fix: update implementation to preserve signed zeros

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---

Author: kgryte

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

@@ -20,7 +20,7 @@
 
 // MODULES //
 
-var float64ToFloat32 = require( '@stdlib/number/float64/base/to-float32' );
+var f32 = require( '@stdlib/number/float64/base/to-float32' );
 var absf = require( '@stdlib/math/base/special/absf' );
 
 
@@ -53,6 +53,7 @@ var absf = require( '@stdlib/math/base/special/absf' );
 */
 function ssumkbn( N, x, strideX, offsetX ) {
 	var sum;
+	var flg;
 	var ix;
 	var v;
 	var t;
@@ -64,22 +65,40 @@ function ssumkbn( N, x, strideX, offsetX ) {
 	}
 	ix = offsetX;
 	if ( strideX === 0 ) {
-		return float64ToFloat32( N * x[ ix ] );
+		return f32( N * x[ ix ] );
+	}
+	v = x[ ix ];
+	sum = v;
+
+	// 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 = 1; i < N; i++ ) {
+			v = x[ ix ];
+			if ( v !== 0.0 ) {
+				flg = true;
+				break;
+			}
+			sum = f32( sum + v );
+			ix += strideX;
+		}
+	} else {
+		flg = true;
+		ix += strideX;
+		i = 1;
 	}
-	sum = 0.0;
 	c = 0.0;
-	for ( i = 0; i < N; i++ ) {
+	for ( ; i < N; i++ ) {
 		v = x[ ix ];
-		t = float64ToFloat32( sum + v );
+		t = f32( sum + v );
 		if ( absf( sum ) >= absf( v ) ) {
-			c = float64ToFloat32( c + float64ToFloat32( float64ToFloat32( sum-t ) + v ) ); // eslint-disable-line max-len
+			c = f32( c + f32( f32( sum-t ) + v ) );
 		} else {
-			c = float64ToFloat32( c + float64ToFloat32( float64ToFloat32( v-t ) + sum ) ); // eslint-disable-line max-len
+			c = f32( c + f32( f32( v-t ) + sum ) );
 		}
 		sum = t;
 		ix += strideX;
 	}
-	return float64ToFloat32( sum + c );
+	return ( flg ) ? f32( sum+c ) : sum;
 }
 
 

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

@@ -66,6 +66,7 @@ float API_SUFFIX(stdlib_strided_ssumkbn_ndarray)( const CBLAS_INT N, const float
 	float v;
 	float t;
 	float c;
+	int flg;
 
 	if ( N <= 0 ) {
 		return 0.0f;
@@ -74,9 +75,28 @@ float API_SUFFIX(stdlib_strided_ssumkbn_ndarray)( const CBLAS_INT N, const float
 	if ( strideX == 0 ) {
 		return N * X[ ix ];
 	}
-	sum = 0.0f;
+	v = X[ ix ];
+	sum = v;
+	flg = 0;
+
+	// In order to preserve the sign of zero which can be lost during compensated summation below, find the first non-zero element...
+	if ( sum == 0.0f ) {
+		for ( i = 1; i < N; i++ ) {
+			v = X[ ix ];
+			if ( v != 0.0f ) {
+				flg = 1;
+				break;
+			}
+			sum += v;
+			ix += strideX;
+		}
+	} else {
+		flg = 1;
+		ix += strideX;
+		i = 1;
+	}
 	c = 0.0f;
-	for ( i = 0; i < N; i++ ) {
+	for ( ; i < N; i++ ) {
 		v = X[ ix ];
 		t = sum + v;
 		if ( stdlib_base_absf( sum ) >= stdlib_base_absf( v ) ) {
@@ -87,5 +107,5 @@ float API_SUFFIX(stdlib_strided_ssumkbn_ndarray)( const CBLAS_INT N, const float
 		sum = t;
 		ix += strideX;
 	}
-	return sum + c;
+	return ( flg == 1 ) ? sum+c : sum;
 }

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

@@ -22,6 +22,7 @@
 
 var tape = require( 'tape' );
 var isPositiveZerof = require( '@stdlib/math/base/assert/is-positive-zerof' );
+var isNegativeZerof = require( '@stdlib/math/base/assert/is-negative-zerof' );
 var isnanf = require( '@stdlib/math/base/assert/is-nanf' );
 var Float32Array = require( '@stdlib/array/float32' );
 var ssumkbn = require( './../lib/ndarray.js' );
@@ -67,14 +68,14 @@ tape( 'the function calculates the sum of all strided array elements', function
 	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 Float32Array( [ -0.0, -0.0, -0.0 ] );
 
 	v = ssumkbn( x.length, x, 1, 0 );
-	t.strictEqual( isPositiveZerof( v ), true, 'returns expected value' );
+	t.strictEqual( isNegativeZerof( v ), true, 'returns expected value' );
 
 	x = new Float32Array( [ 0.0, -0.0, -0.0 ] );
 

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

@@ -23,6 +23,7 @@
 var resolve = require( 'path' ).resolve;
 var tape = require( 'tape' );
 var isPositiveZerof = require( '@stdlib/math/base/assert/is-positive-zerof' );
+var isNegativeZerof = require( '@stdlib/math/base/assert/is-negative-zerof' );
 var isnanf = require( '@stdlib/math/base/assert/is-nanf' );
 var Float32Array = require( '@stdlib/array/float32' );
 var tryRequire = require( '@stdlib/utils/try-require' );
@@ -76,14 +77,14 @@ tape( 'the function calculates the sum of all strided array elements', opts, fun
 	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 Float32Array( [ -0.0, -0.0, -0.0 ] );
 
 	v = ssumkbn( x.length, x, 1, 0 );
-	t.strictEqual( isPositiveZerof( v ), true, 'returns expected value' );
+	t.strictEqual( isNegativeZerof( v ), true, 'returns expected value' );
 
 	x = new Float32Array( [ 0.0, -0.0, -0.0 ] );