Squashed 'third_party/boostorg/units/' content from commit 57389b7
Change-Id: Id8ff79c1508f6103e20808f7a038f6a30d113b08
git-subtree-dir: third_party/boostorg/units
git-subtree-split: 57389b7374a6f7a4caf87cc44092bb8d0db65ec6
diff --git a/example/information.cpp b/example/information.cpp
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+// Boost.Units - A C++ library for zero-overhead dimensional analysis and
+// unit/quantity manipulation and conversion
+//
+// Copyright (C) 2014 Erik Erlandson
+//
+// Distributed under the Boost Software License, Version 1.0. (See
+// accompanying file LICENSE_1_0.txt or copy at
+// http://www.boost.org/LICENSE_1_0.txt)
+
+//#include <boost/units/systems/information.hpp>
+
+/**
+\file
+
+\brief information.cpp
+
+\details
+Demonstrate information unit system.
+
+Output:
+@verbatim
+bytes= 1.25e+08 B
+bits= 8e+06 b
+nats= 4605.17 nat
+1024 bytes in a kibi-byte
+8.38861e+06 bits in a mebi-byte
+0.000434294 hartleys in a milli-nat
+entropy in bits= 1 b
+entropy in nats= 0.693147 nat
+entropy in hartleys= 0.30103 Hart
+entropy in shannons= 1 Sh
+entropy in bytes= 0.125 B
+@endverbatim
+**/
+
+#include <cmath>
+#include <iostream>
+using std::cout;
+using std::endl;
+using std::log;
+
+#include <boost/units/quantity.hpp>
+#include <boost/units/io.hpp>
+#include <boost/units/conversion.hpp>
+namespace bu = boost::units;
+using bu::quantity;
+using bu::conversion_factor;
+
+// SI prefixes
+#include <boost/units/systems/si/prefixes.hpp>
+namespace si = boost::units::si;
+
+// information unit system
+#include <boost/units/systems/information.hpp>
+using namespace bu::information;
+
+// Define a function for the entropy of a bernoulli trial.
+// The formula is computed using natural log, so the units are in nats.
+// The user provides the desired return unit, the only restriction being that it
+// must be a unit of information. Conversion to the requested return unit is
+// accomplished automatically by the boost::units library.
+template <typename Sys>
+constexpr
+quantity<bu::unit<bu::information_dimension, Sys> >
+bernoulli_entropy(double p, const bu::unit<bu::information_dimension, Sys>&) {
+ typedef bu::unit<bu::information_dimension, Sys> requested_unit;
+ return quantity<requested_unit>((-(p*log(p) + (1-p)*log(1-p)))*nats);
+}
+
+int main(int argc, char** argv) {
+ // a quantity of information (default in units of bytes)
+ quantity<info> nbytes(1 * si::giga * bit);
+ cout << "bytes= " << nbytes << endl;
+
+ // a quantity of information, stored as bits
+ quantity<hu::bit::info> nbits(1 * si::mega * byte);
+ cout << "bits= " << nbits << endl;
+
+ // a quantity of information, stored as nats
+ quantity<hu::nat::info> nnats(2 * si::kilo * hartleys);
+ cout << "nats= " << nnats << endl;
+
+ // how many bytes are in a kibi-byte?
+ cout << conversion_factor(kibi * byte, byte) << " bytes in a kibi-byte" << endl;
+
+ // how many bits are in a mebi-byte?
+ cout << conversion_factor(mebi * byte, bit) << " bits in a mebi-byte" << endl;
+
+ // how many hartleys are in a milli-nat?
+ cout << conversion_factor(si::milli * nat, hartley) << " hartleys in a milli-nat" << endl;
+
+ // compute the entropy of a fair coin flip, in various units of information:
+ cout << "entropy in bits= " << bernoulli_entropy(0.5, bits) << endl;
+ cout << "entropy in nats= " << bernoulli_entropy(0.5, nats) << endl;
+ cout << "entropy in hartleys= " << bernoulli_entropy(0.5, hartleys) << endl;
+ cout << "entropy in shannons= " << bernoulli_entropy(0.5, shannons) << endl;
+ cout << "entropy in bytes= " << bernoulli_entropy(0.5, bytes) << endl;
+
+ return 0;
+}