Initial check in of big integer library

third_party/bigint/BigIntegerUtils.cc

Index: third_party/bigint/BigIntegerUtils.cc
diff --git a/third_party/bigint/BigIntegerUtils.cc b/third_party/bigint/BigIntegerUtils.cc
new file mode 100644
index 0000000000000000000000000000000000000000..44073af65274d3286a4c84d67fbd5aa287464962
--- /dev/null
+++ b/third_party/bigint/BigIntegerUtils.cc
@@ -0,0 +1,50 @@
+#include "BigIntegerUtils.hh"
+#include "BigUnsignedInABase.hh"
+
+std::string bigUnsignedToString(const BigUnsigned &x) {
+	return std::string(BigUnsignedInABase(x, 10));
+}
+
+std::string bigIntegerToString(const BigInteger &x) {
+	return (x.getSign() == BigInteger::negative)
+		? (std::string("-") + bigUnsignedToString(x.getMagnitude()))
+		: (bigUnsignedToString(x.getMagnitude()));
+}
+
+BigUnsigned stringToBigUnsigned(const std::string &s) {
+	return BigUnsigned(BigUnsignedInABase(s, 10));
+}
+
+BigInteger stringToBigInteger(const std::string &s) {
+	// Recognize a sign followed by a BigUnsigned.
+	return (s[0] == '-') ? BigInteger(stringToBigUnsigned(s.substr(1, s.length() - 1)), BigInteger::negative)
+		: (s[0] == '+') ? BigInteger(stringToBigUnsigned(s.substr(1, s.length() - 1)))
+		: BigInteger(stringToBigUnsigned(s));
+}
+
+std::ostream &operator <<(std::ostream &os, const BigUnsigned &x) {
+	BigUnsignedInABase::Base base;
+	long osFlags = os.flags();
+	if (osFlags & os.dec)
+		base = 10;
+	else if (osFlags & os.hex) {
+		base = 16;
+		if (osFlags & os.showbase)
+			os << "0x";
+	} else if (osFlags & os.oct) {
+		base = 8;
+		if (osFlags & os.showbase)
+			os << '0';
+	} else
+		throw "std::ostream << BigUnsigned: Could not determine the desired base from output-stream flags";
+	std::string s = std::string(BigUnsignedInABase(x, base));
+	os << s;
+	return os;
+}
+
+std::ostream &operator <<(std::ostream &os, const BigInteger &x) {
+	if (x.getSign() == BigInteger::negative)
+		os << '-';
+	os << x.getMagnitude();
+	return os;
+}