Initial check in of big integer library

third_party/bigint/BigUnsignedInABase.cc

+#include "BigUnsignedInABase.hh"
+
+BigUnsignedInABase::BigUnsignedInABase(const Digit *d, Index l, Base base)
+        : NumberlikeArray<Digit>(d, l), base(base) {
+        // Check the base
+        if (base < 2)
+                throw "BigUnsignedInABase::BigUnsignedInABase(const Digit *, Index, Base): The base must be at least 2";
+
+        // Validate the digits.
+        for (Index i = 0; i < l; i++)
+                if (blk[i] >= base)
+                        throw "BigUnsignedInABase::BigUnsignedInABase(const Digit *, Index, Base): A digit is too large for the specified base";
+
+        // Eliminate any leading zeros we may have been passed.
+        zapLeadingZeros();
+}
+
+namespace {
+        unsigned int bitLen(unsigned int x) {
+                unsigned int len = 0;
+                while (x > 0) {
+                        x >>= 1;
+                        len++;
+                }
+                return len;
+        }
+        unsigned int ceilingDiv(unsigned int a, unsigned int b) {
+                return (a + b - 1) / b;
+        }
+}
+
+BigUnsignedInABase::BigUnsignedInABase(const BigUnsigned &x, Base base) {
+        // Check the base
+        if (base < 2)
+                throw "BigUnsignedInABase(BigUnsigned, Base): The base must be at least 2";
+        this->base = base;
+
+        // Get an upper bound on how much space we need
+        int maxBitLenOfX = x.getLength() * BigUnsigned::N;
+        int minBitsPerDigit = bitLen(base) - 1;
+        int maxDigitLenOfX = ceilingDiv(maxBitLenOfX, minBitsPerDigit);
+        len = maxDigitLenOfX; // Another change to comply with `staying in bounds'.
+        allocate(len); // Get the space
+
+        BigUnsigned x2(x), buBase(base);
+        Index digitNum = 0;
+
+        while (!x2.isZero()) {
+                // Get last digit.  This is like `lastDigit = x2 % buBase, x2 /= buBase'.
+                BigUnsigned lastDigit(x2);
+                lastDigit.divideWithRemainder(buBase, x2);
+                // Save the digit.
+                blk[digitNum] = lastDigit.toUnsignedShort();
+                // Move on.  We can't run out of room: we figured it out above.
+                digitNum++;
+        }
+
+        // Save the actual length.
+        len = digitNum;
+}
+
+BigUnsignedInABase::operator BigUnsigned() const {
+        BigUnsigned ans(0), buBase(base), temp;
+        Index digitNum = len;
+        while (digitNum > 0) {
+                digitNum--;
+                temp.multiply(ans, buBase);
+                ans.add(temp, BigUnsigned(blk[digitNum]));
+        }
+        return ans;
+}
+
+BigUnsignedInABase::BigUnsignedInABase(const std::string &s, Base base) {
+        // Check the base.
+        if (base > 36)
+                throw "BigUnsignedInABase(std::string, Base): The default string conversion routines use the symbol set 0-9, A-Z and therefore support only up to base 36.  You tried a conversion with a base over 36; write your own string conversion routine.";
+        // Save the base.
+        // This pattern is seldom seen in C++, but the analogous ``this.'' is common in Java.
+        this->base = base;
+
+        // `s.length()' is a `size_t', while `len' is a `NumberlikeArray::Index',
+        // also known as an `unsigned int'.  Some compilers warn without this cast.
+        len = Index(s.length());
+        allocate(len);
+
+        Index digitNum, symbolNumInString;
+        for (digitNum = 0; digitNum < len; digitNum++) {
+                symbolNumInString = len - 1 - digitNum;
+                char theSymbol = s[symbolNumInString];
+                if (theSymbol >= '0' && theSymbol <= '9')
+                        blk[digitNum] = theSymbol - '0';
+                else if (theSymbol >= 'A' && theSymbol <= 'Z')
+                        blk[digitNum] = theSymbol - 'A' + 10;
+                else if (theSymbol >= 'a' && theSymbol <= 'z')
+                        blk[digitNum] = theSymbol - 'a' + 10;
+                else
+                        throw "BigUnsignedInABase(std::string, Base): Bad symbol in input.  Only 0-9, A-Z, a-z are accepted.";
+
+                if (blk[digitNum] >= base)
+                        throw "BigUnsignedInABase::BigUnsignedInABase(const Digit *, Index, Base): A digit is too large for the specified base";
+        }
+        zapLeadingZeros();
+}
+
+BigUnsignedInABase::operator std::string() const {
+        if (base > 36)
+                throw "BigUnsignedInABase ==> std::string: The default string conversion routines use the symbol set 0-9, A-Z and therefore support only up to base 36.  You tried a conversion with a base over 36; write your own string conversion routine.";
+        if (len == 0)
+                return std::string("0");
+        // Some compilers don't have push_back, so use a char * buffer instead.
+        char *s = new char[len + 1];
+        s[len] = '\0';
+        Index digitNum, symbolNumInString;
+        for (symbolNumInString = 0; symbolNumInString < len; symbolNumInString++) {
+                digitNum = len - 1 - symbolNumInString;
+                Digit theDigit = blk[digitNum];
+                if (theDigit < 10)
+                        s[symbolNumInString] = char('0' + theDigit);
+                else
+                        s[symbolNumInString] = char('A' + theDigit - 10);
+        }
+        std::string s2(s);
+        delete [] s;
+        return s2;
+}