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133 lines
3.8 KiB
C++
133 lines
3.8 KiB
C++
/*
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Apply various randomness tests to a stream of bytes
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by John Walker -- September 1996
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http://www.fourmilab.ch/random
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This software is in the public domain. Permission to use, copy, modify,
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and distribute this software and its documentation for any purpose and
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without fee is hereby granted, without any conditions or restrictions.
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This software is provided “as is” without express or implied warranty.
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Modified for Zeek/Bro by Seth Hall - July 2010
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*/
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#include "zeek/RandTest.h"
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#include <cmath>
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constexpr double log2of10 = 3.32192809488736234787;
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/* RT_LOG2 -- Calculate log to the base 2 */
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static double rt_log2(double x) { return log2of10 * log10(x); }
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// RT_INCIRC = pow(pow(256.0, (double) (RT_MONTEN / 2)) - 1, 2.0);
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constexpr double RT_INCIRC = 281474943156225.0;
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namespace zeek::detail {
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RandTest::RandTest() {
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totalc = 0;
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mp = 0;
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sccfirst = 1;
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inmont = mcount = 0;
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cexp = montex = montey = montepi = sccu0 = scclast = scct1 = scct2 = scct3 = 0.0;
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for ( int i = 0; i < 256; i++ ) {
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ccount[i] = 0;
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}
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}
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void RandTest::add(const void* buf, int bufl) {
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const unsigned char* bp = static_cast<const unsigned char*>(buf);
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int oc;
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while ( bufl-- > 0 ) {
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oc = *bp++;
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ccount[oc]++; /* Update counter for this bin */
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totalc++;
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/* Update inside / outside circle counts for Monte Carlo
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computation of PI */
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monte[mp++] = oc; /* Save character for Monte Carlo */
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if ( mp >= RT_MONTEN ) /* Calculate every RT_MONTEN character */
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{
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mp = 0;
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mcount++;
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montex = 0;
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montey = 0;
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for ( int mj = 0; mj < RT_MONTEN / 2; mj++ ) {
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montex = (montex * 256.0) + monte[mj];
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montey = (montey * 256.0) + monte[(RT_MONTEN / 2) + mj];
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}
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if ( montex * montex + montey * montey <= RT_INCIRC ) {
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inmont++;
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}
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}
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/* Update calculation of serial correlation coefficient */
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if ( sccfirst ) {
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sccfirst = 0;
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sccu0 = oc;
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}
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else {
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scct1 = scct1 + scclast * oc;
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}
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scct2 = scct2 + oc;
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scct3 = scct3 + (oc * oc);
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scclast = oc;
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oc <<= 1;
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}
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}
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void RandTest::end(double* r_ent, double* r_chisq, double* r_mean, double* r_montepicalc, double* r_scc) {
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int i;
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double ent = 0.0;
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double chisq = 0.0;
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double datasum = 0.0;
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double prob[256]; /* Probabilities per bin for entropy */
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/* Complete calculation of serial correlation coefficient */
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scct1 = scct1 + scclast * sccu0;
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scct2 = scct2 * scct2;
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double scc = totalc * scct3 - scct2;
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if ( scc == 0.0 )
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scc = -100000;
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else
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scc = (totalc * scct1 - scct2) / scc;
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/* Scan bins and calculate probability for each bin and
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Chi-Square distribution. The probability will be reused
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in the entropy calculation below. While we're at it,
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we sum of all the data which will be used to compute the
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mean. */
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cexp = totalc / 256.0; /* Expected count per bin */
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for ( i = 0; i < 256; i++ ) {
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double a = ccount[i] - cexp;
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prob[i] = ((double)ccount[i]) / totalc;
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chisq += (a * a) / cexp;
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datasum += ((double)i) * ccount[i];
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}
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/* Calculate entropy */
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for ( i = 0; i < 256; i++ ) {
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if ( prob[i] > 0.0 ) {
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ent += prob[i] * rt_log2(1 / prob[i]);
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}
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}
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/* Calculate Monte Carlo value for PI from percentage of hits
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within the circle */
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montepi = mcount == 0 ? 0 : 4.0 * (((double)inmont) / mcount);
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/* Return results through arguments */
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*r_ent = ent;
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*r_chisq = chisq;
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*r_mean = datasum / totalc;
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*r_montepicalc = montepi;
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*r_scc = scc;
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}
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} // namespace zeek::detail
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