feat: add overflow warning

Author: wan2land

cli.ts

@@ -14,16 +14,15 @@ const args = parse(rawArgs);
 
 const bit = args.b ?? args.bit ?? args.bits ?? 53;
 const options = Hasher.generate(bit);
+const hasher = new Hasher(options);
 
 console.log(JSON.stringify(options, null, "  "));
 console.error(`
 $ ${cmd}${cmdSuffix ? " " + cmdSuffix : ""} | pbcopy
 
 Now go ahead and paste it into your code! Good luck. :-)
 
-Note: The supported range of integers is from min: 0 to max: ${
-  (1n << BigInt(bit)) - 1n
-}.
+Note: The supported range of integers is from min: 0 to max: ${hasher._max}.
 Please make sure your inputs fall within this range.`);
 
 type Args = {

deno.json

@@ -11,8 +11,9 @@
   },
   "imports": {
     "@deno/dnt": "jsr:@deno/dnt@^0.41.1",
-    "@std/assert": "jsr:@std/assert@^0.221.0",
-    "@std/fmt": "jsr:@std/fmt@^0.221.0"
+    "@std/assert": "jsr:@std/assert@^0.222.0",
+    "@std/fmt": "jsr:@std/fmt@^0.222.0",
+    "@std/testing": "jsr:@std/testing@^0.222.1"
   },
   "exports": {
     ".": "./mod.ts",

hasher.test.ts

@@ -1,4 +1,5 @@
 import { assertEquals, assertNotEquals } from "@std/assert";
+import { assertSpyCall, assertSpyCalls, spy } from "@std/testing/mock";
 import { Hasher } from "./hasher.ts";
 
 Deno.test("hasher, encode and decode", () => {
@@ -82,6 +83,18 @@ Deno.test("full coverage of 8bit", () => {
     for (let i = 0; i < 256; i++) {
       assertEquals(hasher.decode(hasher.encode(i)), i);
     }
-    assertEquals(hasher.decode(hasher.encode(256)), 0); // overflow
   }
 });
+
+Deno.test("overflow", () => {
+  const hasher = new Hasher(Hasher.generate(8));
+
+  const logSpy = spy(console, "warn");
+
+  hasher.encode(256);
+
+  assertSpyCall(logSpy, 0, {
+    args: ["input 256 is greater than max 255"],
+  });
+  assertSpyCalls(logSpy, 1);
+});

hasher.ts

@@ -51,12 +51,14 @@ export class Hasher {
   _inverse: bigint;
   _xor: bigint;
   _mask: bigint;
+  _max: bigint;
 
   constructor({ bits, prime, inverse, xor }: HasherOptions) {
     this._prime = BigInt(prime);
     this._inverse = BigInt(inverse);
     this._xor = BigInt(xor);
     this._mask = 2n ** BigInt(bits) - 1n;
+    this._max = (1n << BigInt(bits)) - 1n;
   }
 
   encode(n: number): number;
@@ -69,6 +71,9 @@ export class Hasher {
     if (typeof n === "number") {
       return Number(this.encode(BigInt(n)));
     }
+    if (n > this._max) {
+      console.warn(`input ${n} is greater than max ${this._max}`);
+    }
     return n * this._prime & this._mask ^ this._xor;
   }