172 lines
5.0 KiB
Markdown
172 lines
5.0 KiB
Markdown
<!--
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@license Apache-2.0
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Copyright (c) 2018 The Stdlib Authors.
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Licensed under the Apache License, Version 2.0 (the "License");
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you may not use this file except in compliance with the License.
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You may obtain a copy of the License at
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http://www.apache.org/licenses/LICENSE-2.0
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Unless required by applicable law or agreed to in writing, software
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distributed under the License is distributed on an "AS IS" BASIS,
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WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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See the License for the specific language governing permissions and
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limitations under the License.
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-->
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# arraybuffer2buffer
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> Allocate a [buffer][@stdlib/buffer/ctor] from an [ArrayBuffer][@stdlib/array/buffer].
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<!-- Section to include introductory text. Make sure to keep an empty line after the intro `section` element and another before the `/section` close. -->
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<section class="intro">
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</section>
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<!-- /.intro -->
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<!-- Package usage documentation. -->
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<section class="usage">
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## Usage
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```javascript
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var arraybuffer2buffer = require( '@stdlib/buffer/from-arraybuffer' );
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```
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#### arraybuffer2buffer( buf\[, byteOffset\[, length]] )
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Allocates a [buffer][@stdlib/buffer/ctor] from an [`ArrayBuffer`][@stdlib/array/buffer].
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```javascript
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var ArrayBuffer = require( '@stdlib/array/buffer' );
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var ab = new ArrayBuffer( 10 );
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var buf = arraybuffer2buffer( ab );
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// returns <Buffer>
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```
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By default, the function allocates a [buffer][@stdlib/buffer/ctor] starting from the first byte of the provided [`ArrayBuffer`][@stdlib/array/buffer]. To specify an alternative starting index, provide a `byteOffset`.
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```javascript
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var ArrayBuffer = require( '@stdlib/array/buffer' );
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var ab = new ArrayBuffer( 10 );
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var buf = arraybuffer2buffer( ab, 2 );
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// returns <Buffer>
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var len = buf.length;
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// returns 8
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```
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By default, the function allocates a [buffer][@stdlib/buffer/ctor] until the end of the provided [`ArrayBuffer`][@stdlib/array/buffer]. To allocate a specified number of [`ArrayBuffer`][@stdlib/array/buffer] bytes, provide a `length`.
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```javascript
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var ArrayBuffer = require( '@stdlib/array/buffer' );
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var ab = new ArrayBuffer( 10 );
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var buf = arraybuffer2buffer( ab, 2, 4 );
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// returns <Buffer>
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var len = buf.length;
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// returns 4
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```
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</section>
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<!-- /.usage -->
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<!-- Package usage notes. Make sure to keep an empty line after the `section` element and another before the `/section` close. -->
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<section class="notes">
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## Notes
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The behavior of this function varies across Node.js versions due to changes in the underlying Node.js APIs:
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- `<3.0.0`: the function copies [`ArrayBuffer`][@stdlib/array/buffer] bytes to a new [`Buffer`][@stdlib/buffer/ctor] instance.
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- `>=3.0.0` and `<5.10.0`: if provided a `byteOffset`, the function copies [`ArrayBuffer`][@stdlib/array/buffer] bytes to a new [`Buffer`][@stdlib/buffer/ctor] instance; otherwise, the function returns a view of an [`ArrayBuffer`][@stdlib/array/buffer] without copying the underlying memory.
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- `<6.0.0`: if provided an empty [`ArrayBuffer`][@stdlib/array/buffer], the function returns an empty [`Buffer`][@stdlib/buffer/ctor] which is **not** an [`ArrayBuffer`][@stdlib/array/buffer] view.
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- `>=6.0.0`: the function returns a view of an [`ArrayBuffer`][@stdlib/array/buffer] without copying the underlying memory.
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</section>
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<!-- /.notes -->
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<!-- Package usage examples. -->
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<section class="examples">
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## Examples
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<!-- eslint no-undef: "error" -->
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```javascript
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var ArrayBuffer = require( '@stdlib/array/buffer' );
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var Float64Array = require( '@stdlib/array/float64' );
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var randu = require( '@stdlib/random/base/randu' );
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var IS_LITTLE_ENDIAN = require( '@stdlib/assert/is-little-endian' );
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var arraybuffer2buffer = require( '@stdlib/buffer/from-arraybuffer' );
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var high;
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var view;
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var low;
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var buf;
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var ab;
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var i;
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// Allocate an ArrayBuffer:
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ab = new ArrayBuffer( 64 );
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// Create a Float64 view and set random values:
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view = new Float64Array( ab );
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for ( i = 0; i < view.length; i++ ) {
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view[ i ] = randu();
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}
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// Create a new buffer from the ArrayBuffer:
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buf = arraybuffer2buffer( ab );
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// Read the high and low words for each double:
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for ( i = 0; i < view.length; i++ ) {
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if ( IS_LITTLE_ENDIAN ) {
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high = buf.readUInt32LE( (8*i)+4 );
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low = buf.readUInt32LE( 8*i );
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} else {
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high = buf.readUInt32BE( 8*i );
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low = buf.readUInt32BE( (8*i)+4 );
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}
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console.log( 'Value: %d. High: %d. Low: %d.', view[ i ], high, low );
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}
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```
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</section>
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<!-- /.examples -->
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<!-- Section to include cited references. If references are included, add a horizontal rule *before* the section. Make sure to keep an empty line after the `section` element and another before the `/section` close. -->
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<section class="references">
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</section>
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<!-- /.references -->
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<!-- Section for all links. Make sure to keep an empty line after the `section` element and another before the `/section` close. -->
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<section class="links">
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[@stdlib/buffer/ctor]: https://www.npmjs.com/package/@stdlib/buffer/tree/main/ctor
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[@stdlib/array/buffer]: https://www.npmjs.com/package/@stdlib/array-buffer
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</section>
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<!-- /.links -->
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