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Diffstat (limited to 'libs/bigint/BigUnsignedInABase.hh')

-rw-r--r-- | libs/bigint/BigUnsignedInABase.hh | 122 |

1 files changed, 122 insertions, 0 deletions

diff --git a/libs/bigint/BigUnsignedInABase.hh b/libs/bigint/BigUnsignedInABase.hh new file mode 100644 index 00000000..0ea89c6e --- /dev/null +++ b/libs/bigint/BigUnsignedInABase.hh @@ -0,0 +1,122 @@ +#ifndef BIGUNSIGNEDINABASE_H +#define BIGUNSIGNEDINABASE_H + +#include "NumberlikeArray.hh" +#include "BigUnsigned.hh" +#include <string> + +/* + * A BigUnsignedInABase object represents a nonnegative integer of size limited + * only by available memory, represented in a user-specified base that can fit + * in an `unsigned short' (most can, and this saves memory). + * + * BigUnsignedInABase is intended as an intermediary class with little + * functionality of its own. BigUnsignedInABase objects can be constructed + * from, and converted to, BigUnsigneds (requiring multiplication, mods, etc.) + * and `std::string's (by switching digit values for appropriate characters). + * + * BigUnsignedInABase is similar to BigUnsigned. Note the following: + * + * (1) They represent the number in exactly the same way, except that + * BigUnsignedInABase uses ``digits'' (or Digit) where BigUnsigned uses + * ``blocks'' (or Blk). + * + * (2) Both use the management features of NumberlikeArray. (In fact, my desire + * to add a BigUnsignedInABase class without duplicating a lot of code led me to + * introduce NumberlikeArray.) + * + * (3) The only arithmetic operation supported by BigUnsignedInABase is an + * equality test. Use BigUnsigned for arithmetic. + */ + +class BigUnsignedInABase : protected NumberlikeArray<unsigned short> { + +public: + // The digits of a BigUnsignedInABase are unsigned shorts. + typedef unsigned short Digit; + // That's also the type of a base. + typedef Digit Base; + +protected: + // The base in which this BigUnsignedInABase is expressed + Base base; + + // Creates a BigUnsignedInABase with a capacity; for internal use. + BigUnsignedInABase(int, Index c) : NumberlikeArray<Digit>(0, c) {} + + // Decreases len to eliminate any leading zero digits. + void zapLeadingZeros() { + while (len > 0 && blk[len - 1] == 0) + len--; + } + +public: + // Constructs zero in base 2. + BigUnsignedInABase() : NumberlikeArray<Digit>(), base(2) {} + + // Copy constructor + BigUnsignedInABase(const BigUnsignedInABase &x) : NumberlikeArray<Digit>(x), base(x.base) {} + + // Assignment operator + void operator =(const BigUnsignedInABase &x) { + NumberlikeArray<Digit>::operator =(x); + base = x.base; + } + + // Constructor that copies from a given array of digits. + BigUnsignedInABase(const Digit *d, Index l, Base base); + + // Destructor. NumberlikeArray does the delete for us. + ~BigUnsignedInABase() {} + + // LINKS TO BIGUNSIGNED + BigUnsignedInABase(const BigUnsigned &x, Base base); + operator BigUnsigned() const; + + /* LINKS TO STRINGS + * + * These use the symbols ``0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ'' to + * represent digits of 0 through 35. When parsing strings, lowercase is + * also accepted. + * + * All string representations are big-endian (big-place-value digits + * first). (Computer scientists have adopted zero-based counting; why + * can't they tolerate little-endian numbers?) + * + * No string representation has a ``base indicator'' like ``0x''. + * + * An exception is made for zero: it is converted to ``0'' and not the + * empty string. + * + * If you want different conventions, write your own routines to go + * between BigUnsignedInABase and strings. It's not hard. + */ + operator std::string() const; + BigUnsignedInABase(const std::string &s, Base base); + +public: + + // ACCESSORS + Base getBase() const { return base; } + + // Expose these from NumberlikeArray directly. + using NumberlikeArray<Digit>::getCapacity; + using NumberlikeArray<Digit>::getLength; + + /* Returns the requested digit, or 0 if it is beyond the length (as if + * the number had 0s infinitely to the left). */ + Digit getDigit(Index i) const { return i >= len ? 0 : blk[i]; } + + // The number is zero if and only if the canonical length is zero. + bool isZero() const { return NumberlikeArray<Digit>::isEmpty(); } + + /* Equality test. For the purposes of this test, two BigUnsignedInABase + * values must have the same base to be equal. */ + bool operator ==(const BigUnsignedInABase &x) const { + return base == x.base && NumberlikeArray<Digit>::operator ==(x); + } + bool operator !=(const BigUnsignedInABase &x) const { return !operator ==(x); } + +}; + +#endif |