/*
* Matt McCutchen's Big Integer Library
-* http://mysite.verizon.net/mccutchen/bigint/
*/
+/*
+* This mechanism prevents files from being included twice.
+* Each file gets its own `id' (here `NUMBERLIKEARRAY').
+* When `#include'd, this file checks whether its `id' has
+* already been flagged. If not, it flags the `id' and
+* loads the declarations.
+*/
#ifndef NUMBERLIKEARRAY
#define NUMBERLIKEARRAY
+// An essential memory-management constant.
+// I wish this were built into C++ just as it is in Java.
+#ifndef NULL
+#define NULL 0
+#endif
+
/*
-* A NumberlikeArray<Block> object holds a dynamically
-* allocated array of Blocks. It provides certain basic
+* A NumberlikeArray<Blk> object holds a dynamically
+* allocated array of Blk. It provides certain basic
* memory management features needed by both BigUnsigned
* and BigUnsignedInABase, which are both derived from it.
*
public:
typedef unsigned int Index; // Type for the index of a block in the array
+ static const unsigned int N; // The number of bits in a block, defined below.
// FIELDS
Index cap; // The current allocated capacity of this NumberlikeArray (in blocks)
Index len; // The actual length of the value stored in this NumberlikeArray (in blocks)
Blk *blk; // Dynamically allocated array of the blocks
+ /*
+ * Change made on 2005.01.06:
+ *
+ * If a zero-length NumberlikeArray is desired, no array is actually allocated.
+ * Instead, `blk' is set to `NULL', and `cap' and `len' are zero as usual.
+ *
+ * `blk' is never dereferenced if the array has zero length. Furthermore,
+ * `delete NULL;' does nothing and causes no error. Therefore, we can use
+ * `NULL' as if it were a zero-length array from `new'.
+ *
+ * This is a great convenience because the only code that need be changed
+ * is the array allocation code. All other code will still work fine.
+ */
+
// MANAGEMENT
- NumberlikeArray(int, Index c) : cap(c), len(0) { // Creates a NumberlikeArray with a capacity
- blk = new Blk[cap];
+ NumberlikeArray(Index c) : cap(c), len(0) { // Creates a NumberlikeArray with a capacity
+ blk = (cap > 0) ? (new Blk[cap]) : NULL;
}
void allocate(Index c); // Ensures the array has at least the indicated capacity, maybe discarding contents
void allocateAndCopy(Index c); // Ensures the array has at least the indicated capacity, preserving its contents
- NumberlikeArray() : cap(0), len(0) { // Default constructor (empty array)
- blk = new Blk[0];
+ /*
+ * Default constructor.
+ *
+ * If a class derived from NumberlikeArray knows at initializer time what size array
+ * it wants, it can call the first constructor listed above in an initializer.
+ *
+ * Otherwise, this default constructor will be implicitly invoked, pointing `blk' to
+ * `NULL', a fake zero-length block array. The derived class can allocate the desired
+ * array itself and overwrite `blk'; it need not `delete [] blk' first.
+ *
+ * This change fixes a memory leak reported by Milan Tomic on 2005.01.06.
+ * Integer-type-to-BigUnsigned (and BigInteger) conversion constructors have always
+ * allocated their own array of length 0 or 1 after seeing whether the input is zero.
+ * But when the NumberlikeArray transition occurred, these constructors contained an
+ * implicit initializer call to the old NumberlikeArray default constructor, which
+ * created a real `new'-allocated zero-length array. This array would then be lost,
+ * causing a small but annoying memory leak.
+ */
+ NumberlikeArray() : cap(0), len(0) {
+ blk = NULL;
}
NumberlikeArray(const NumberlikeArray<Blk> &x); // Copy constructor
void operator=(const NumberlikeArray<Blk> &x); // Assignment operator
NumberlikeArray(const Blk *b, Index l); // Constructor from an array of blocks
~NumberlikeArray() { // Destructor
- delete [] blk;
+ delete [] blk; // Does nothing and causes no error if `blk' is null.
}
// PICKING APART
// Derived classes may wish to override these if differing arrays can
// sometimes be considered equivalent.
bool operator ==(const NumberlikeArray<Blk> &x) const;
- bool operator !=(const NumberlikeArray<Blk> &x) const;
+ bool operator !=(const NumberlikeArray<Blk> &x) const { return !operator ==(x); }
};
/*
+* =================================
* BELOW THIS POINT are template definitions; above are declarations.
*
* Definitions would ordinarily belong in a file NumberlikeArray.cc so that they would
* so other files including NumberlikeArray will be able to generate real definitions.
*/
+template <class Blk>
+const unsigned int NumberlikeArray<Blk>::N = 8 * sizeof(Blk);
+
// MANAGEMENT
// This routine is called to ensure the array is at least a