diff --git a/packages/as-sha256/src/hashCache.ts b/packages/as-sha256/src/hashCache.ts
index 72aeea9c..601be393 100644
--- a/packages/as-sha256/src/hashCache.ts
+++ b/packages/as-sha256/src/hashCache.ts
@@ -19,19 +19,19 @@ export type HashCache = {
  */
 export type HashId = number;
 
-function toHashId(cacheIndex: number, hashIndex: number): HashId {
+export function toHashId(cacheIndex: number, hashIndex: number): HashId {
   return (cacheIndex << 16) | hashIndex;
 }
 
-function fromHashId(id: HashId): [number, number] {
+export function fromHashId(id: HashId): [number, number] {
   return [id >> 16, id & 0xffff];
 }
 
-function getCacheIndex(id: HashId): number {
+export function getCacheIndex(id: HashId): number {
   return id >> 16;
 }
 
-function getHashIndex(id: HashId): number {
+export function getHashIndex(id: HashId): number {
   return id & 0xffff;
 }
 
@@ -46,13 +46,6 @@ export function allocHashCache(): HashCache {
   return out;
 }
 
-export function getHash(id: HashId): Uint8Array {
-  const [cacheIndex, hashIndex] = fromHashId(id);
-  const cache = hashCaches[cacheIndex];
-  const offset = hashIndex * HASH_SIZE;
-  return cache.cache.subarray(offset, offset + HASH_SIZE);
-}
-
 export function getCache(id: HashId): HashCache {
   return hashCaches[getCacheIndex(id)];
 }
@@ -65,7 +58,7 @@ export function incrementNext(cache: HashCache): number {
   const out = cache.next;
   cache.used.add(out);
   // eslint-disable-next-line no-empty
-  while (cache.used.has(cache.next++)) {}
+  while (cache.used.has(++cache.next)) {}
   return out;
 }
 
@@ -134,6 +127,13 @@ export function cloneHashId(source: HashId, target: HashId): void {
   cacheTarget[offsetTarget++] = cacheSource[offsetSource++];
 }
 
+export function getHash(id: HashId): Uint8Array {
+  const [cacheIndex, hashIndex] = fromHashId(id);
+  const cache = hashCaches[cacheIndex];
+  const offset = hashIndex * HASH_SIZE;
+  return cache.cache.subarray(offset, offset + HASH_SIZE);
+}
+
 export function getHashObject(id: HashId): HashObject {
   const {cache} = getCache(id);
   let offset = getCacheOffset(id);
diff --git a/packages/as-sha256/test/unit/hashCache.test.ts b/packages/as-sha256/test/unit/hashCache.test.ts
index 5182937d..9dc48237 100644
--- a/packages/as-sha256/test/unit/hashCache.test.ts
+++ b/packages/as-sha256/test/unit/hashCache.test.ts
@@ -1,7 +1,29 @@
 import {expect} from "chai";
-import {allocHashId, digest2Bytes32, digest64HashIds, freeHashId, getHash} from "../../src";
+import {CACHE_HASH_SIZE, allocHashId, digest2Bytes32, digest64HashIds, freeHashId, getCache, getHash, getHashIndex} from "../../src";
 
 describe("hash cache", () => {
+  it("should allocate and free hash ids", () => {
+    let id = allocHashId();
+    const hashIndex = getHashIndex(id);
+    if (hashIndex >= CACHE_HASH_SIZE / 2) {
+      console.warn("unreachable");
+      return;
+    }
+
+    const ids = [id];
+    for (let i = 0; i < CACHE_HASH_SIZE - hashIndex; i++) {
+      ids.push(allocHashId());
+    }
+
+    expect(getCache(ids[0]).used.size).to.equal(CACHE_HASH_SIZE);
+
+    for (const id of ids) {
+      freeHashId(id);
+    }
+
+    expect(getCache(ids[0]).used.size).to.equal(Math.max(CACHE_HASH_SIZE - ids.length, 0));
+  });
+
   it("should properly hash many items", function () {
     this.timeout(0);