@polkadot/util
Version:
A collection of useful utilities for @polkadot
46 lines (45 loc) • 1.44 kB
JavaScript
import { BN, BN_ONE, BN_TWO, bnToBn, bnToU8a } from '../bn/index.js';
import { u8aConcatStrict } from '../u8a/index.js';
const MAX_U8 = BN_TWO.pow(new BN(8 - 2)).isub(BN_ONE);
const MAX_U16 = BN_TWO.pow(new BN(16 - 2)).isub(BN_ONE);
const MAX_U32 = BN_TWO.pow(new BN(32 - 2)).isub(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])
* ```
*/
export function compactToU8a(value) {
const bn = bnToBn(value);
if (bn.lte(MAX_U8)) {
return new Uint8Array([bn.toNumber() << 2]);
}
else if (bn.lte(MAX_U16)) {
return bnToU8a(bn.shln(2).iadd(BN_ONE), BL_16);
}
else if (bn.lte(MAX_U32)) {
return bnToU8a(bn.shln(2).iadd(BN_TWO), BL_32);
}
const u8a = 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 u8aConcatStrict([
// subtract 4 as minimum (also catered for in decoding)
new Uint8Array([((length - 4) << 2) + 0b11]),
u8a.subarray(0, length)
]);
}