Optimize findOverlap.

In most cases, append() appends something to the last of
the existing ranges, so we iterate ranges in the reverse order.
This matters if the ranges are heavily fragmentated.

Author: smikitky

multi-integer-range.ts

@@ -151,28 +151,26 @@ export class MultiRange {
 		//
 		// findOverlap(C) returns { lo: 3, count: 0, union: <i-k> }
 		// meaning (C) is between (2) and (3) but overlaps/touches neither of them.
-		//
 
-		let lim = this.ranges.length;
-		for (let lo = 0; lo < lim; lo++) {
-			let r = this.ranges[lo];
+		for (let hi = this.ranges.length - 1; hi >= 0; hi--) {
+			let r = this.ranges[hi];
 			let union;
 			if (union = this.calcUnion(r, target)) {
 				let count = 1;
 				let tmp;
-				while ((lo + count < lim) && (tmp = this.calcUnion(union, this.ranges[lo+count]))) {
+				while ((hi - count >= 0) && (tmp = this.calcUnion(union, this.ranges[hi - count]))) {
 					union = tmp;
 					count++;
 				}
 				// The given target touches or overlaps one or more of the existing ranges
-				return { lo, count, union };
-			} else if (r[0] > target[1] + 1) {
+				return { lo: hi + 1 - count, count, union };
+			} else if (r[1] < target[0]) {
 				// The given target does not touch nor overlap the existing ranges
-				return { lo, count: 0, union: target }
+				return { lo: hi + 1, count: 0, union: target };
 			}
 		}
-		// The given target is larger than the largest existing range
-		return { lo: lim, count: 0, union: target };
+		// The given target is smaller than the smallest existing range
+		return { lo: 0, count: 0, union: target };
 	}