X-Git-Url: https://mattmccutchen.net/bigint/bigint.git/blobdiff_plain/05780f4b578d6ae054be0b19b8498d32a4f16c60..00c6448a6c5fc7a68427ca1dc3f5f523563e1041:/NumberlikeArray.hh

diff --git a/NumberlikeArray.hh b/NumberlikeArray.hh
index 10b7262..ab0aae0 100644
--- a/NumberlikeArray.hh
+++ b/NumberlikeArray.hh
@@ -1,14 +1,26 @@
 /*
 * 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.
 *
@@ -29,27 +41,60 @@ class NumberlikeArray {
 	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
@@ -63,11 +108,12 @@ class NumberlikeArray {
 	// 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
@@ -83,6 +129,9 @@ class NumberlikeArray {
 * 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