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::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();
}
void BigUnsigned::subtract(const BigUnsigned &a, const BigUnsigned &b) {
DTRT_ALIASED(this == &a || this == &b, subtract(a, b));
if (b.len == 0) {
// If b is zero, copy a.
operator =(a);
return;
} else if (a.len < b.len)
// If a is shorter than b, the result is negative.
throw "BigUnsigned::subtract: "
"Negative result in unsigned calculation";
// Some variables...
bool borrowIn, borrowOut;
Blk temp;
Index i;
// Set preliminary length and make room
len = a.len;
allocate(len);
// For each block index that is present in both inputs...
for (i = 0, borrowIn = false; i < b.len; i++) {
temp = a.blk[i] - b.blk[i];
// If a reverse rollover occurred,
// the result is greater than the block from a.
borrowOut = (temp > a.blk[i]);
// Handle an incoming borrow
if (borrowIn) {
borrowOut |= (temp == 0);
temp--;
}
blk[i] = temp; // Save the subtraction result
borrowIn = borrowOut; // Pass the borrow along
}
// If there is a borrow left over, decrease blocks until
// one does not reverse rollover.
for (; i < a.len && borrowIn; i++) {
borrowIn = (a.blk[i] == 0);
blk[i] = a.blk[i] - 1;
}
/* If there's still a borrow, the result is negative.
* Throw an exception, but zero out this object so as to leave it in a
* predictable state. */
if (borrowIn) {
len = 0;
throw "BigUnsigned::subtract: Negative result in unsigned calculation";
} else
// Copy over the rest of the blocks
for (; i < a.len; i++)
blk[i] = a.blk[i];
// Zap leading zeros
zapLeadingZeros();
}
void BigUnsigned::setBlock(Index i, Blk newBlock) {
if (newBlock == 0) {
if (i < len) {
blk[i] = 0;
zapLeadingZeros();
}
// If i >= len, no effect.
} else {
if (i >= len) {
// The nonzero block extends the number.
allocateAndCopy(i+1);
// Zero any added blocks that we aren't setting.
for (Index j = len; j < i; j++)
blk[j] = 0;
len = i+1;
}
blk[i] = newBlock;
}
}
