Initial check in of big integer library

third_party/bigint/sample.cc

Index: third_party/bigint/sample.cc
diff --git a/third_party/bigint/sample.cc b/third_party/bigint/sample.cc
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+// Sample program demonstrating the use of the Big Integer Library.
+
+// Standard libraries
+#include <string>
+#include <iostream>
+
+// `BigIntegerLibrary.hh' includes all of the library headers.
+#include "BigIntegerLibrary.hh"
+
+int main() {
+	/* The library throws `const char *' error messages when things go
+	 * wrong.  It's a good idea to catch them using a `try' block like this
+	 * one.  Your C++ compiler might need a command-line option to compile
+	 * code that uses exceptions. */
+	try {
+		BigInteger a; // a is 0
+		int b = 535;
+
+		/* Any primitive integer can be converted implicitly to a
+		 * BigInteger. */
+		a = b;
+
+		/* The reverse conversion requires a method call (implicit
+		 * conversions were previously supported but caused trouble).
+		 * If a were too big for an int, the library would throw an
+		 * exception. */
+		b = a.toInt();
+
+		BigInteger c(a); // Copy a BigInteger.
+
+		// The int literal is converted to a BigInteger.
+		BigInteger d(-314159265);
+
+		/* This won't compile (at least on 32-bit machines) because the
+		 * number is too big to be a primitive integer literal, and
+		 * there's no such thing as a BigInteger literal. */
+		//BigInteger e(3141592653589793238462643383279);
+
+		// Instead you can convert the number from a string.
+		std::string s("3141592653589793238462643383279");
+		BigInteger f = stringToBigInteger(s);
+
+		// You can convert the other way too.
+		std::string s2 = bigIntegerToString(f); 
+
+		// f is implicitly stringified and sent to std::cout.
+		std::cout << f << std::endl;
+
+		/* Let's do some math!  The library overloads most of the
+		 * mathematical operators (including assignment operators) to
+		 * work on BigIntegers.  There are also ``copy-less''
+		 * operations; see `BigUnsigned.hh' for details. */
+
+		// Arithmetic operators
+		BigInteger g(314159), h(265);
+		std::cout << (g + h) << '\n'
+			<< (g - h) << '\n'
+			<< (g * h) << '\n'
+			<< (g / h) << '\n'
+			<< (g % h) << std::endl;
+
+		// Bitwise operators
+		BigUnsigned i(0xFF0000FF), j(0x0000FFFF);
+		// The library's << operator recognizes base flags.
+		std::cout.flags(std::ios::hex | std::ios::showbase);
+		std::cout << (i & j) << '\n'
+			<< (i | j) << '\n'
+			<< (i ^ j) << '\n'
+			// Shift distances are ordinary unsigned ints.
+			<< (j << 21) << '\n'
+			<< (j >> 10) << '\n';
+		std::cout.flags(std::ios::dec);
+
+		// Let's do some heavy lifting and calculate powers of 314.
+		int maxPower = 10;
+		BigUnsigned x(1), big314(314);
+		for (int power = 0; power <= maxPower; power++) {
+			std::cout << "314^" << power << " = " << x << std::endl;
+			x *= big314; // A BigInteger assignment operator
+		}
+
+		// Some big-integer algorithms (albeit on small integers).
+		std::cout << gcd(BigUnsigned(60), 72) << '\n'
+			<< modinv(BigUnsigned(7), 11) << '\n'
+			<< modexp(BigUnsigned(314), 159, 2653) << std::endl;
+
+		// Add your own code here to experiment with the library.
+	} catch(char const* err) {
+		std::cout << "The library threw an exception:\n"
+			<< err << std::endl;
+	}
+
+	return 0;
+}
+
+/*
+The original sample program produces this output:
+
+3141592653589793238462643383279
+314424
+313894
+83252135
+1185
+134
+0xFF
+0xFF00FFFF
+0xFF00FF00
+0x1FFFE00000
+0x3F
+314^0 = 1
+314^1 = 314
+314^2 = 98596
+314^3 = 30959144
+314^4 = 9721171216
+314^5 = 3052447761824
+314^6 = 958468597212736
+314^7 = 300959139524799104
+314^8 = 94501169810786918656
+314^9 = 29673367320587092457984
+314^10 = 9317437338664347031806976
+12
+8
+1931
+
+*/