145 lines
3.6 KiB
Markdown
145 lines
3.6 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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# Promotion Rules
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> Return the ndarray [data type][@stdlib/ndarray/dtypes] with the smallest size and closest "kind" to which ndarray [data types][@stdlib/ndarray/dtypes] can be **safely** cast.
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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 promotionRules = require( '@stdlib/ndarray/promotion-rules' );
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```
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#### promotionRules( \[dtype1, dtype2] )
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If provided [data types][@stdlib/ndarray/dtypes], returns the ndarray [data type][@stdlib/ndarray/dtypes] with the smallest size and closest "kind" to which ndarray [data types][@stdlib/ndarray/dtypes] can be **safely** cast.
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```javascript
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var out = promotionRules( 'float32', 'uint32' );
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// returns 'float64'
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```
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If a [data type][@stdlib/ndarray/dtypes] to which [data types][@stdlib/ndarray/dtypes] can be safely cast does **not** exist (or is not supported), the function returns `-1`.
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```javascript
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var out = promotionRules( 'binary', 'generic' );
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// returns -1
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```
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If not provided [data types][@stdlib/ndarray/dtypes], the function returns a promotion table.
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```javascript
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var out = promotionRules();
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// returns {...}
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var f32 = out[ 'float32' ];
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// returns {...}
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var rule = f32[ 'uint32' ];
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// returns 'float64'
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```
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If provided an unrecognized or unsupported `dtype`, the function returns `null`.
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```javascript
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var out = promotionRules( 'foo', 'generic' );
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// returns null
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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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</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 dtypes = require( '@stdlib/ndarray/dtypes' );
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var promotionRules = require( '@stdlib/ndarray/promotion-rules' );
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var DTYPES;
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var dt1;
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var dt2;
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var dt;
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var i;
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var j;
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// Get the list of supported ndarray data types:
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DTYPES = dtypes();
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// Print the promotion rule for each pair of ndarray data types...
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for ( i = 0; i < DTYPES.length; i++ ) {
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dt1 = DTYPES[ i ];
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for ( j = 0; j < DTYPES.length; j++ ) {
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dt2 = DTYPES[ j ];
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dt = promotionRules( dt1, dt2 );
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console.log( '(%s, %s) => %s', dt1, dt2, dt );
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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 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/ndarray/dtypes]: https://www.npmjs.com/package/@stdlib/ndarray/tree/main/dtypes
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</section>
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<!-- /.links -->
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