## Usage ```javascript var drev = require( '@stdlib/blas/ext/base/drev' ); ``` #### drev( N, x, stride ) Reverses a double-precision floating-point strided array `x` in-place. ```javascript var Float64Array = require( '@stdlib/array/float64' ); var x = new Float64Array( [ -2.0, 1.0, 3.0, -5.0, 4.0, 0.0, -1.0, -3.0 ] ); drev( x.length, x, 1 ); // x => [ -3.0, -1.0, 0.0, 4.0, -5.0, 3.0, 1.0, -2.0 ] ``` The function has the following parameters: - **N**: number of indexed elements. - **x**: input [`Float64Array`][@stdlib/array/float64]. - **stride**: index increment. The `N` and stride parameters determine which elements in the strided array are accessed at runtime. For example, to reverse every other element ```javascript var Float64Array = require( '@stdlib/array/float64' ); var x = new Float64Array( [ -2.0, 1.0, 3.0, -5.0, 4.0, 0.0, -1.0, -3.0 ] ); drev( 4, x, 2 ); // x => [ -1.0, 1.0, 4.0, -5.0, 3.0, 0.0, -2.0, -3.0 ] ``` Note that indexing is relative to the first index. To introduce an offset, use [`typed array`][mdn-typed-array] views. ```javascript var Float64Array = require( '@stdlib/array/float64' ); // Initial array... var x0 = new Float64Array( [ 1.0, -2.0, 3.0, -4.0, 5.0, -6.0 ] ); // Create an offset view... var x1 = new Float64Array( x0.buffer, x0.BYTES_PER_ELEMENT*1 ); // start at 2nd element // Reverse every other element... drev( 3, x1, 2 ); // x0 => [ 1.0, -6.0, 3.0, -4.0, 5.0, -2.0 ] ``` #### drev.ndarray( N, x, stride, offset ) Reverses a double-precision floating-point strided array `x` in-place using alternative indexing semantics. ```javascript var Float64Array = require( '@stdlib/array/float64' ); var x = new Float64Array( [ -2.0, 1.0, 3.0, -5.0, 4.0, 0.0, -1.0, -3.0 ] ); drev.ndarray( x.length, x, 1, 0 ); // x => [ -3.0, -1.0, 0.0, 4.0, -5.0, 3.0, 1.0, -2.0 ] ``` The function has the following additional parameters: - **offset**: starting index. While [`typed array`][mdn-typed-array] views mandate a view offset based on the underlying `buffer`, the `offset` parameter supports indexing semantics based on a starting index. For example, to access only the last three elements of the strided array ```javascript var Float64Array = require( '@stdlib/array/float64' ); var x = new Float64Array( [ 1.0, -2.0, 3.0, -4.0, 5.0, -6.0 ] ); drev.ndarray( 3, x, 1, x.length-3 ); // x => [ 1.0, -2.0, 3.0, -6.0, 5.0, -4.0 ] ```

## Notes - If `N <= 0`, both functions return the strided array unchanged. - Where possible, one should "reverse" a strided array by negating its stride, which is an `O(1)` operation, in contrast to performing an in-place reversal, which is `O(N)`. However, in certain circumstances, this is not tenable, particularly when interfacing with libraries which assume and/or expect a specific memory layout (e.g., strided array elements arranged in memory in ascending order). In general, when working with strided arrays, only perform an in-place reversal when strictly necessary.