98 lines
2.3 KiB
Markdown
98 lines
2.3 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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# imuldw
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> Compute the double word product of two signed 32-bit integers.
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<section class="intro">
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</section>
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<!-- /.intro -->
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<section class="usage">
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## Usage
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```javascript
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var imuldw = require( '@stdlib/math/base/special/imuldw' );
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```
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#### imuldw( \[out,] a, b )
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Multiplies two signed 32-bit integers and returns an `array` of two signed 32-bit integers which represents the signed 64-bit integer product.
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```javascript
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var v = imuldw( 1, 10 );
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// returns [ 0, 10 ]
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v = imuldw( 0x80000000|0, 0x40000000|0 ); // -(2^31) * 2^30 = -2305843009213694000 => 32-bit integer overflow
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// returns [ -536870912, 0 ]
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```
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</section>
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<!-- /.usage -->
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<section class="notes">
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## Notes
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- When computing the product of 32-bit integer values in double-precision floating-point format (the default JavaScript numeric data type), computing the double word product is necessary in order to **avoid** exceeding the [maximum safe double-precision floating-point integer value][@stdlib/constants/float64/max-safe-integer].
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</section>
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<!-- /.notes -->
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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 lpad = require( '@stdlib/string/left-pad' );
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var imuldw = require( '@stdlib/math/base/special/imuldw' );
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var i;
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var j;
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var y;
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for ( i = 0x7FFFFFF0; i < 0x7FFFFFFF; i++ ) {
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for ( j = i; j < 0x7FFFFFFF; j++) {
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y = imuldw( i|0, j|0 );
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console.log( '%d x %d = 0x%s%s', i|0, j|0, lpad( ( y[0] >>> 0 ).toString( 16 ), 8, '0'), lpad( ( y[1] >>> 0 ).toString( 16 ), 8, '0' ) );
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}
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}
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```
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</section>
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<!-- /.examples -->
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<section class="links">
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[@stdlib/constants/float64/max-safe-integer]: https://www.npmjs.com/package/@stdlib/constants-float64-max-safe-integer
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</section>
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<!-- /.links -->
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