| 1 | // Copyright 2017-2022 @polkadot/util authors & contributors
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| 2 | // SPDX-License-Identifier: Apache-2.0
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| 3 | import { BN } from "../bn/index.js";
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| 4 | import { u8aToBn, u8aToU8a } from "../u8a/index.js";
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| 5 | /**
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| 6 | * @name compactFromU8a
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| 7 | * @description Retrives the offset and encoded length from a compact-prefixed value
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| 8 | * @example
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| 9 | * <BR>
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| 10 | *
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| 11 | * ```javascript
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| 12 | * import { compactFromU8a } from '@polkadot/util';
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| 13 | *
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| 14 | * const [offset, length] = compactFromU8a(new Uint8Array([254, 255, 3, 0]));
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| 15 | *
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| 16 | * console.log('value offset=', offset, 'length=', length); // 4, 0xffff
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| 17 | * ```
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| 18 | */
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| 19 |
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| 20 | export function compactFromU8a(input) {
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| 21 | const u8a = u8aToU8a(input);
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| 22 | const flag = u8a[0] & 0b11; // The u8a is manually converted here, it is 2x faster that doing an
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| 23 | // additional call to u8aToBn
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| 24 |
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| 25 | if (flag === 0b00) {
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| 26 | return [1, new BN(u8a[0] >>> 2)];
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| 27 | } else if (flag === 0b01) {
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| 28 | return [2, new BN(u8a[0] + u8a[1] * 0x100 >>> 2)];
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| 29 | } else if (flag === 0b10) {
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| 30 | return [4, new BN(u8a[0] + u8a[1] * 0x100 + u8a[2] * 0x10000 + u8a[3] * 0x1000000 >>> 2)];
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| 31 | } // add 5 to shifted (4 for base length, 1 for this byte)
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| 32 |
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| 33 |
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| 34 | const offset = (u8a[0] >>> 2) + 5;
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| 35 | return [offset, u8aToBn(u8a.subarray(1, offset))];
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| 36 | } |
| \ | No newline at end of file |