Old snapshot `BigIntegerLibrary-2005.01.16'; see the ChangeLog file.

[bigint/bigint.git] / BigUnsigned.hh

diff --git a/BigUnsigned.hh b/BigUnsigned.hh
index 72513af..2a55625 100644 (file)
--- a/BigUnsigned.hh
+++ b/BigUnsigned.hh
@@ -110,16 +110,51 @@ class BigUnsigned : protected NumberlikeArray<unsigned long> {
        bool operator <=(const BigUnsigned &x) const { return compareTo(x) != greater; }
        bool operator >=(const BigUnsigned &x) const { return compareTo(x) != less   ; }
        bool operator > (const BigUnsigned &x) const { return compareTo(x) == greater; }
+
+       /*
+       * BigUnsigned and BigInteger both provide three kinds of operators.
+       * Here ``big-integer'' refers to BigInteger or BigUnsigned.
+       *
+       * (1) Overloaded ``return-by-value'' operators:
+       *     +, -, *, /, %, unary -.
+       * Big-integer code using these operators looks identical to
+       * code using the primitive integer types.  These operators take
+       * one or two big-integer inputs and return a big-integer result,
+       * which can then be assigned to a BigInteger variable or used
+       * in an expression.  Example:
+       *     BigInteger a(1), b = 1;
+       *     BigInteger c = a + b;
+       *
+       * (2) Overloaded assignment operators:
+       *     +=, -=, *=, /=, %=, &=, |=, ^=, ++, --, flipSign.
+       * Again, these are used on big integers just like on ints.
+       * They take one writable big integer that both provides an
+       * operand and receives a result.  The first eight also take
+       * a second read-only operand.  Example:
+       *     BigInteger a(1), b(1);
+       *     a += b;
+       *
+       * (3) ``Put-here'' operations: `add', `subtract', etc.
+       * Using a return-by-value or assignment operator generally involves
+       * copy constructions and/or assignments.  The ``put-here'' operations
+       * require none, but they are more of a hassle to use.  Most take two
+       * read-only operands and save the result in the calling object `*this',
+       * whose previous value is ignored.  `divideWithRemainder' is an exception.
+       * <<< NOTE >>>: Put-here operations do not return a value: they don't need to!!
+       * Examples:
+       *     BigInteger a(43), b(7), c, d;
+       *     c = a + b;   // Now c == 50.
+       *     c.add(a, b); // Same effect but without the two bulk-copies.
+       *     c.divideWithRemainder(b, d); // 50 / 7; now d == 7 (quotient) and c == 1 (remainder).
+       *     a.add(a, b); // Unsafe ``aliased'' call; causes a runtime error.
+       */
        
        // PUT-HERE OPERATIONS
-       /* These store the result of the operation on the arguments into this.
-       * a.add(b, c) is equivalent to, but faster than, a = b + c.
-       * Calls like a.operation(a, b) are unsafe and not allowed. */
        public:
-       // Easy 3
-       void add          (const BigUnsigned &a, const BigUnsigned &b); // Addition
-       void subtract     (const BigUnsigned &a, const BigUnsigned &b); // Subtraction
-       void multiply     (const BigUnsigned &a, const BigUnsigned &b); // Multiplication
+       /* These 3: Two read-only operands as arguments.  Result left in *this. */
+       void add(const BigUnsigned &a, const BigUnsigned &b); // Addition
+       void subtract(const BigUnsigned &a, const BigUnsigned &b); // Subtraction
+       void multiply(const BigUnsigned &a, const BigUnsigned &b); // Multiplication
        /* Divisive stuff
        * `a.divideWithRemainder(b, q)' is like `q = a / b, a %= b'.
        * Semantics similar to Donald E. Knuth's are used for / and %,
@@ -129,28 +164,30 @@ class BigUnsigned : protected NumberlikeArray<unsigned long> {
        */
        void divideWithRemainder(const BigUnsigned &b, BigUnsigned &q);
        void divide(const BigUnsigned &a, const BigUnsigned &b) {
-               // Division, deprecated and provided for compatibility
+               // Division, deprecated and provided for backward compatibility
                BigUnsigned a2(a);
                a2.divideWithRemainder(b, *this);
                // quotient now in *this
                // don't care about remainder left in a2
        }
        void modulo(const BigUnsigned &a, const BigUnsigned &b) {
-               // Modular reduction, deprecated and provided for compatibility
+               // Modular reduction, deprecated and provided for backward compatibility
                *this = a;
                BigUnsigned q;
                divideWithRemainder(b, q);
                // remainder now in *this
                // don't care about quotient left in q
        }
-       // Bitwise
-       void bitAnd       (const BigUnsigned &a, const BigUnsigned &b); // Bitwise AND
-       void bitOr        (const BigUnsigned &a, const BigUnsigned &b); // Bitwise OR
-       void bitXor       (const BigUnsigned &a, const BigUnsigned &b); // Bitwise XOR
+       // Bitwise operations.  Two read-only operands as arguments.  Result left in *this.
+       // These are not provided for BigIntegers; I think that using them on BigIntegers
+       // will discard the sign first.
+       void bitAnd(const BigUnsigned &a, const BigUnsigned &b); // Bitwise AND
+       void bitOr(const BigUnsigned &a, const BigUnsigned &b); // Bitwise OR
+       void bitXor(const BigUnsigned &a, const BigUnsigned &b); // Bitwise XOR
        
        // These functions are declared but not defined.  (Sorry.)
        // Trying to call either will result in a link-time error.
-       void bitShiftLeft (const BigUnsigned &a, unsigned int b); // Bitwise left shift
+       void bitShiftLeft(const BigUnsigned &a, unsigned int b); // Bitwise left shift
        void bitShiftRight(const BigUnsigned &a, unsigned int b); // Bitwise right shift
        
        // NORMAL OPERATORS