secure random<a name="line.57"></a> <FONT color="green">058</FONT> * sequence is a sequence of pseudo-random values which, in addition to being<a name="line.58"></a> <FONT color="green">059</FONT> * well-dispersed (so no subsequence of values is an any more likely than other<a name="line.59"></a> <FONT color="green">060</FONT> * subsequence of the the same length), also has the additional property that<a name="line.60"></a> <FONT color="green">061</FONT> * knowledge of values generated up to any point in the sequence does not make<a name="line.61"></a> <FONT color="green">062</FONT> * it any easier to predict subsequent values.</li><a name="line.62"></a> <FONT color="green">063</FONT> * <li><a name="line.63"></a> <FONT color="green">064</FONT> * When a new <code>RandomDataImpl</code> is created, the underlying random<a name="line.64"></a> <FONT color="green">065</FONT> * number generators are <strong>not</strong> intialized. If you do not<a name="line.65"></a> <FONT color="green">066</FONT> * explicitly seed the default non-secure generator, it is seeded with the<a name="line.66"></a> <FONT color="green">067</FONT> * current time in milliseconds on first use. The same holds for the secure<a name="line.67"></a> <FONT color="green">068</FONT> * generator. If you provide a <code>RandomGenerator</code> to the constructor,<a name="line.68"></a> <FONT color="green">069</FONT> * however, this generator is not reseeded by the constructor nor is it reseeded<a name="line.69"></a> <FONT color="green">070</FONT> * on first use.</li><a name="line.70"></a> <FONT color="green">071</FONT> * <li><a name="line.71"></a> <FONT color="green">072</FONT> * The <code>reSeed</code> and <code>reSeedSecure</code> methods delegate to the<a name="line.72"></a> <FONT color="green">073</FONT> * corresponding methods on the underlying <code>RandomGenerator</code> and<a name="line.73"></a> <FONT color="green">074</FONT> * <code>SecureRandom</code> instances. Therefore, <code>reSeed(long)</code><a name="line.74"></a> <FONT color="green">075</FONT> * fully resets the initial state of the non-secure random number generator (so<a name="line.75"></a> <FONT color="green">076</FONT> * that reseeding with a specific value always results in the same subsequent<a name="line.76"></a> <FONT color="green">077</FONT> * random sequence); whereas reSeedSecure(long) does <strong>not</strong><a name="line.77"></a> <FONT color="green">078</FONT> * reinitialize the secure random number generator (so secure sequences started<a name="line.78"></a> <FONT color="green">079</FONT> * with calls to reseedSecure(long) won't be identical).</li><a name="line.79"></a> <FONT color="green">080</FONT> * <li><a name="line.80"></a> <FONT color="green">081</FONT> * This implementation is not synchronized.<a name="line.81"></a> <FONT color="green">082</FONT> * </ul><a name="line.82"></a> <FONT color="green">083</FONT> * </p><a name="line.83"></a> <FONT color="green">084</FONT> *<a name="line.84"></a> <FONT color="green">085</FONT> * @version $Revision: 831510 $ $Date: 2009-10-30 22:30:18 -0400 (Fri, 30 Oct 2009) $<a name="line.85"></a> <FONT color="green">086</FONT> */<a name="line.86"></a> <FONT color="green">087</FONT> public class RandomDataImpl implements RandomData, Serializable {<a name="line.87"></a> <FONT color="green">088</FONT> <a name="line.88"></a> <FONT color="green">089</FONT> /** Serializable version identifier */<a name="line.89"></a> <FONT color="green">090</FONT> private static final long serialVersionUID = -626730818244969716L;<a name="line.90"></a> <FONT color="green">091</FONT> <a name="line.91"></a> <FONT color="green">092</FONT> /** underlying random number generator */<a name="line.92"></a> <FONT color="green">093</FONT> private RandomGenerator rand = null;<a name="line.93"></a> <FONT color="green">094</FONT> <a name="line.94"></a> <FONT color="green">095</FONT> /** underlying secure random number generator */<a name="line.95"></a> <FONT color="green">096</FONT> private SecureRandom secRand = null;<a name="line.96"></a> <FONT color="green">097</FONT> <a name="line.97"></a> <FONT color="green">098</FONT> /**<a name="line.98"></a> <FONT color="green">099</FONT> * Construct a RandomDataImpl.<a name="line.99"></a> <FONT color="green">100</FONT> */<a name="line.100"></a> <FONT color="green">101</FONT> public RandomDataImpl() {<a name="line.101"></a> <FONT color="green">102</FONT> }<a name="line.102"></a> <FONT color="green">103</FONT> <a name="line.103"></a> <FONT color="green">104</FONT> /**<a name="line.104"></a> <FONT color="green">105</FONT> * Construct a RandomDataImpl using the supplied {@link RandomGenerator} as<a name="line.105"></a> <FONT color="green">106</FONT> * the source of (non-secure) random data.<a name="line.106"></a> <FONT color="green">107</FONT> *<a name="line.107"></a> <FONT color="green">108</FONT> * @param rand<a name="line.108"></a> <FONT color="green">109</FONT> * the source of (non-secure) random data<a name="line.109"></a> <FONT color="green">110</FONT> * @since 1.1<a name="line.110"></a> <FONT color="green">111</FONT> */<a name="line.111"></a> <FONT color="green">112</FONT> public RandomDataImpl(RandomGenerator rand) {<a name="line.112"></a> <FONT color="green">113</FONT> super();<a name="line.113"></a> <FONT color="green">114</FONT> this.rand = rand;<a name="line.114"></a> <FONT color="green">115</FONT> }<a name="line.115"></a> <FONT color="green">116</FONT> <a name="line.116"></a> <FONT color="green">117</FONT> /**<a name="line.117"></a> <FONT color="green">118</FONT> * {@inheritDoc}<a name="line.118"></a> <FONT color="green">119</FONT> * <p><a name="line.119"></a> <FONT color="green">120</FONT> * <strong>Algorithm Description:</strong> hex strings are generated using a<a name="line.120"></a> <FONT color="green">121</FONT> * 2-step process.<a name="line.121"></a> <FONT color="green">122</FONT> * <ol><a name="line.122"></a> <FONT color="green">123</FONT> * <li><a name="line.123"></a> <FONT color="green">124</FONT> * len/2+1 binary bytes are generated using the underlying Random</li><a name="line.124"></a> <FONT color="green">125</FONT> * <li><a name="line.125"></a> <FONT color="green">126</FONT> * Each binary byte is translated into 2 hex digits</li><a name="line.126"></a> <FONT color="green">127</FONT> * </ol><a name="line.127"></a> <FONT color="green">128</FONT> * </p><a name="line.128"></a> <FONT color="green">129</FONT> *<a name="line.129"></a> <FONT color="green">130</FONT> * @param len<a name="line.130"></a> <FONT color="green">131</FONT> * the desired string length.<a name="line.131"></a> <FONT color="green">132</FONT> * @return the random string.<a name="line.132"></a> <FONT color="green">133</FONT> */<a name="line.133"></a> <FONT color="green">134</FONT> public String nextHexString(int len) {<a name="line.134"></a> <FONT color="green">135</FONT> if (len <= 0) {<a name="line.135"></a> <FONT color="green">136</FONT> throw MathRuntimeException.createIllegalArgumentException(<a name="line.136"></a> <FONT color="green">137</FONT> "length must be positive ({0})", len);<a name="line.137"></a> <FONT color="green">138</FONT> }<a name="line.138"></a> <FONT color="green">139</FONT> <a name="line.139"></a> <FONT color="green">140</FONT> // Get a random number generator<a name="line.140"></a> <FONT color="green">141</FONT> RandomGenerator ran = getRan();<a name="line.141"></a> <FONT color="green">142</FONT> <a name="line.142"></a> <FONT color="green">143</FONT> // Initialize output buffer<a name="line.143"></a> <FONT color="green">144</FONT> StringBuffer outBuffer = new StringBuffer();<a name="line.144"></a> <FONT color="green">145</FONT> <a name="line.145"></a> <FONT color="green">146</FONT> // Get int(len/2)+1 random bytes<a name="line.146"></a> <FONT color="green">147</FONT> byte[] randomBytes = new byte[(len / 2) + 1];<a name="line.147"></a> <FONT color="green">148</FONT> ran.nextBytes(randomBytes);<a name="line.148"></a> <FONT color="green">149</FONT> <a name="line.149"></a> <FONT color="green">150</FONT> // Convert each byte to 2 hex digits<a name="line.150"></a> <FONT color="green">151</FONT> for (int i = 0; i < randomBytes.length; i++) {<a name="line.151"></a> <FONT color="green">152</FONT> Integer c = Integer.valueOf(randomBytes[i]);<a name="line.152"></a> <FONT color="green">153</FONT> <a name="line.153"></a> <FONT color="green">154</FONT> /*<a name="line.154"></a> <FONT color="green">155</FONT> * Add 128 to byte value to make interval 0-255 before doing hex<a name="line.155"></a> <FONT color="green">156</FONT> * conversion. This guarantees <= 2 hex digits from toHexString()<a name="line.156"></a> <FONT color="green">157</FONT> * toHexString would otherwise add 2^32 to negative arguments.<a name="line.157"></a> <FONT color="green">158</FONT> */<a name="line.158"></a> <FONT color="green">159</FONT> String hex = Integer.toHexString(c.intValue() + 128);<a name="line.159"></a> <FONT color="green">160</FONT> <a name="line.160"></a> <FONT color="green">161</FONT> // Make sure we add 2 hex digits for each byte<a name="line.161"></a> <FONT color="green">162</FONT> if (hex.length() == 1) {<a name="line.162"></a> <FONT color="green">163</FONT> hex = "0" + hex;<a name="line.163"></a> <FONT color="green">164</FONT> }<a name="line.164"></a> <FONT color="green">165</FONT> outBuffer.append(hex);<a name="line.165"></a> <FONT color="green">166</FONT> }<a name="line.166"></a> <FONT color="green">167</FONT> return outBuffer.toString().substring(0, len);<a name="line.167"></a> <FONT color="green">168</FONT> }<a name="line.168"></a> <FONT color="green">169</FONT> <a name="line.169"></a> <FONT color="green">170</FONT> /**<a name="line.170"></a> <FONT color="green">171</FONT> * Generate a random int value uniformly distributed between<a name="line.171"></a> <FONT color="green">172</FONT> * <code>lower</code> and <code>upper</code>, inclusive.<a name="line.172"></a> <FONT color="green">173</FONT> *<a name="line.173"></a> <FONT color="green">174</FONT> * @param lower<a name="line.174"></a> <FONT color="green">175</FONT> * the lower bound.<a name="line.175"></a> <FONT color="green">176</FONT> * @param upper<a name="line.176"></a> <FONT color="green">177</FONT> * the upper bound.<a name="line.177"></a> <FONT color="green">178</FONT> * @return the random integer.<a name="line.178"></a> <FONT color="green">179</FONT> */<a name="line.179"></a> <FONT color="green">180</FONT> public int nextInt(int lower, int upper) {<a name="line.180"></a> <FONT color="green">181</FONT> if (lower >= upper) {<a name="line.181"></a> <FONT color="green">182</FONT> throw MathRuntimeException.createIllegalArgumentException(<a name="line.182"></a> <FONT color="green">183</FONT> "upper bound ({0}) must be greater than lower bound ({1})",<a name="line.183"></a> <FONT color="green">184</FONT> upper, lower);<a name="line.184"></a> <FONT color="green">185</FONT> }<a name="line.185"></a> <FONT color="green">186</FONT> double r = getRan().nextDouble();<a name="line.186"></a> <FONT color="green">187</FONT> return (int) ((r * upper) + ((1.0 - r) * lower) + r);<a name="line.187"></a> <FONT color="green">188</FONT> }<a name="line.188"></a> <FONT color="green">189</FONT> <a name="line.189"></a> <FONT color="green">190</FONT> /**<a name="line.190"></a> <FONT color="green">191</FONT> * Generate a random long value uniformly distributed between<a name="line.191"></a> <FONT color="green">192</FONT> * <code>lower</code> and <code>upper</code>, inclusive.<a name="line.192"></a> <FONT color="green">193</FONT> *<a name="line.193"></a> <FONT color="green">194</FONT> * @param lower<a name="line.194"></a> <FONT color="green">195</FONT> * the lower bound.<a name="line.195"></a> <FONT color="green">196</FONT> * @param upper<a name="line.196"></a> <FONT color="green">197</FONT> * the upper bound.<a name="line.197"></a> <FONT color="green">198</FONT> * @return the random integer.<a name="line.198"></a> <FONT color="green">199</FONT> */<a name="line.199"></a> <FONT color="green">200</FONT> public long nextLong(long lower, long upper) {<a name="line.200"></a> <FONT color="green">201</FONT> if (lower >= upper) {<a name="line.201"></a> <FONT color="green">202</FONT> throw MathRuntimeException.createIllegalArgumentException(<a name="line.202"></a> <FONT color="green">203</FONT> "upper bound ({0}) must be greater than lower bound ({1})",<a name="line.203"></a> <FONT color="green">204</FONT> upper, lower);<a name="line.204"></a> <FONT color="green">205</FONT> }<a name="line.205"></a> <FONT color="green">206</FONT> double r = getRan().nextDouble();<a name="line.206"></a> <FONT color="green">207</FONT> return (long) ((r * upper) + ((1.0 - r) * lower) + r);<a name="line.207"></a> <FONT color="green">208</FONT> }<a name="line.208"></a> <FONT color="green">209</FONT> <a name="line.209"></a> <FONT color="green">210</FONT> /**<a name="line.210"></a> <FONT color="green">211</FONT> * {@inheritDoc}<a name="line.211"></a> <FONT color="green">212</FONT> * <p><a name="line.212"></a> <FONT color="green">213</FONT> * <strong>Algorithm Description:</strong> hex strings are generated in<a name="line.213"></a> <FONT color="green">214</FONT> * 40-byte segments using a 3-step process.<a name="line.214"></a> <FONT color="green">215</FONT> * <ol><a name="line.215"></a> <FONT color="green">216</FONT> * <li><a name="line.216"></a> <FONT color="green">217</FONT> * 20 random bytes are generated using the underlying<a name="line.217"></a> <FONT color="green">218</FONT> * <code>SecureRandom</code>.</li><a name="line.218"></a> <FONT color="green">219</FONT> * <li><a name="line.219"></a> <FONT color="green">220</FONT> * SHA-1 hash is applied to yield a 20-byte binary digest.</li><a name="line.220"></a> <FONT color="green">221</FONT> * <li><a name="line.221"></a> <FONT color="green">222</FONT> * Each byte of the binary digest is converted to 2 hex digits.</li><a name="line.222"></a> <FONT color="green">223</FONT> * </ol><a name="line.223"></a> <FONT color="green">224</FONT> * </p><a name="line.224"></a> <FONT color="green">225</FONT> *<a name="line.225"></a> <FONT color="green">226</FONT> * @param len<a name="line.226"></a> <FONT color="green">227</FONT> * the length of the generated string<a name="line.227"></a> <FONT color="green">228</FONT> * @return the random string<a name="line.228"></a> <FONT color="green">229</FONT> */<a name="line.229"></a> <FONT color="green">230</FONT> public String nextSecureHexString(int len) {<a name="line.230"></a> <FONT color="green">231</FONT> if (len <= 0) {<a name="line.231"></a> <FONT color="green">232</FONT> throw MathRuntimeException.createIllegalArgumentException(<a name="line.232"></a> <FONT color="green">233</FONT> "length must be positive ({0})", len);<a name="line.233"></a> <FONT color="green">234</FONT> }<a name="line.234"></a> <FONT color="green">235</FONT> <a name="line.235"></a> <FONT color="green">236</FONT> // Get SecureRandom and setup Digest provider<a name="line.236"></a> <FONT color="green">237</FONT> SecureRandom secRan = getSecRan();<a name="line.237"></a> <FONT color="green">238</FONT> MessageDigest alg = null;<a name="line.238"></a> <FONT color="green">239</FONT> try {<a name="line.239"></a> <FONT color="green">240</FONT> alg = MessageDigest.getInstance("SHA-1");<a name="line.240"></a> <FONT color="green">241</FONT> } catch (NoSuchAlgorithmException ex) {<a name="line.241"></a> <FONT color="green">242</FONT> // this should never happen<a name="line.242"></a> <FONT color="green">243</FONT> throw MathRuntimeException.createInternalError(ex);<a name="line.243"></a> <FONT color="green">244</FONT> }<a name="line.244"></a> <FONT color="green">245</FONT> alg.reset();<a name="line.245"></a> <FONT color="green">246</FONT> <a name="line.246"></a> <FONT color="green">247</FONT> // Compute number of iterations required (40 bytes each)<a name="line.247"></a> <FONT color="green">248</FONT> int numIter = (len / 40) + 1;<a name="line.248"></a> <FONT color="green">249</FONT> <a name="line.249"></a> <FONT color="green">250</FONT> StringBuffer outBuffer = new StringBuffer();<a name="line.250"></a> <FONT color="green">251</FONT> for (int iter = 1; iter < numIter + 1; iter++) {<a name="line.251"></a> <FONT color="green">252</FONT> byte[] randomBytes = new byte[40];<a name="line.252"></a> <FONT color="green">253</FONT> secRan.nextBytes(randomBytes);<a name="line.253"></a> <FONT color="green">254</FONT> alg.update(randomBytes);<a name="line.254"></a> <FONT color="green">255</FONT> <a name="line.255"></a> <FONT color="green">256</FONT> // Compute hash -- will create 20-byte binary hash<a name="line.256"></a> <FONT color="green">257</FONT> byte hash[] = alg.digest();<a name="line.257"></a> <FONT color="green">258</FONT> <a name="line.258"></a> <FONT color="green">259</FONT> // Loop over the hash, converting each byte to 2 hex digits<a name="line.259"></a> <FONT color="green">260</FONT> for (int i = 0; i < hash.length; i++) {<a name="line.260"></a> <FONT color="green">261</FONT> Integer c = Integer.valueOf(hash[i]);<a name="line.261"></a> <FONT color="green">262</FONT> <a name="line.262"></a> <FONT color="green">263</FONT> /*<a name="line.263"></a> <FONT color="green">264</FONT> * Add 128 to byte value to make interval 0-255 This guarantees<a name="line.264"></a> <FONT color="green">265</FONT> * <= 2 hex digits from toHexString() toHexString would<a name="line.265"></a> <FONT color="green">266</FONT> * otherwise add 2^32 to negative arguments<a name="line.266"></a> <FONT color="green">267</FONT> */<a name="line.267"></a> <FONT color="green">268</FONT> String hex = Integer.toHexString(c.intValue() + 128);<a name="line.268"></a> <FONT color="green">269</FONT> <a name="line.269"></a> <FONT color="green">270</FONT> // Keep strings uniform length -- guarantees 40 bytes<a name="line.270"></a> <FONT color="green">271</FONT> if (hex.length() == 1) {<a name="line.271"></a> <FONT color="green">272</FONT> hex = "0" + hex;<a name="line.272"></a> <FONT color="green">273</FONT> }<a name="line.273"></a> <FONT color="green">274</FONT> outBuffer.append(hex);<a name="line.274"></a> <FONT color="green">275</FONT> }<a name="line.275"></a> <FONT color="green">276</FONT> }<a name="line.276"></a> <FONT color="green">277</FONT> return outBuffer.toString().substring(0, len);<a name="line.277"></a> <FONT color="green">278</FONT> }<a name="line.278"></a> <FONT color="green">279</FONT> <a name="line.279"></a> <FONT color="green">280</FONT> /**<a name="line.280"></a> <FONT color="green">281</FONT> * Generate a random int value uniformly distributed between<a name="line.281"></a> <FONT color="green">282</FONT> * <code>lower</code> and <code>upper</code>, inclusive. This algorithm uses<a name="line.282"></a> <FONT color="green">283</FONT> * a secure random number generator.<a name="line.283"></a> <FONT color="green">284</FONT> *<a name="line.284"></a> <FONT color="green">285</FONT> * @param lower<a name="line.285"></a> <FONT color="green">286</FONT> * the lower bound.<a name="line.286"></a> <FONT color="green">287</FONT> * @param upper<a name="line.287"></a> <FONT color="green">288</FONT> * the upper bound.<a name="line.288"></a> <FONT color="green">289</FONT> * @return the random integer.<a name="line.289"></a> <FONT color="green">290</FONT> */<a name="line.290"></a> <FONT color="green">291</FONT> public int nextSecureInt(int lower, int upper) {<a name="line.291"></a> <FONT color="green">292</FONT> if (lower >= upper) {<a name="line.292"></a> <FONT color="green">293</FONT> throw MathRuntimeException.createIllegalArgumentException(<a name="line.293"></a> <FONT color="green">294</FONT> "upper bound ({0}) must be greater than lower bound ({1})",<a name="line.294"></a> <FONT color="green">295</FONT> upper, lower);<a name="line.295"></a> <FONT color="green">296</FONT> }<a name="line.296"></a> <FONT color="green">297</FONT> SecureRandom sec = getSecRan();<a name="line.297"></a> <FONT color="green">298</FONT> return lower + (int) (sec.nextDouble() * (upper - lower + 1));<a name="line.298"></a> <FONT color="green">299</FONT> }<a name="line.299"></a> <FONT color="green">300</FONT> <a name="line.300"></a> <FONT color="green">301</FONT> /**<a name="line.301"></a> <FONT color="green">302</FONT> * Generate a random long value uniformly distributed between<a name="line.302"></a> <FONT color="green">303</FONT> * <code>lower</code> and <code>upper</code>, inclusive. This algorithm uses<a name="line.303"></a> <FONT color="green">304</FONT> * a secure random number generator.<a name="line.304"></a> <FONT color="green">305</FONT> *<a name="line.305"></a> <FONT color="green">306</FONT> * @param lower<a name="line.306"></a> <FONT color="green">307</FONT> * the lower bound.<a name="line.307"></a> <FONT color="green">308</FONT> * @param upper<a name="line.308"></a> <FONT color="green">309</FONT> * the upper bound.<a name="line.309"></a> <FONT color="green">310</FONT> * @return the random integer.<a name="line.310"></a> <FONT color="green">311</FONT> */<a name="line.311"></a> <FONT color="green">312</FONT> public long nextSecureLong(long lower, long upper) {<a name="line.312"></a> <FONT color="green">313</FONT> if (lower >= upper) {<a name="line.313"></a> <FONT color="green">314</FONT> throw MathRuntimeException.createIllegalArgumentException(<a name="line.314"></a> <FONT color="green">315</FONT> "upper bound ({0}) must be greater than lower bound ({1})",<a name="line.315"></a> <FONT color="green">316</FONT> upper, lower);<a name="line.316"></a> <FONT color="green">317</FONT> }<a name="line.317"></a> <FONT color="green">318</FONT> SecureRandom sec = getSecRan();<a name="line.318"></a> <FONT color="green">319</FONT> return lower + (long) (sec.nextDouble() * (upper - lower + 1));<a name="line.319"></a> <FONT color="green">320</FONT> }<a name="line.320"></a> <FONT color="green">321</FONT> <a name="line.321"></a> <FONT color="green">322</FONT> /**<a name="line.322"></a> <FONT color="green">323</FONT> * {@inheritDoc}<a name="line.323"></a> <FONT color="green">324</FONT> * <p><a name="line.324"></a> <FONT color="green">325</FONT> * <strong>Algorithm Description</strong>:<a name="line.325"></a> <FONT color="green">326</FONT> * <ul><li> For small means, uses simulation of a Poisson process<a name="line.326"></a> <FONT color="green">327</FONT> * using Uniform deviates, as described<a name="line.327"></a> <FONT color="green">328</FONT> * <a href="http://irmi.epfl.ch/cmos/Pmmi/interactive/rng7.htm"> here.</a><a name="line.328"></a> <FONT color="green">329</FONT> * The Poisson process (and hence value returned) is bounded by 1000 * mean.</li><a name="line.329"></a> <FONT color="green">330</FONT> *<a name="line.330"></a> <FONT color="green">331</FONT> * <li> For large means, uses the rejection algorithm described in <br/><a name="line.331"></a> <FONT color="green">332</FONT> * Devroye, Luc. (1981).<i>The Computer Generation of Poisson Random Variables</i><a name="line.332"></a> <FONT color="green">333</FONT> * <strong>Computing</strong> vol. 26 pp. 197-207.</li></ul></p><a name="line.333"></a> <FONT color="green">334</FONT> *<a name="line.334"></a> <FONT color="green">335</FONT> * @param mean mean of the Poisson distribution.<a name="line.335"></a> <FONT color="green">336</FONT> * @return the random Poisson value.<a name="line.336"></a> <FONT color="green">337</FONT> */<a name="line.337"></a> <FONT color="green">338</FONT> public long nextPoisson(double mean) {<a name="line.338"></a> <FONT color="green">339</FONT> if (mean <= 0) {<a name="line.339"></a> <FONT color="green">340</FONT> throw MathRuntimeException.createIllegalArgumentException(<a name="line.340"></a> <FONT color="green">341</FONT> "the Poisson mean must be positive ({0})", mean);<a name="line.341"></a> <FONT color="green">342</FONT> }<a name="line.342"></a> <FONT color="green">343</FONT> <a name="line.343"></a> <FONT color="green">344</FONT> final RandomGenerator generator = getRan();<a name="line.344"></a> <FONT color="green">345</FONT> <a name="line.345"></a> <FONT color="green">346</FONT> final double pivot = 40.0d;<a name="line.346"></a> <FONT color="green">347</FONT> if (mean < pivot) {<a name="line.347"></a> <FONT color="green">348</FONT> double p = Math.exp(-mean);<a name="line.348"></a> <FONT color="green">349</FONT> long n = 0;<a name="line.349"></a> <FONT color="green">350</FONT> double r = 1.0d;<a name="line.350"></a> <FONT color="green">351</FONT> double rnd = 1.0d;<a name="line.351"></a> <FONT color="green">352</FONT> <a name="line.352"></a> <FONT color="green">353</FONT> while (n < 1000 * mean) {<a name="line.353"></a> <FONT color="green">354</FONT> rnd = generator.nextDouble();<a name="line.354"></a> <FONT color="green">355</FONT> r = r * rnd;<a name="line.355"></a> <FONT color="green">356</FONT> if (r >= p) {<a name="line.356"></a> <FONT color="green">357</FONT> n++;<a name="line.357"></a> <FONT color="green">358</FONT> } else {<a name="line.358"></a> <FONT color="green">359</FONT> return n;<a name="line.359"></a> <FONT color="green">360</FONT> }<a name="line.360"></a> <FONT color="green">361</FONT> }<a name="line.361"></a> <FONT color="green">362</FONT> return n;<a name="line.362"></a> <FONT color="green">363</FONT> } else {<a name="line.363"></a> <FONT color="green">364</FONT> final double lambda = Math.floor(mean);<a name="line.364"></a> <FONT color="green">365</FONT> final double lambdaFractional = mean - lambda;<a name="line.365"></a> <FONT color="green">366</FONT> final double logLambda = Math.log(lambda);<a name="line.366"></a> <FONT color="green">367</FONT> final double logLambdaFactorial = MathUtils.factorialLog((int) lambda);<a name="line.367"></a> <FONT color="green">368</FONT> final long y2 = lambdaFractional < Double.MIN_VALUE ? 0 : nextPoisson(lambdaFractional);<a name="line.368"></a> <FONT color="green">369</FONT> final double delta = Math.sqrt(lambda * Math.log(32 * lambda / Math.PI + 1));<a name="line.369"></a> <FONT color="green">370</FONT> final double halfDelta = delta / 2;<a name="line.370"></a> <FONT color="green">371</FONT> final double twolpd = 2 * lambda + delta;<a name="line.371"></a> <FONT color="green">372</FONT> final double a1 = Math.sqrt(Math.PI * twolpd) * Math.exp(1 / 8 * lambda);<a name="line.372"></a> <FONT color="green">373</FONT> final double a2 = (twolpd / delta) * Math.exp(-delta * (1 + delta) / twolpd);<a name="line.373"></a> <FONT color="green">374</FONT> final double aSum = a1 + a2 + 1;<a name="line.374"></a> <FONT color="green">375</FONT> final double p1 = a1 / aSum;<a name="line.375"></a> <FONT color="green">376</FONT> final double p2 = a2 / aSum;<a name="line.376"></a> <FONT color="green">377</FONT> final double c1 = 1 / (8 * lambda);<a name="line.377"></a> <FONT color="green">378</FONT> <a name="line.378"></a> <FONT color="green">379</FONT> double x = 0;<a name="line.379"></a> <FONT color="green">380</FONT> double y = 0;<a name="line.380"></a> <FONT color="green">381</FONT> double v = 0;<a name="line.381"></a> <FONT color="green">382</FONT> int a = 0;<a name="line.382"></a> <FONT color="green">383</FONT> double t = 0;<a name="line.383"></a> <FONT color="green">384</FONT> double qr = 0;<a name="line.384"></a> <FONT color="green">385</FONT> double qa = 0;<a name="line.385"></a> <FONT color="green">386</FONT> for (;;) {<a name="line.386"></a> <FONT color="green">387</FONT> final double u = nextUniform(0.0, 1);<a name="line.387"></a> <FONT color="green">388</FONT> if (u <= p1) {<a name="line.388"></a> <FONT color="green">389</FONT> final double n = nextGaussian(0d, 1d);<a name="line.389"></a> <FONT color="green">390</FONT> x = n * Math.sqrt(lambda + halfDelta) - 0.5d;<a name="line.390"></a> <FONT color="green">391</FONT> if (x > delta || x < -lambda) {<a name="line.391"></a> <FONT color="green">392</FONT> continue;<a name="line.392"></a> <FONT color="green">393</FONT> }<a name="line.393"></a> <FONT color="green">394</FONT> y = x < 0 ? Math.floor(x) : Math.ceil(x);<a name="line.394"></a> <FONT color="green">395</FONT> final double e = nextExponential(1d);<a name="line.395"></a> <FONT color="green">396</FONT> v = -e - (n * n / 2) + c1;<a name="line.396"></a> <FONT color="green">397</FONT> } else {<a name="line.397"></a> <FONT color="green">398</FONT> if (u > p1 + p2) {<a name="line.398"></a> <FONT color="green">399</FONT> y = lambda;<a name="line.399"></a> <FONT color="green">400</FONT> break;<a name="line.400"></a> <FONT color="green">401</FONT> } else {<a name="line.401"></a> <FONT color="green">402</FONT> x = delta + (twolpd / delta) * nextExponential(1d);<a name="line.402"></a> <FONT color="green">403</FONT> y = Math.ceil(x);<a name="line.403"></a> <FONT color="green">404</FONT> v = -nextExponential(1d) - delta * (x + 1) / twolpd;<a name="line.404"></a> <FONT color="green">405</FONT> }<a name="line.405"></a> <FONT color="green">406</FONT> }<a name="line.406"></a> <FONT color="green">407</FONT> a = x < 0 ? 1 : 0;<a name="line.407"></a> <FONT color="green">408</FONT> t = y * (y + 1) / (2 * lambda);<a name="line.408"></a> <FONT color="green">409</FONT> if (v < -t && a == 0) {<a name="line.409"></a> <FONT color="green">410</FONT> y = lambda + y;<a name="line.410"></a> <FONT color="green">411</FONT> break;<a name="line.411"></a> <FONT color="green">412</FONT> }<a name="line.412"></a> <FONT color="green">413</FONT> qr = t * ((2 * y + 1) / (6 * lambda) - 1);<a name="line.413"></a> <FONT color="green">414</FONT> qa = qr - (t * t) / (3 * (lambda + a * (y + 1)));<a name="line.414"></a> <FONT color="green">415</FONT> if (v < qa) {<a name="line.415"></a> <FONT color="green">416</FONT> y = lambda + y;<a name="line.416"></a> <FONT color="green">417</FONT> break;<a name="line.417"></a> <FONT color="green">418</FONT> }<a name="line.418"></a> <FONT color="green">419</FONT> if (v > qr) {<a name="line.419"></a> <FONT color="green">420</FONT> continue;<a name="line.420"></a> <FONT color="green">421</FONT> }<a name="line.421"></a> <FONT color="green">422</FONT> if (v < y * logLambda - MathUtils.factorialLog((int) (y + lambda)) + logLambdaFactorial) {<a name="line.422"></a> <FONT color="green">423</FONT> y = lambda + y;<a name="line.423"></a> <FONT color="green">424</FONT> break;<a name="line.424"></a> <FONT color="green">425</FONT> }<a name="line.425"></a> <FONT color="green">426</FONT> }<a name="line.426"></a> <FONT color="green">427</FONT> return y2 + (long) y;<a name="line.427"></a> <FONT color="green">428</FONT> }<a name="line.428"></a> <FONT color="green">429</FONT> }<a name="line.429"></a> <FONT color="green">430</FONT> <a name="line.430"></a> <FONT color="green">431</FONT> /**<a name="line.431"></a> <FONT color="green">432</FONT> * Generate a random value from a Normal (a.k.a. Gaussian) distribution with<a name="line.432"></a> <FONT color="green">433</FONT> * the given mean, <code>mu</code> and the given standard deviation,<a name="line.433"></a> <FONT color="green">434</FONT> * <code>sigma</code>.<a name="line.434"></a> <FONT color="green">435</FONT> *<a name="line.435"></a> <FONT color="green">436</FONT> * @param mu<a name="line.436"></a> <FONT color="green">437</FONT> * the mean of the distribution<a name="line.437"></a> <FONT color="green">438</FONT> * @param sigma<a name="line.438"></a> <FONT color="green">439</FONT> * the standard deviation of the distribution<a name="line.439"></a> <FONT color="green">440</FONT> * @return the random Normal value<a name="line.440"></a> <FONT color="green">441</FONT> */<a name="line.441"></a> <FONT color="green">442</FONT> public double nextGaussian(double mu, double sigma) {<a name="line.442"></a> <FONT color="green">443</FONT> if (sigma <= 0) {<a name="line.443"></a> <FONT color="green">444</FONT> throw MathRuntimeException.createIllegalArgumentException(<a name="line.444"></a> <FONT color="green">445</FONT> "standard deviation must be positive ({0})", sigma);<a name="line.445"></a> <FONT color="green">446</FONT> }<a name="line.446"></a> <FONT color="green">447</FONT> return sigma * getRan().nextGaussian() + mu;<a name="line.447"></a> <FONT color="green">448</FONT> }<a name="line.448"></a> <FONT color="green">449</FONT> <a name="line.449"></a> <FONT color="green">450</FONT> /**<a name="line.450"></a> <FONT color="green">451</FONT> * Returns a random value from an Exponential distribution with the given<a name="line.451"></a> <FONT color="green">452</FONT> * mean.<a name="line.452"></a> <FONT color="green">453</FONT> * <p><a name="line.453"></a> <FONT color="green">454</FONT> * <strong>Algorithm Description</strong>: Uses the <a<a name="line.454"></a> <FONT color="green">455</FONT> * href="http://www.jesus.ox.ac.uk/~clifford/a5/chap1/node5.html"> Inversion<a name="line.455"></a> <FONT color="green">456</FONT> * Method</a> to generate exponentially distributed random values from<a name="line.456"></a> <FONT color="green">457</FONT> * uniform deviates.<a name="line.457"></a> <FONT color="green">458</FONT> * </p><a name="line.458"></a> <FONT color="green">459</FONT> *<a name="line.459"></a> <FONT color="green">460</FONT> * @param mean the mean of the distribution<a name="line.460"></a> <FONT color="green">461</FONT> * @return the random Exponential value<a name="line.461"></a> <FONT color="green">462</FONT> */<a name="line.462"></a> <FONT color="green">463</FONT> public double nextExponential(double mean) {<a name="line.463"></a> <FONT color="green">464</FONT> if (mean <= 0.0) {<a name="line.464"></a> <FONT color="green">465</FONT> throw MathRuntimeException.createIllegalArgumentException(<a name="line.465"></a> <FONT color="green">466</FONT> "mean must be positive ({0})", mean);<a name="line.466"></a> <FONT color="green">467</FONT> }<a name="line.467"></a> <FONT color="green">468</FONT> final RandomGenerator generator = getRan();<a name="line.468"></a> <FONT color="green">469</FONT> double unif = generator.nextDouble();<a name="line.469"></a> <FONT color="green">470</FONT> while (unif == 0.0d) {<a name="line.470"></a> <FONT color="green">471</FONT> unif = generator.nextDouble();<a name="line.471"></a> <FONT color="green">472</FONT> }<a name="line.472"></a> <FONT color="green">473</FONT> return -mean * Math.log(unif);<a name="line.473"></a> <FONT color="green">474</FONT> }<a name="line.474"></a> <FONT color="green">475</FONT> <a name="line.475"></a> <FONT color="green">476</FONT> /**<a name="line.476"></a> <FONT color="green">477</FONT> * {@inheritDoc}<a name="line.477"></a> <FONT color="green">478</FONT> * <p><a name="line.478"></a> <FONT color="green">479</FONT> * <strong>Algorithm Description</strong>: scales the output of<a name="line.479"></a> <FONT color="green">480</FONT> * Random.nextDouble(), but rejects 0 values (i.e., will generate another<a name="line.480"></a> <FONT color="green">481</FONT> * random double if Random.nextDouble() returns 0). This is necessary to<a name="line.481"></a> <FONT color="green">482</FONT> * provide a symmetric output interval (both endpoints excluded).<a name="line.482"></a> <FONT color="green">483</FONT> * </p><a name="line.483"></a> <FONT color="green">484</FONT> *<a name="line.484"></a> <FONT color="green">485</FONT> * @param lower<a name="line.485"></a> <FONT color="green">486</FONT> * the lower bound.<a name="line.486"></a> <FONT color="green">487</FONT> * @param upper<a name="line.487"></a> <FONT color="green">488</FONT> * the upper bound.<a name="line.488"></a> <FONT color="green">489</FONT> * @return a uniformly distributed random value from the interval (lower,<a name="line.489"></a> <FONT color="green">490</FONT> * upper)<a name="line.490"></a> <FONT color="green">491</FONT> */<a name="line.491"></a> <FONT color="green">492</FONT> public double nextUniform(double lower, double upper) {<a name="line.492"></a> <FONT color="green">493</FONT> if (lower >= upper) {<a name="line.493"></a> <FONT color="green">494</FONT> throw MathRuntimeException.createIllegalArgumentException(<a name="line.494"></a> <FONT color="green">495</FONT> "upper bound ({0}) must be greater than lower bound ({1})",<a name="line.495"></a> <FONT color="green">496</FONT> upper, lower);<a name="line.496"></a> <FONT color="green">497</FONT> }<a name="line.497"></a> <FONT color="green">498</FONT> final RandomGenerator generator = getRan();<a name="line.498"></a> <FONT color="green">499</FONT> <a name="line.499"></a> <FONT color="green">500</FONT> // ensure nextDouble() isn't 0.0<a name="line.500"></a> <FONT color="green">501</FONT> double u = generator.nextDouble();<a name="line.501"></a> <FONT color="green">502</FONT> while (u <= 0.0) {<a name="line.502"></a> <FONT color="green">503</FONT> u = generator.nextDouble();<a name="line.503"></a> <FONT color="green">504</FONT> }<a name="line.504"></a> <FONT color="green">505</FONT> <a name="line.505"></a> <FONT color="green">506</FONT> return lower + u * (upper - lower);<a name="line.506"></a> <FONT color="green">507</FONT> }<a name="line.507"></a> <FONT color="green">508</FONT> <a name="line.508"></a> <FONT color="green">509</FONT> /**<a name="line.509"></a> <FONT color="green">510</FONT> * Returns the RandomGenerator used to generate non-secure random data.<a name="line.510"></a> <FONT color="green">511</FONT> * <p><a name="line.511"></a> <FONT color="green">512</FONT> * Creates and initializes a default generator if null.<a name="line.512"></a> <FONT color="green">513</FONT> * </p><a name="line.513"></a> <FONT color="green">514</FONT> *<a name="line.514"></a> <FONT color="green">515</FONT> * @return the Random used to generate random data<a name="line.515"></a> <FONT color="green">516</FONT> * @since 1.1<a name="line.516"></a> <FONT color="green">517</FONT> */<a name="line.517"></a> <FONT color="green">518</FONT> private RandomGenerator getRan() {<a name="line.518"></a> <FONT color="green">519</FONT> if (rand == null) {<a name="line.519"></a> <FONT color="green">520</FONT> rand = new JDKRandomGenerator();<a name="line.520"></a> <FONT color="green">521</FONT> rand.setSeed(System.currentTimeMillis());<a name="line.521"></a> <FONT color="green">522</FONT> }<a name="line.522"></a> <FONT color="green">523</FONT> return rand;<a name="line.523"></a> <FONT color="green">524</FONT> }<a name="line.524"></a> <FONT color="green">525</FONT> <a name="line.525"></a> <FONT color="green">526</FONT> /**<a name="line.526"></a> <FONT color="green">527</FONT> * Returns the SecureRandom used to generate secure random data.<a name="line.527"></a> <FONT color="green">528</FONT> * <p><a name="line.528"></a> <FONT color="green">529</FONT> * Creates and initializes if null.<a name="line.529"></a> <FONT color="green">530</FONT> * </p><a name="line.530"></a> <FONT color="green">531</FONT> *<a name="line.531"></a> <FONT color="green">532</FONT> * @return the SecureRandom used to generate secure random data<a name="line.532"></a> <FONT color="green">533</FONT> */<a name="line.533"></a> <FONT color="green">534</FONT> private SecureRandom getSecRan() {<a name="line.534"></a> <FONT color="green">535</FONT> if (secRand == null) {<a name="line.535"></a> <FONT color="green">536</FONT> secRand = new SecureRandom();<a name="line.536"></a> <FONT color="green">537</FONT> secRand.setSeed(System.currentTimeMillis());<a name="line.537"></a> <FONT color="green">538</FONT> }<a name="line.538"></a> <FONT color="green">539</FONT> return secRand;<a name="line.539"></a> <FONT color="green">540</FONT> }<a name="line.540"></a> <FONT color="green">541</FONT> <a name="line.541"></a> <FONT color="green">542</FONT> /**<a name="line.542"></a> <FONT color="green">543</FONT> * Reseeds the random number generator with the supplied seed.<a name="line.543"></a> <FONT color="green">544</FONT> * <p><a name="line.544"></a> <FONT color="green">545</FONT> * Will create and initialize if null.<a name="line.545"></a> <FONT color="green">546</FONT> * </p><a name="line.546"></a> <FONT color="green">547</FONT> *<a name="line.547"></a> <FONT color="green">548</FONT> * @param seed<a name="line.548"></a> <FONT color="green">549</FONT> * the seed value to use<a name="line.549"></a> <FONT color="green">550</FONT> */<a name="line.550"></a> <FONT color="green">551</FONT> public void reSeed(long seed) {<a name="line.551"></a> <FONT color="green">552</FONT> if (rand == null) {<a name="line.552"></a> <FONT color="green">553</FONT> rand = new JDKRandomGenerator();<a name="line.553"></a> <FONT color="green">554</FONT> }<a name="line.554"></a> <FONT color="green">555</FONT> rand.setSeed(seed);<a name="line.555"></a> <FONT color="green">556</FONT> }<a name="line.556"></a> <FONT color="green">557</FONT> <a name="line.557"></a> <FONT color="green">558</FONT> /**<a name="line.558"></a> <FONT color="green">559</FONT> * Reseeds the secure random number generator with the current time in<a name="line.559"></a> <FONT color="green">560</FONT> * milliseconds.<a name="line.560"></a> <FONT color="green">561</FONT> * <p><a name="line.561"></a> <FONT color="green">562</FONT> * Will create and initialize if null.<a name="line.562"></a> <FONT color="green">563</FONT> * </p><a name="line.563"></a> <FONT color="green">564</FONT> */<a name="line.564"></a> <FONT color="green">565</FONT> public void reSeedSecure() {<a name="line.565"></a> <FONT color="green">566</FONT> if (secRand == null) {<a name="line.566"></a> <FONT color="green">567</FONT> secRand = new SecureRandom();<a name="line.567"></a> <FONT color="green">568</FONT> }<a name="line.568"></a> <FONT color="green">569</FONT> secRand.setSeed(System.currentTimeMillis());<a name="line.569"></a> <FONT color="green">570</FONT> }<a name="line.570"></a> <FONT color="green">571</FONT> <a name="line.571"></a> <FONT color="green">572</FONT> /**<a name="line.572"></a> <FONT color="green">573</FONT> * Reseeds the secure random number generator with the supplied seed.<a name="line.573"></a> <FONT color="green">574</FONT> * <p><a name="line.574"></a> <FONT color="green">575</FONT> * Will create and initialize if null.<a name="line.575"></a> <FONT color="green">576</FONT> * </p><a name="line.576"></a> <FONT color="green">577</FONT> *<a name="line.577"></a> <FONT color="green">578</FONT> * @param seed<a name="line.578"></a> <FONT color="green">579</FONT> * the seed value to use<a name="line.579"></a> <FONT color="green">580</FONT> */<a name="line.580"></a> <FONT color="green">581</FONT> public void reSeedSecure(long seed) {<a name="line.581"></a> <FONT color="green">582</FONT> if (secRand == null) {<a name="line.582"></a> <FONT color="green">583</FONT> secRand = new SecureRandom();<a name="line.583"></a> <FONT color="green">584</FONT> }<a name="line.584"></a> <FONT color="green">585</FONT> secRand.setSeed(seed);<a name="line.585"></a> <FONT color="green">586</FONT> }<a name="line.586"></a> <FONT color="green">587</FONT> <a name="line.587"></a> <FONT color="green">588</FONT> /**<a name="line.588"></a> <FONT color="green">589</FONT> * Reseeds the random number generator with the current time in<a name="line.589"></a> <FONT color="green">590</FONT> * milliseconds.<a name="line.590"></a> <FONT color="green">591</FONT> */<a name="line.591"></a> <FONT color="green">592</FONT> public void reSeed() {<a name="line.592"></a> <FONT color="green">593</FONT> if (rand == null) {<a name="line.593"></a> <FONT color="green">594</FONT> rand = new JDKRandomGenerator();<a name="line.594"></a> <FONT color="green">595</FONT> }<a name="line.595"></a> <FONT color="green">596</FONT> rand.setSeed(System.currentTimeMillis());<a name="line.596"></a> <FONT color="green">597</FONT> }<a name="line.597"></a> <FONT color="green">598</FONT> <a name="line.598"></a> <FONT color="green">599</FONT> /**<a name="line.599"></a> <FONT color="green">600</FONT> * Sets the PRNG algorithm for the underlying SecureRandom instance using<a name="line.600"></a> <FONT color="green">601</FONT> * the Security Provider API. The Security Provider API is defined in <a<a name="line.601"></a> <FONT color="green">602</FONT> * href =<a name="line.602"></a> <FONT color="green">603</FONT> * "http://java.sun.com/j2se/1.3/docs/guide/security/CryptoSpec.html#AppA"><a name="line.603"></a> <FONT color="green">604</FONT> * Java Cryptography Architecture API Specification & Reference.</a><a name="line.604"></a> <FONT color="green">605</FONT> * <p><a name="line.605"></a> <FONT color="green">606</FONT> * <strong>USAGE NOTE:</strong> This method carries <i>significant</i><a name="line.606"></a> <FONT color="green">607</FONT> * overhead and may take several seconds to execute.<a name="line.607"></a> <FONT color="green">608</FONT> * </p><a name="line.608"></a> <FONT color="green">609</FONT> *<a name="line.609"></a> <FONT color="green">610</FONT> * @param algorithm<a name="line.610"></a> <FONT color="green">611</FONT> * the name of the PRNG algorithm<a name="line.611"></a> <FONT color="green">612</FONT> * @param provider<a name="line.612"></a> <FONT color="green">613</FONT> * the name of the provider<a name="line.613"></a> <FONT color="green">614</FONT> * @throws NoSuchAlgorithmException<a name="line.614"></a> <FONT color="green">615</FONT> * if the specified algorithm is not available<a name="line.615"></a> <FONT color="green">616</FONT> * @throws NoSuchProviderException<a name="line.616"></a> <FONT color="green">617</FONT> * if the specified provider is not installed<a name="line.617"></a> <FONT color="green">618</FONT> */<a name="line.618"></a> <FONT color="green">619</FONT> public void setSecureAlgorithm(String algorithm, String provider)<a name="line.619"></a> <FONT color="green">620</FONT> throws NoSuchAlgorithmException, NoSuchProviderException {<a name="line.620"></a> <FONT color="green">621</FONT> secRand = SecureRandom.getInstance(algorithm, provider);<a name="line.621"></a> <FONT color="green">622</FONT> }<a name="line.622"></a> <FONT color="green">623</FONT> <a name="line.623"></a> <FONT color="green">624</FONT> /**<a name="line.624"></a> <FONT color="green">625</FONT> * Generates an integer array of length <code>k</code> whose entries are<a name="line.625"></a> <FONT color="green">626</FONT> * selected randomly, without repetition, from the integers<a name="line.626"></a> <FONT color="green">627</FONT> * <code>0 through n-1</code> (inclusive).<a name="line.627"></a> <FONT color="green">628</FONT> * <p><a name="line.628"></a> <FONT color="green">629</FONT> * Generated arrays represent permutations of <code>n</code> taken<a name="line.629"></a> <FONT color="green">630</FONT> * <code>k</code> at a time.<a name="line.630"></a> <FONT color="green">631</FONT> * </p><a name="line.631"></a> <FONT color="green">632</FONT> * <p><a name="line.632"></a> <FONT color="green">633</FONT> * <strong>Preconditions:</strong><a name="line.633"></a> <FONT color="green">634</FONT> * <ul><a name="line.634"></a> <FONT color="green">635</FONT> * <li> <code>k <= n</code></li><a name="line.635"></a> <FONT color="green">636</FONT> * <li> <code>n > 0</code></li><a name="line.636"></a> <FONT color="green">637</FONT> * </ul><a name="line.637"></a> <FONT color="green">638</FONT> * If the preconditions are not met, an IllegalArgumentException is thrown.<a name="line.638"></a> <FONT color="green">639</FONT> * </p><a name="line.639"></a> <FONT color="green">640</FONT> * <p><a name="line.640"></a> <FONT color="green">641</FONT> * Uses a 2-cycle permutation shuffle. The shuffling process is described <a<a name="line.641"></a> <FONT color="green">642</FONT> * href="http://www.maths.abdn.ac.uk/~igc/tch/mx4002/notes/node83.html"><a name="line.642"></a> <FONT color="green">643</FONT> * here</a>.<a name="line.643"></a> <FONT color="green">644</FONT> * </p><a name="line.644"></a> <FONT color="green">645</FONT> *<a name="line.645"></a> <FONT color="green">646</FONT> * @param n<a name="line.646"></a> <FONT color="green">647</FONT> * domain of the permutation (must be positive)<a name="line.647"></a> <FONT color="green">648</FONT> * @param k<a name="line.648"></a> <FONT color="green">649</FONT> * size of the permutation (must satisfy 0 < k <= n).<a name="line.649"></a> <FONT color="green">650</FONT> * @return the random permutation as an int array<a name="line.650"></a> <FONT color="green">651</FONT> */<a name="line.651"></a> <FONT color="green">652</FONT> public int[] nextPermutation(int n, int k) {<a name="line.652"></a> <FONT color="green">653</FONT> if (k > n) {<a name="line.653"></a> <FONT color="green">654</FONT> throw MathRuntimeException.createIllegalArgumentException(<a name="line.654"></a> <FONT color="green">655</FONT> "permutation k ({0}) exceeds n ({1})", k, n);<a name="line.655"></a> <FONT color="green">656</FONT> }<a name="line.656"></a> <FONT color="green">657</FONT> if (k == 0) {<a name="line.657"></a> <FONT color="green">658</FONT> throw MathRuntimeException.createIllegalArgumentException(<a name="line.658"></a> <FONT color="green">659</FONT> "permutation k ({0}) must be positive", k);<a name="line.659"></a> <FONT color="green">660</FONT> }<a name="line.660"></a> <FONT color="green">661</FONT> <a name="line.661"></a> <FONT color="green">662</FONT> int[] index = getNatural(n);<a name="line.662"></a> <FONT color="green">663</FONT> shuffle(index, n - k);<a name="line.663"></a> <FONT color="green">664</FONT> int[] result = new int[k];<a name="line.664"></a> <FONT color="green">665</FONT> for (int i = 0; i < k; i++) {<a name="line.665"></a> <FONT color="green">666</FONT> result[i] = index[n - i - 1];<a name="line.666"></a> <FONT color="green">667</FONT> }<a name="line.667"></a> <FONT color="green">668</FONT> <a name="line.668"></a> <FONT color="green">669</FONT> return result;<a name="line.669"></a> <FONT color="green">670</FONT> }<a name="line.670"></a> <FONT color="green">671</FONT> <a name="line.671"></a> <FONT color="green">672</FONT> /**<a name="line.672"></a> <FONT color="green">673</FONT> * Uses a 2-cycle permutation shuffle to generate a random permutation.<a name="line.673"></a> <FONT color="green">674</FONT> * <strong>Algorithm Description</strong>: Uses a 2-cycle permutation<a name="line.674"></a> <FONT color="green">675</FONT> * shuffle to generate a random permutation of <code>c.size()</code> and<a name="line.675"></a> <FONT color="green">676</FONT> * then returns the elements whose indexes correspond to the elements of the<a name="line.676"></a> <FONT color="green">677</FONT> * generated permutation. This technique is described, and proven to<a name="line.677"></a> <FONT color="green">678</FONT> * generate random samples, <a<a name="line.678"></a> <FONT color="green">679</FONT> * href="http://www.maths.abdn.ac.uk/~igc/tch/mx4002/notes/node83.html"><a name="line.679"></a> <FONT color="green">680</FONT> * here</a><a name="line.680"></a> <FONT color="green">681</FONT> *<a name="line.681"></a> <FONT color="green">682</FONT> * @param c<a name="line.682"></a> <FONT color="green">683</FONT> * Collection to sample from.<a name="line.683"></a> <FONT color="green">684</FONT> * @param k<a name="line.684"></a> <FONT color="green">685</FONT> * sample size.<a name="line.685"></a> <FONT color="green">686</FONT> * @return the random sample.<a name="line.686"></a> <FONT color="green">687</FONT> */<a name="line.687"></a> <FONT color="green">688</FONT> public Object[] nextSample(Collection<?> c, int k) {<a name="line.688"></a> <FONT color="green">689</FONT> int len = c.size();<a name="line.689"></a> <FONT color="green">690</FONT> if (k > len) {<a name="line.690"></a> <FONT color="green">691</FONT> throw MathRuntimeException.createIllegalArgumentException(<a name="line.691"></a> <FONT color="green">692</FONT> "sample size ({0}) exceeds collection size ({1})");<a name="line.692"></a> <FONT color="green">693</FONT> }<a name="line.693"></a> <FONT color="green">694</FONT> if (k <= 0) {<a name="line.694"></a> <FONT color="green">695</FONT> throw MathRuntimeException.createIllegalArgumentException(<a name="line.695"></a> <FONT color="green">696</FONT> "sample size must be positive ({0})", k);<a name="line.696"></a> <FONT color="green">697</FONT> }<a name="line.697"></a> <FONT color="green">698</FONT> <a name="line.698"></a> <FONT color="green">699</FONT> Object[] objects = c.toArray();<a name="line.699"></a> <FONT color="green">700</FONT> int[] index = nextPermutation(len, k);<a name="line.700"></a> <FONT color="green">701</FONT> Object[] result = new Object[k];<a name="line.701"></a> <FONT color="green">702</FONT> for (int i = 0; i < k; i++) {<a name="line.702"></a> <FONT color="green">703</FONT> result[i] = objects[index[i]];<a name="line.703"></a> <FONT color="green">704</FONT> }<a name="line.704"></a> <FONT color="green">705</FONT> return result;<a name="line.705"></a> <FONT color="green">706</FONT> }<a name="line.706"></a> <FONT color="green">707</FONT> <a name="line.707"></a> <FONT color="green">708</FONT> // ------------------------Private methods----------------------------------<a name="line.708"></a> <FONT color="green">709</FONT> <a name="line.709"></a> <FONT color="green">710</FONT> /**<a name="line.710"></a> <FONT color="green">711</FONT> * Uses a 2-cycle permutation shuffle to randomly re-order the last elements<a name="line.711"></a> <FONT color="green">712</FONT> * of list.<a name="line.712"></a> <FONT color="green">713</FONT> *<a name="line.713"></a> <FONT color="green">714</FONT> * @param list<a name="line.714"></a> <FONT color="green">715</FONT> * list to be shuffled<a name="line.715"></a> <FONT color="green">716</FONT> * @param end<a name="line.716"></a> <FONT color="green">717</FONT> * element past which shuffling begins<a name="line.717"></a> <FONT color="green">718</FONT> */<a name="line.718"></a> <FONT color="green">719</FONT> private void shuffle(int[] list, int end) {<a name="line.719"></a> <FONT color="green">720</FONT> int target = 0;<a name="line.720"></a> <FONT color="green">721</FONT> for (int i = list.length - 1; i >= end; i--) {<a name="line.721"></a> <FONT color="green">722</FONT> if (i == 0) {<a name="line.722"></a> <FONT color="green">723</FONT> target = 0;<a name="line.723"></a> <FONT color="green">724</FONT> } else {<a name="line.724"></a> <FONT color="green">725</FONT> target = nextInt(0, i);<a name="line.725"></a> <FONT color="green">726</FONT> }<a name="line.726"></a> <FONT color="green">727</FONT> int temp = list[target];<a name="line.727"></a> <FONT color="green">728</FONT> list[target] = list[i];<a name="line.728"></a> <FONT color="green">729</FONT> list[i] = temp;<a name="line.729"></a> <FONT color="green">730</FONT> }<a name="line.730"></a> <FONT color="green">731</FONT> }<a name="line.731"></a> <FONT color="green">732</FONT> <a name="line.732"></a> <FONT color="green">733</FONT> /**<a name="line.733"></a> <FONT color="green">734</FONT> * Returns an array representing n.<a name="line.734"></a> <FONT color="green">735</FONT> *<a name="line.735"></a> <FONT color="green">736</FONT> * @param n<a name="line.736"></a> <FONT color="green">737</FONT> * the natural number to represent<a name="line.737"></a> <FONT color="green">738</FONT> * @return array with entries = elements of n<a name="line.738"></a> <FONT color="green">739</FONT> */<a name="line.739"></a> <FONT color="green">740</FONT> private int[] getNatural(int n) {<a name="line.740"></a> <FONT color="green">741</FONT> int[] natural = new int[n];<a name="line.741"></a> <FONT color="green">742</FONT> for (int i = 0; i < n; i++) {<a name="line.742"></a> <FONT color="green">743</FONT> natural[i] = i;<a name="line.743"></a> <FONT color="green">744</FONT> }<a name="line.744"></a> <FONT color="green">745</FONT> return natural;<a name="line.745"></a> <FONT color="green">746</FONT> }<a name="line.746"></a> <FONT color="green">747</FONT> <a name="line.747"></a> <FONT color="green">748</FONT> }<a name="line.748"></a> </PRE> </BODY> </HTML>