Redo handling of aliased calls --> version 2007.02.13

[bigint/bigint.git] / BigInteger.cc

diff --git a/BigInteger.cc b/BigInteger.cc
index f70b021..ba49180 100644 (file)
--- a/BigInteger.cc
+++ b/BigInteger.cc
@@ -310,11 +310,18 @@ BigInteger::CmpRes BigInteger::compareTo(const BigInteger &x) const {
 // These do some messing around to determine the sign of the result,
 // then call one of BigUnsigned's put-heres.
 
+// See remarks about aliased calls in BigUnsigned.cc .
+#define DOTR_ALIASED(cond, op) \
+       if (cond) { \
+               BigInteger tmpThis; \
+               tmpThis.op; \
+               *this = tmpThis; \
+               return; \
+       }
+
 // Addition
 void BigInteger::add(const BigInteger &a, const BigInteger &b) {
-       // Block unsafe calls
-       if (this == &a || this == &b)
-               throw "BigInteger::add: One of the arguments is the invoked object";
+       DOTR_ALIASED(this == &a || this == &b, add(a, b));
        // If one argument is zero, copy the other.
        if (a.sign == zero)
                operator =(b);
@@ -351,9 +358,7 @@ void BigInteger::add(const BigInteger &a, const BigInteger &b) {
 void BigInteger::subtract(const BigInteger &a, const BigInteger &b) {
        // Notice that this routine is identical to BigInteger::add,
        // if one replaces b.sign by its opposite.
-       // Block unsafe calls
-       if (this == &a || this == &b)
-               throw "BigInteger::subtract: One of the arguments is the invoked object";
+       DOTR_ALIASED(this == &a || this == &b, subtract(a, b));
        // If a is zero, copy b and flip its sign.  If b is zero, copy a.
        if (a.sign == zero) {
                BigUnsigned::operator =(b);
@@ -392,9 +397,7 @@ void BigInteger::subtract(const BigInteger &a, const BigInteger &b) {
 
 // Multiplication
 void BigInteger::multiply(const BigInteger &a, const BigInteger &b) {
-       // Block unsafe calls
-       if (this == &a || this == &b)
-               throw "BigInteger::multiply: One of the arguments is the invoked object";
+       DOTR_ALIASED(this == &a || this == &b, multiply(a, b));
        // If one object is zero, copy zero and return.
        if (a.sign == zero || b.sign == zero) {
                sign = zero;
@@ -431,9 +434,16 @@ void BigInteger::multiply(const BigInteger &a, const BigInteger &b) {
 *      -4      -3      1       -1
 */
 void BigInteger::divideWithRemainder(const BigInteger &b, BigInteger &q) {
-       // Block unsafe calls
-       if (this == &b || this == &q || &b == &q)
-               throw "BigInteger::divideWithRemainder: One of the arguments is the invoked object";
+       // Defend against aliased calls;
+       // same idea as in BigUnsigned::divideWithRemainder .
+       if (this == &q)
+               throw "BigInteger::divideWithRemainder: Cannot write quotient and remainder into the same variable";
+       if (this == &b || &q == &b) {
+               BigInteger tmpB(b);
+               divideWithRemainder(tmpB, q);
+               return;
+       }
+       
        // Division by zero gives quotient 0 and remainder *this
        if (b.sign == zero) {
                q.len = 0;
@@ -507,9 +517,7 @@ void BigInteger::divideWithRemainder(const BigInteger &b, BigInteger &q) {
 
 // Negation
 void BigInteger::negate(const BigInteger &a) {
-       // Block unsafe calls
-       if (this == &a)
-               throw "BigInteger::negate: The argument is the invoked object";
+       DOTR_ALIASED(this == &a, negate(a));
        // Copy a's magnitude
        BigUnsigned::operator =(a);
        // Copy the opposite of a.sign