Changeset 11287

Timestamp:

08/16/08 20:23:16 (15 years ago)

Author:

ehuelsmann

Message:

Repeated squaring instead of repeated multiplication.

Found by: Robert Dodier <robert_dodier--at--yahoo.com>

File:

• trunk/j/src/org/armedbear/lisp/MathFunctions.java (modified) (1 diff)

trunk/j/src/org/armedbear/lisp/MathFunctions.java

@@ -738 +738 @@
                 int pow = ((Fixnum)power).value;
                 if (pow > 0) {
-                    for (int i = pow; i-- > 0;)
-                        result = result.multiplyBy(base);
+                    LispObject term = base;
+                    while (pow != 0) {
+                        if ((pow & 1) == 1)
+                           result = result.multiplyBy(term);
+
+                        term = term.multiplyBy(term);
+                        pow = pow >> 1;
+                    }
                 } else if (pow < 0) {
-                    for (int i = -pow; i-- > 0;)
-                        result = result.divideBy(base);
+                    LispObject term = base;
+                    pow = -pow;
+                    while (pow != 0) {
+                        if ((pow & 1) == 1)
+                           result = result.divideBy(term);
+
+                        term = term.multiplyBy(term);
+                        pow = pow >> 1;
+                    }
                 }
                 if (TRAP_OVERFLOW) {