// Copyright 2018-2025 the Deno authors. MIT license.
// This module is browser compatible.
/**
* Copy bytes from the source array to the destination array and returns the
* number of bytes copied.
*
* If the source array is larger than what the `dst` array can hold, only the
* amount of bytes that fit in the `dst` array are copied.
*
* @param src Source array to copy from.
* @param dst Destination array to copy to.
* @param offset Offset in the destination array to start copying to. Defaults
* to 0.
* @returns Number of bytes copied.
*
* @example Basic usage
* ```ts
* import { copy } from "@std/bytes/copy";
* import { assertEquals } from "@std/assert";
*
* const src = new Uint8Array([9, 8, 7]);
* const dst = new Uint8Array([0, 1, 2, 3, 4, 5]);
*
* assertEquals(copy(src, dst), 3);
* assertEquals(dst, new Uint8Array([9, 8, 7, 3, 4, 5]));
* ```
*
* @example Copy with offset
* ```ts
* import { copy } from "@std/bytes/copy";
* import { assertEquals } from "@std/assert";
*
* const src = new Uint8Array([1, 1, 1, 1]);
* const dst = new Uint8Array([0, 0, 0, 0]);
*
* assertEquals(copy(src, dst, 1), 3);
* assertEquals(dst, new Uint8Array([0, 1, 1, 1]));
* ```
* Defining an offset will start copying at the specified index in the
* destination array.
*/
export function copy(src: Uint8Array, dst: Uint8Array, offset = 0): number {
offset = Math.max(0, Math.min(offset, dst.byteLength));
const dstBytesAvailable = dst.byteLength - offset;
if (src.byteLength > dstBytesAvailable) {
src = src.subarray(0, dstBytesAvailable);
}
dst.set(src, offset);
return src.byteLength;
}
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