fix: address pointer increment bug

---
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---

Author: kgryte

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

@@ -53,25 +53,57 @@ var abs = require( '@stdlib/math/base/special/abs' );
 */
 function dnansumkbn( N, x, strideX, offsetX ) {
 	var sum;
+	var flg;
 	var ix;
 	var v;
 	var t;
 	var c;
 	var i;
 
-	sum = 0.0;
 	if ( N <= 0 ) {
-		return sum;
+		return 0.0;
 	}
 	ix = offsetX;
 	if ( strideX === 0 ) {
 		if ( isnan( x[ ix ] ) ) {
-			return sum;
+			return 0.0;
 		}
 		return x[ ix ] * N;
 	}
-	c = 0.0;
+	// Find the first non-NaN element...
 	for ( i = 0; i < N; i++ ) {
+		v = x[ ix ];
+		if ( isnan( v ) === false ) {
+			break;
+		}
+		ix += strideX;
+	}
+	if ( i === N ) {
+		return NaN;
+	}
+	sum = v;
+	ix += strideX;
+	flg = 0;
+	i += 1;
+
+	// In order to preserve the sign of zero which can be lost during compensated summation below, find the first non-zero element...
+	if ( sum === 0.0 ) {
+		for ( ; i < N; i++ ) {
+			v = x[ ix ];
+			if ( isnan( v ) === false ) {
+				if ( v !== 0.0 ) {
+					flg = 1;
+					break;
+				}
+				sum += v;
+			}
+			ix += strideX;
+		}
+	} else {
+		flg = 1;
+	}
+	c = 0.0;
+	for ( ; i < N; i++ ) {
 		v = x[ ix ];
 		if ( isnan( v ) === false ) {
 			t = sum + v;
@@ -84,7 +116,7 @@ function dnansumkbn( N, x, strideX, offsetX ) {
 		}
 		ix += strideX;
 	}
-	return sum + c;
+	return ( flg ) ? sum+c : sum;
 }
 
 

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

@@ -22,6 +22,7 @@
 
 var tape = require( 'tape' );
 var isPositiveZero = require( '@stdlib/math/base/assert/is-positive-zero' );
+var isNegativeZero = require( '@stdlib/math/base/assert/is-negative-zero' );
 var Float64Array = require( '@stdlib/array/float64' );
 var dnansumkbn = require( './../lib/ndarray.js' );
 
@@ -78,14 +79,14 @@ tape( 'the function calculates the sum of strided array elements (ignoring NaN v
 	t.end();
 });
 
-tape( 'the function does not preserve the sign of zero', function test( t ) {
+tape( 'the function preserves the sign of zero', function test( t ) {
 	var x;
 	var v;
 
 	x = new Float64Array( [ -0.0, -0.0, -0.0 ] );
 
 	v = dnansumkbn( x.length, x, 1, 0 );
-	t.strictEqual( isPositiveZero( v ), true, 'returns expected value' );
+	t.strictEqual( isNegativeZero( v ), true, 'returns expected value' );
 
 	x = new Float64Array( [ 0.0, -0.0, -0.0 ] );
 

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

@@ -23,6 +23,7 @@
 var resolve = require( 'path' ).resolve;
 var tape = require( 'tape' );
 var isPositiveZero = require( '@stdlib/math/base/assert/is-positive-zero' );
+var isNegativeZero = require( '@stdlib/math/base/assert/is-negative-zero' );
 var Float64Array = require( '@stdlib/array/float64' );
 var tryRequire = require( '@stdlib/utils/try-require' );
 
@@ -87,14 +88,14 @@ tape( 'the function calculates the sum of strided array elements (ignoring NaN v
 	t.end();
 });
 
-tape( 'the function does not preserve the sign of zero', opts, function test( t ) {
+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 ] );
 
 	v = dnansumkbn( x.length, x, 1, 0 );
-	t.strictEqual( isPositiveZero( v ), true, 'returns expected value' );
+	t.strictEqual( isNegativeZero( v ), true, 'returns expected value' );
 
 	x = new Float64Array( [ 0.0, -0.0, -0.0 ] );