third_party/bigint/BigUnsignedInABase.hh

// Copyright 2014 The PDFium Authors
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

// Original code by Matt McCutchen, see the LICENSE file.

#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
	BigUnsignedInABase& operator =(const BigUnsignedInABase &x) {
		NumberlikeArray<Digit>::operator =(x);
		base = x.base;
		return *this;
	}

	// 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