fix: update implementation to preserve signed zeros

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---

Author: kgryte

lib/node_modules/@stdlib/blas/ext/base/dssumpw/lib/ndarray.js

@@ -78,11 +78,11 @@ function dssumpw( N, x, strideX, offsetX ) {
 	if ( strideX === 0 ) {
 		return N * x[ ix ];
 	}
-
 	if ( N < 8 ) {
 		// Use simple summation...
-		s = 0.0;
-		for ( i = 0; i < N; i++ ) {
+		s = x[ ix ];
+		ix += strideX;
+		for ( i = 1; i < N; i++ ) {
 			s += x[ ix ];
 			ix += strideX;
 		}
@@ -116,7 +116,7 @@ function dssumpw( N, x, strideX, offsetX ) {
 		s = ( (s0+s1) + (s2+s3) ) + ( (s4+s5) + (s6+s7) );
 
 		// Clean-up loop...
-		for ( i; i < N; i++ ) {
+		for ( ; i < N; i++ ) {
 			s += x[ ix ];
 			ix += strideX;
 		}

lib/node_modules/@stdlib/blas/ext/base/dssumpw/src/main.c

@@ -80,11 +80,11 @@ double API_SUFFIX(stdlib_strided_dssumpw_ndarray)( const CBLAS_INT N, const floa
 	if ( strideX == 0 ) {
 		return N * X[ 0 ];
 	}
-
 	if ( N < 8 ) {
 		// Use simple summation...
-		sum = 0.0;
-		for ( i = 0; i < N; i++ ) {
+		sum = (double)X[ ix ];
+		ix += strideX;
+		for ( i = 1; i < N; i++ ) {
 			sum += (double)X[ ix ];
 			ix += strideX;
 		}

lib/node_modules/@stdlib/blas/ext/base/dssumpw/test/test.ndarray.js

@@ -22,6 +22,7 @@
 
 var tape = require( 'tape' );
 var isnan = require( '@stdlib/math/base/assert/is-nan' );
+var isNegativeZero = require( '@stdlib/math/base/assert/is-negative-zero' );
 var Float32Array = require( '@stdlib/array/float32' );
 var dssumpw = require( './../lib/ndarray.js' );
 
@@ -74,6 +75,17 @@ tape( 'the function calculates the sum of all strided array elements', function
 	t.end();
 });
 
+tape( 'the function preserves the sign of zero', function test( t ) {
+	var x;
+	var v;
+
+	x = new Float32Array( [ -0.0, -0.0, -0.0, -0.0, -0.0 ] );
+	v = dssumpw( x.length, x, 1, 0 );
+	t.strictEqual( isNegativeZero( v ), true, 'returns expected value' );
+
+	t.end();
+});
+
 tape( 'if provided an `N` parameter less than or equal to `0`, the function returns `0.0`', function test( t ) {
 	var x;
 	var v;

lib/node_modules/@stdlib/blas/ext/base/dssumpw/test/test.ndarray.native.js

@@ -23,6 +23,7 @@
 var resolve = require( 'path' ).resolve;
 var tape = require( 'tape' );
 var isnan = require( '@stdlib/math/base/assert/is-nan' );
+var isNegativeZero = require( '@stdlib/math/base/assert/is-negative-zero' );
 var Float32Array = require( '@stdlib/array/float32' );
 var tryRequire = require( '@stdlib/utils/try-require' );
 
@@ -83,6 +84,17 @@ tape( 'the function calculates the sum of all strided array elements', opts, fun
 	t.end();
 });
 
+tape( 'the function preserves the sign of zero', opts, function test( t ) {
+	var x;
+	var v;
+
+	x = new Float32Array( [ -0.0, -0.0, -0.0, -0.0, -0.0 ] );
+	v = dssumpw( x.length, x, 1, 0 );
+	t.strictEqual( isNegativeZero( v ), true, 'returns expected value' );
+
+	t.end();
+});
+
 tape( 'if provided an `N` parameter less than or equal to `0`, the function returns `0.0`', opts, function test( t ) {
 	var x;
 	var v;