perf(core): binary search for findIndex

src/core/cache.ts

@@ -1,5 +1,5 @@
 import { type InternalCacheSnapshot, type ItemsRange } from "./types";
-import { clamp, max, median, min } from "./utils";
+import { clamp, floor, max, median, min } from "./utils";
 
 type Writeable<T> = {
  -readonly [key in keyof T]: Writeable<T[key]>;
@@ -93,22 +93,34 @@ export const computeTotalSize = (cache: Cache): number => {
 };
 
 /**
+ * Finds the index of an item in the cache whose computed offset is closest to the specified offset.
+ *
  * @internal
  */
 export const findIndex = (cache: Cache, offset: number, i: number): number => {
- while (i >= 0 && i < cache._length) {
- const itemOffset = computeOffset(cache, i);
+ // Find with binary search
+ let low = 0;
+ let high = cache._length - 1;
+
+ if (computeOffset(cache, i) <= offset) {
+ low = i; // Start searching from initialIndex -> up
+ } else {
+ high = i; // Start searching from initialIndex -> down
+ }
+
+ while (low <= high) {
+ const mid = floor((low + high) / 2);
+ const itemOffset = computeOffset(cache, mid);
  if (itemOffset <= offset) {
- if (itemOffset + getItemSize(cache, i) > offset) {
- break;
- } else {
- i++;
+ if (itemOffset + getItemSize(cache, mid) > offset) {
+ return mid;
  }
+ low = mid + 1;
  } else {
- i--;
+ high = mid - 1;
  }
  }
- return clamp(i, 0, cache._length - 1);
+ return clamp(low, 0, cache._length - 1);
 };
 
 /**
@@ -185,7 +197,7 @@ export const initCache = (
  * @internal
  */
 export const takeCacheSnapshot = (cache: Cache): InternalCacheSnapshot => {
- return [[...cache._sizes], cache._defaultItemSize];
+ return [cache._sizes.slice(), cache._defaultItemSize];
 };
 
 /**

src/core/utils.ts

@@ -2,7 +2,7 @@
 export const NULL = null;
 
 /** @internal */
-export const { min, max, abs } = Math;
+export const { min, max, abs, floor } = Math;
 /** @internal */
 export const values = Object.values;
 /** @internal */