Merge pull request #4 from zsqk/feat-u8a-int

feat: add u8aToInt, intToU8a

js/int.test.ts

@@ -0,0 +1,15 @@
+import { assertEquals } from 'https://deno.land/[email protected]/testing/asserts.ts';
+import { intToU8a, u8aToInt } from './int.ts';
+
+Deno.test('u8aToInt', () => {
+  assertEquals(u8aToInt(new Uint8Array([0, 0, 0, 25])), 25);
+  assertEquals(u8aToInt(new Uint8Array([1, 145])), 401);
+});
+
+Deno.test('intToU8a', () => {
+  assertEquals(intToU8a(25, { l: 4 }), new Uint8Array([0, 0, 0, 25]));
+  assertEquals(intToU8a(401, { l: 2 }), new Uint8Array([1, 145]));
+  assertEquals(intToU8a(1048576, { l: 1 }), new Uint8Array([0]));
+  assertEquals(intToU8a(25, { l: 'auto' }), new Uint8Array([25]));
+  assertEquals(intToU8a(401, { l: 'auto' }), new Uint8Array([1, 145]));
+});

js/int.ts

@@ -0,0 +1,53 @@
+/**
+ * Uint8Array to number
+ * - `[ 0, 0, 0, 25 ]` => `25`
+ * - `[ 1, 145 ]` => `401`
+ * @param u8a 一个 Uint8Array 格式的数据.
+ * @returns 一个十进制整数.
+ */
+export function u8aToInt(u8a: Uint8Array): number {
+  let n = 0;
+  for (let i = 0; i < u8a.length; i++) {
+    const m = u8a.length - i - 1;
+    if (m === 0) {
+      n += u8a[i];
+    } else {
+      n += m * 256 * u8a[i];
+    }
+  }
+  return n;
+}
+
+/**
+ * int(number) to Uint8Array
+ * @param int 一个十进制整数.
+ * @returns 一个 Uint8Array 格式的数据.
+ */
+export function intToU8a(
+  int: number,
+  { l = 'auto' }: { l?: number | 'auto' } = {},
+): Uint8Array {
+  let left = int;
+  if (typeof l === 'number') {
+    const arr: number[] = Array(l);
+    for (let i = l - 1; i > -1; i--) {
+      const n = left % 256;
+      arr[i] = n;
+      left = Math.trunc(left / 256);
+    }
+    if (left > 0) {
+      console.warn(`intToU8a left ${left} * 256 * ${l}`);
+    }
+    return new Uint8Array(arr);
+  }
+  const arr: number[] = [];
+  do {
+    const n = left % 256;
+    arr.push(n);
+    left = Math.trunc(left / 256);
+    if (left === 0) {
+      break;
+    }
+  } while (true);
+  return new Uint8Array(arr.reverse());
+}