fix: update implementation to preserve signed zeros

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---

Author: kgryte

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

@@ -48,18 +48,19 @@ function dsumors( N, x, strideX, offsetX ) {
 	var m;
 	var i;
 
-	sum = 0.0;
 	if ( N <= 0 ) {
-		return sum;
+		return 0.0;
 	}
 	ix = offsetX;
 	if ( strideX === 0 ) {
 		return N * x[ ix ];
 	}
+	sum = x[ ix ];
+	ix += strideX;
 
 	// If the stride is equal to `1`, use unrolled loops...
 	if ( strideX === 1 ) {
-		m = N % M;
+		m = (N-1) % M;
 
 		// If we have a remainder, run a clean-up loop...
 		if ( m > 0 ) {
@@ -71,13 +72,13 @@ function dsumors( N, x, strideX, offsetX ) {
 		if ( N < M ) {
 			return sum;
 		}
-		for ( i = m; i < N; i += M ) {
+		for ( i = m; i < N-1; i += M ) {
 			sum += x[ix] + x[ix+1] + x[ix+2] + x[ix+3] + x[ix+4] + x[ix+5];
 			ix += M;
 		}
 		return sum;
 	}
-	for ( i = 0; i < N; i++ ) {
+	for ( i = 1; i < N; i++ ) {
 		sum += x[ ix ];
 		ix += strideX;
 	}

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

@@ -48,17 +48,19 @@ double API_SUFFIX(stdlib_strided_dsumors_ndarray)( const CBLAS_INT N, const doub
 	CBLAS_INT i;
 	double sum;
 
-	sum = 0.0;
 	if ( N <= 0 ) {
-		return sum;
+		return 0.0;
 	}
 	ix = offsetX;
 	if ( strideX == 0 ) {
 		return N * X[ ix ];
 	}
+	sum = X[ ix ];
+	ix += strideX;
+
 	// If the stride is equal to `1`, use unrolled loops...
 	if ( strideX == 1 ) {
-		m = N % 6;
+		m = (N-1) % 6;
 
 		// If we have a remainder, run a clean-up loop...
 		if ( m > 0 ) {
@@ -69,12 +71,12 @@ double API_SUFFIX(stdlib_strided_dsumors_ndarray)( const CBLAS_INT N, const doub
 		if ( N < 6 ) {
 			return sum;
 		}
-		for ( i = m; i < N; i += 6 ) {
+		for ( i = m; i < N-1; i += 6 ) {
 			sum += X[i] + X[i+1] + X[i+2] + X[i+3] + X[i+4] + X[i+5];
 		}
 		return sum;
 	}
-	for ( i = 0; i < N; i++ ) {
+	for ( i = 1; i < N; i++ ) {
 		sum += X[ ix ];
 		ix += strideX;
 	}

lib/node_modules/@stdlib/blas/ext/base/dsumors/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 Float64Array = require( '@stdlib/array/float64' );
 var dsumors = require( './../lib/ndarray.js' );
 
@@ -66,6 +67,17 @@ 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 Float64Array( [ -0.0, -0.0, -0.0, -0.0, -0.0 ] );
+	v = dsumors( 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/dsumors/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 Float64Array = require( '@stdlib/array/float64' );
 var tryRequire = require( '@stdlib/utils/try-require' );
 
@@ -75,6 +76,17 @@ 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 Float64Array( [ -0.0, -0.0, -0.0, -0.0, -0.0 ] );
+	v = dsumors( 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;