feat: rework crc16 function and cover it with tests (#1739)

dev-docs/CHANGELOG.md

@@ -47,6 +47,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - Better error message for `extend function without parameters` error: PR [#1624](https://github.com/tact-lang/tact/pull/1624)
 - Don't generate `lazy_deployment_completed` by default: PR [#1717](https://github.com/tact-lang/tact/pull/1717)
 - Optimized `emptyCell()` and `emptySlice()` functions: PR [#1696](https://github.com/tact-lang/tact/pull/1696)
+- Internal `crc16` function is now verifiable and covered with tests: PR [#1739](https://github.com/tact-lang/tact/pull/1739)
 - Rearrange parameters of some asm methods in order described in `AsmShuffle`: PR [#1702](https://github.com/tact-lang/tact/pull/1702)
 - Error message for invalid type for function argument now shows expected type: PR [#1738](https://github.com/tact-lang/tact/pull/1738)
 

spell/cspell-list.txt

@@ -15,6 +15,7 @@ cheatsheet
 Cheatsheet
 cheatsheets
 Cheatsheets
+CCITT
 cleanall
 codegen
 compilables
@@ -167,5 +168,6 @@ vogons
 workchain
 workchains
 xffff
+XMODEM
 xtwitter
 привет

src/utils/crc16.spec.ts

@@ -0,0 +1,16 @@
+import { crc16 } from "./crc16";
+
+describe("crc16", () => {
+    it("crc16 is correctly calculated from the string", () => {
+        expect(crc16("")).toBe(0);
+        expect(crc16("Hello Tact")).toBe(11154);
+        expect(crc16("Привет Tact")).toBe(36467);
+        expect(crc16("👋 Tact")).toBe(17840);
+        expect(crc16("\u0000")).toBe(0);
+        expect(crc16("⚡")).toBe(40122);
+
+        expect((crc16("get_wallet_data") & 0xffff) | 0x10000).toBe(97026);
+        expect((crc16("get_jetton_data") & 0xffff) | 0x10000).toBe(106029);
+        expect((crc16("get_wallet_address") & 0xffff) | 0x10000).toBe(103289);
+    });
+});

src/utils/crc16.ts

@@ -1,46 +1,37 @@
-const TABLE = new Int16Array([
-    0x0000, 0x1021, 0x2042, 0x3063, 0x4084, 0x50a5, 0x60c6, 0x70e7, 0x8108,
-    0x9129, 0xa14a, 0xb16b, 0xc18c, 0xd1ad, 0xe1ce, 0xf1ef, 0x1231, 0x0210,
-    0x3273, 0x2252, 0x52b5, 0x4294, 0x72f7, 0x62d6, 0x9339, 0x8318, 0xb37b,
-    0xa35a, 0xd3bd, 0xc39c, 0xf3ff, 0xe3de, 0x2462, 0x3443, 0x0420, 0x1401,
-    0x64e6, 0x74c7, 0x44a4, 0x5485, 0xa56a, 0xb54b, 0x8528, 0x9509, 0xe5ee,
-    0xf5cf, 0xc5ac, 0xd58d, 0x3653, 0x2672, 0x1611, 0x0630, 0x76d7, 0x66f6,
-    0x5695, 0x46b4, 0xb75b, 0xa77a, 0x9719, 0x8738, 0xf7df, 0xe7fe, 0xd79d,
-    0xc7bc, 0x48c4, 0x58e5, 0x6886, 0x78a7, 0x0840, 0x1861, 0x2802, 0x3823,
-    0xc9cc, 0xd9ed, 0xe98e, 0xf9af, 0x8948, 0x9969, 0xa90a, 0xb92b, 0x5af5,
-    0x4ad4, 0x7ab7, 0x6a96, 0x1a71, 0x0a50, 0x3a33, 0x2a12, 0xdbfd, 0xcbdc,
-    0xfbbf, 0xeb9e, 0x9b79, 0x8b58, 0xbb3b, 0xab1a, 0x6ca6, 0x7c87, 0x4ce4,
-    0x5cc5, 0x2c22, 0x3c03, 0x0c60, 0x1c41, 0xedae, 0xfd8f, 0xcdec, 0xddcd,
-    0xad2a, 0xbd0b, 0x8d68, 0x9d49, 0x7e97, 0x6eb6, 0x5ed5, 0x4ef4, 0x3e13,
-    0x2e32, 0x1e51, 0x0e70, 0xff9f, 0xefbe, 0xdfdd, 0xcffc, 0xbf1b, 0xaf3a,
-    0x9f59, 0x8f78, 0x9188, 0x81a9, 0xb1ca, 0xa1eb, 0xd10c, 0xc12d, 0xf14e,
-    0xe16f, 0x1080, 0x00a1, 0x30c2, 0x20e3, 0x5004, 0x4025, 0x7046, 0x6067,
-    0x83b9, 0x9398, 0xa3fb, 0xb3da, 0xc33d, 0xd31c, 0xe37f, 0xf35e, 0x02b1,
-    0x1290, 0x22f3, 0x32d2, 0x4235, 0x5214, 0x6277, 0x7256, 0xb5ea, 0xa5cb,
-    0x95a8, 0x8589, 0xf56e, 0xe54f, 0xd52c, 0xc50d, 0x34e2, 0x24c3, 0x14a0,
-    0x0481, 0x7466, 0x6447, 0x5424, 0x4405, 0xa7db, 0xb7fa, 0x8799, 0x97b8,
-    0xe75f, 0xf77e, 0xc71d, 0xd73c, 0x26d3, 0x36f2, 0x0691, 0x16b0, 0x6657,
-    0x7676, 0x4615, 0x5634, 0xd94c, 0xc96d, 0xf90e, 0xe92f, 0x99c8, 0x89e9,
-    0xb98a, 0xa9ab, 0x5844, 0x4865, 0x7806, 0x6827, 0x18c0, 0x08e1, 0x3882,
-    0x28a3, 0xcb7d, 0xdb5c, 0xeb3f, 0xfb1e, 0x8bf9, 0x9bd8, 0xabbb, 0xbb9a,
-    0x4a75, 0x5a54, 0x6a37, 0x7a16, 0x0af1, 0x1ad0, 0x2ab3, 0x3a92, 0xfd2e,
-    0xed0f, 0xdd6c, 0xcd4d, 0xbdaa, 0xad8b, 0x9de8, 0x8dc9, 0x7c26, 0x6c07,
-    0x5c64, 0x4c45, 0x3ca2, 0x2c83, 0x1ce0, 0x0cc1, 0xef1f, 0xff3e, 0xcf5d,
-    0xdf7c, 0xaf9b, 0xbfba, 0x8fd9, 0x9ff8, 0x6e17, 0x7e36, 0x4e55, 0x5e74,
-    0x2e93, 0x3eb2, 0x0ed1, 0x1ef0,
-]);
-
-export function crc16(data: string | Buffer) {
-    if (!(data instanceof Buffer)) {
-        data = Buffer.from(data);
+/**
+ * Generates the CRC16 lookup table for the given polynomial.
+ * (Using polynomial 0x1021)
+ */
+function makeCRC16Table(polynomial: number): Uint16Array {
+    const table = new Uint16Array(256);
+    for (let n = 0; n < 256; n++) {
+        // Initialize crc for this byte. (Note the left shift by 8)
+        let crc = n << 8;
+        for (let k = 0; k < 8; k++) {
+            crc = (crc & 0x8000 ? (crc << 1) ^ polynomial : crc << 1) & 0xffff;
+        }
+        table[n] = crc;
     }
+    return table;
+}
 
-    let crc = 0;
+// Precompute the CRC-16-CCITT (XMODEM) table once at module load.
+const CRC16_TABLE = makeCRC16Table(0x1021);
 
-    data.forEach(
-        (byte) =>
-            (crc = (TABLE[((crc >> 8) ^ byte) & 0xff]! ^ (crc << 8)) & 0xffff),
-    );
+/**
+ * Computes the CRC16 checksum of the given data.
+ *
+ * @param data - A string or Uint8Array to compute the checksum for.
+ * @returns The computed CRC16 checksum.
+ */
+export function crc16(data: string | Uint8Array): number {
+    if (typeof data === "string") {
+        data = new TextEncoder().encode(data);
+    }
 
+    let crc = 0;
+    for (const byte of data) {
+        crc = ((crc << 8) ^ CRC16_TABLE[((crc >> 8) ^ byte) & 0xff]!) & 0xffff;
+    }
     return crc;
 }