1 files changed, 39 insertions, 0 deletions
diff --git a/src/third_party/js-1.7/perfect.js b/src/third_party/js-1.7/perfect.js
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index 00000000000..aeca121186b
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+++ b/src/third_party/js-1.7/perfect.js
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+// Some simple testing of new, eval and some string stuff.
+
+// constructor -- expression array initialization
+function ExprArray(n,v)
+{
+    // Initializes n values to v coerced to a string.
+    for (var i = 0; i < n; i++) {
+	this[i] = "" + v;
+    }
+}
+
+
+// Print the perfect numbers up to n and the sum expression for n's divisors.
+function perfect(n)
+{
+    print("The perfect numbers up to " +  n + " are:");
+
+    // We build sumOfDivisors[i] to hold a string expression for
+    // the sum of the divisors of i, excluding i itself.
+    var sumOfDivisors = new ExprArray(n+1,1);
+    for (var divisor = 2; divisor <= n; divisor++) {
+	for (var j = divisor + divisor; j <= n; j += divisor) {
+	    sumOfDivisors[j] += " + " + divisor;
+	}
+	// At this point everything up to 'divisor' has its sumOfDivisors
+	// expression calculated, so we can determine whether it's perfect
+	// already by evaluating.
+	if (eval(sumOfDivisors[divisor]) == divisor) {
+	    print("" + divisor + " = " + sumOfDivisors[divisor]);
+	}
+    }
+    print("That's all.");
+}
+
+
+print("\nA number is 'perfect' if it is equal to the sum of its")
+print("divisors (excluding itself).\n");
+perfect(500);
+