X-Git-Url: https://mattmccutchen.net/bigint/bigint.git/blobdiff_plain/3e1327901d299a537a8d932c49dd330f87ac3bda..HEAD:/BigInteger.hh

diff --git a/BigInteger.hh b/BigInteger.hh
index 11be062..cf6e910 100644
--- a/BigInteger.hh
+++ b/BigInteger.hh
@@ -157,12 +157,14 @@ inline BigInteger BigInteger::operator *(const BigInteger &x) const {
 	return ans;
 }
 inline BigInteger BigInteger::operator /(const BigInteger &x) const {
+	if (x.isZero()) throw "BigInteger::operator /: division by zero";
 	BigInteger q, r;
 	r = *this;
 	r.divideWithRemainder(x, q);
 	return q;
 }
 inline BigInteger BigInteger::operator %(const BigInteger &x) const {
+	if (x.isZero()) throw "BigInteger::operator %: division by zero";
 	BigInteger q, r;
 	r = *this;
 	r.divideWithRemainder(x, q);
@@ -191,18 +193,19 @@ inline void BigInteger::operator *=(const BigInteger &x) {
 	multiply(*this, x);
 }
 inline void BigInteger::operator /=(const BigInteger &x) {
-	// Updated for divideWithRemainder
-	BigInteger thisCopy(*this);
-	thisCopy.divideWithRemainder(x, *this);
-	// quotient left in *this
-	// don't care about remainder left in thisCopy
+	if (x.isZero()) throw "BigInteger::operator /=: division by zero";
+	/* The following technique is slightly faster than copying *this first
+	 * when x is large. */
+	BigInteger q;
+	divideWithRemainder(x, q);
+	// *this contains the remainder, but we overwrite it with the quotient.
+	*this = q;
 }
 inline void BigInteger::operator %=(const BigInteger &x) {
-	// Shortcut (woohoo!)
+	if (x.isZero()) throw "BigInteger::operator %=: division by zero";
 	BigInteger q;
+	// Mods *this by x.  Don't care about quotient left in q.
 	divideWithRemainder(x, q);
-	// remainder left in *this
-	// don't care about quotient left in q
 }
 // This one is trivial
 inline void BigInteger::flipSign() {