@polkadot/util
Version:
A collection of useful utilities for @polkadot
49 lines (48 loc) • 1.72 kB
JavaScript
;
Object.defineProperty(exports, "__esModule", { value: true });
exports.compactToU8a = compactToU8a;
const index_js_1 = require("../bn/index.js");
const index_js_2 = require("../u8a/index.js");
const MAX_U8 = index_js_1.BN_TWO.pow(new index_js_1.BN(8 - 2)).isub(index_js_1.BN_ONE);
const MAX_U16 = index_js_1.BN_TWO.pow(new index_js_1.BN(16 - 2)).isub(index_js_1.BN_ONE);
const MAX_U32 = index_js_1.BN_TWO.pow(new index_js_1.BN(32 - 2)).isub(index_js_1.BN_ONE);
const BL_16 = { bitLength: 16 };
const BL_32 = { bitLength: 32 };
/**
* @name compactToU8a
* @description Encodes a number into a compact representation
* @example
* <BR>
*
* ```javascript
* import { compactToU8a } from '@polkadot/util';
*
* console.log(compactToU8a(511, 32)); // Uint8Array([0b11111101, 0b00000111])
* ```
*/
function compactToU8a(value) {
const bn = (0, index_js_1.bnToBn)(value);
if (bn.lte(MAX_U8)) {
return new Uint8Array([bn.toNumber() << 2]);
}
else if (bn.lte(MAX_U16)) {
return (0, index_js_1.bnToU8a)(bn.shln(2).iadd(index_js_1.BN_ONE), BL_16);
}
else if (bn.lte(MAX_U32)) {
return (0, index_js_1.bnToU8a)(bn.shln(2).iadd(index_js_1.BN_TWO), BL_32);
}
const u8a = (0, index_js_1.bnToU8a)(bn);
let length = u8a.length;
// adjust to the minimum number of bytes
while (u8a[length - 1] === 0) {
length--;
}
if (length < 4) {
throw new Error('Invalid length, previous checks match anything less than 2^30');
}
return (0, index_js_2.u8aConcatStrict)([
// subtract 4 as minimum (also catered for in decoding)
new Uint8Array([((length - 4) << 2) + 0b11]),
u8a.subarray(0, length)
]);
}