time-to-botec

Benchmark sampling in different programming languages
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sapxsumpw.js (2216B)

      1 /**
      2 * @license Apache-2.0
      3 *
      4 * Copyright (c) 2020 The Stdlib Authors.
      5 *
      6 * Licensed under the Apache License, Version 2.0 (the "License");
      7 * you may not use this file except in compliance with the License.
      8 * You may obtain a copy of the License at
      9 *
     10 *    http://www.apache.org/licenses/LICENSE-2.0
     11 *
     12 * Unless required by applicable law or agreed to in writing, software
     13 * distributed under the License is distributed on an "AS IS" BASIS,
     14 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
     15 * See the License for the specific language governing permissions and
     16 * limitations under the License.
     17 */
     18 
     19 'use strict';
     20 
     21 // MODULES //
     22 
     23 var float64ToFloat32 = require( '@stdlib/number/float64/base/to-float32' );
     24 var sum = require( './ndarray.js' );
     25 
     26 
     27 // MAIN //
     28 
     29 /**
     30 * Adds a constant to each single-precision floating-point strided array element and computes the sum using pairwise summation.
     31 *
     32 * ## Method
     33 *
     34 * -   This implementation uses pairwise summation, which accrues rounding error `O(log2 N)` instead of `O(N)`. The recursion depth is also `O(log2 N)`.
     35 *
     36 * ## References
     37 *
     38 * -   Higham, Nicholas J. 1993. "The Accuracy of Floating Point Summation." _SIAM Journal on Scientific Computing_ 14 (4): 783–99. doi:[10.1137/0914050](https://doi.org/10.1137/0914050).
     39 *
     40 * @param {PositiveInteger} N - number of indexed elements
     41 * @param {number} alpha - constant
     42 * @param {Float32Array} x - input array
     43 * @param {integer} stride - stride length
     44 * @returns {number} sum
     45 *
     46 * @example
     47 * var Float32Array = require( '@stdlib/array/float32' );
     48 *
     49 * var x = new Float32Array( [ 1.0, -2.0, 2.0 ] );
     50 * var N = x.length;
     51 *
     52 * var v = sapxsumpw( N, 5.0, x, 1 );
     53 * // returns 16.0
     54 */
     55 function sapxsumpw( N, alpha, x, stride ) {
     56 	var ix;
     57 	var s;
     58 	var i;
     59 
     60 	if ( N <= 0 ) {
     61 		return 0.0;
     62 	}
     63 	if ( N === 1 || stride === 0 ) {
     64 		return float64ToFloat32( alpha + x[ 0 ] );
     65 	}
     66 	if ( stride < 0 ) {
     67 		ix = (1-N) * stride;
     68 	} else {
     69 		ix = 0;
     70 	}
     71 	if ( N < 8 ) {
     72 		// Use simple summation...
     73 		s = 0.0;
     74 		for ( i = 0; i < N; i++ ) {
     75 			s = float64ToFloat32( s + float64ToFloat32( alpha + x[ ix ] ) );
     76 			ix += stride;
     77 		}
     78 		return s;
     79 	}
     80 	return sum( N, alpha, x, stride, ix );
     81 }
     82 
     83 
     84 // EXPORTS //
     85 
     86 module.exports = sapxsumpw;