| 1 | // Copyright 2017-2022 @polkadot/util authors & contributors
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| 2 | // SPDX-License-Identifier: Apache-2.0
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| 3 |
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| 4 | /**
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| 5 | * @name u8aFixLength
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| 6 | * @summary Shifts a Uint8Array to a specific bitLength
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| 7 | * @description
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| 8 | * Returns a uint8Array with the specified number of bits contained in the return value. (If bitLength is -1, length checking is not done). Values with more bits are trimmed to the specified length.
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| 9 | * @example
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| 10 | * <BR>
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| 11 | *
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| 12 | * ```javascript
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| 13 | * import { u8aFixLength } from '@polkadot/util';
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| 14 | *
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| 15 | * u8aFixLength('0x12') // => 0x12
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| 16 | * u8aFixLength('0x12', 16) // => 0x0012
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| 17 | * u8aFixLength('0x1234', 8) // => 0x12
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| 18 | * ```
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| 19 | */
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| 20 | export function u8aFixLength(value, bitLength = -1, atStart = false) {
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| 21 | const byteLength = Math.ceil(bitLength / 8);
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| 22 |
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| 23 | if (bitLength === -1 || value.length === byteLength) {
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| 24 | return value;
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| 25 | } else if (value.length > byteLength) {
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| 26 | return value.subarray(0, byteLength);
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| 27 | }
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| 28 |
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| 29 | const result = new Uint8Array(byteLength);
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| 30 | result.set(value, atStart ? 0 : byteLength - value.length);
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| 31 | return result;
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| 32 | } |
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