Initial check in of big integer library

third_party/bigint/BigIntegerUtils.cc

+#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;
+}