diff --git a/src/algorithm.ts b/src/algorithm.ts
index 452200c..cd30000 100644
--- a/src/algorithm.ts
+++ b/src/algorithm.ts
@@ -23,3 +23,29 @@ export function binSearch(begin: number, end: number, beforeHalf: boolean[]): [n
 
     return [begin, half, end];
 }
+
+export async function autoBisect(
+    begin: number,
+    end: number,
+    check: (
+        begin: number,
+        end: number,
+        index: number
+    ) => Promise<boolean>) {
+
+    // Try to find the first index where check() predicates to true.
+    // Assume check() is true at first, for range [begin, end)
+    let index = 0;
+    while (end - begin > 1) {
+        const mid = Math.floor((end - begin) / 2) + begin;
+        if (await check(begin, mid, index)) {
+            // Shrink half range.
+            end = mid;
+        } else {
+            begin = mid;
+        }
+        index++;
+    }
+
+    return begin;
+}