refactor: use ndarray utility to normalize an index

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---

Author: kgryte

lib/node_modules/@stdlib/ndarray/base/expand-dimensions/lib/main.js

@@ -21,6 +21,7 @@
 // MODULES //
 
 var isReadOnly = require( '@stdlib/ndarray/base/assert/is-read-only' );
+var normalizeIndex = require( '@stdlib/ndarray/base/normalize-index' );
 var getDType = require( '@stdlib/ndarray/base/dtype' );
 var getShape = require( '@stdlib/ndarray/base/shape' );
 var getStrides = require( '@stdlib/ndarray/base/strides' );
@@ -77,6 +78,7 @@ function expandDimensions( x, axis ) {
 	var ord;
 	var sh;
 	var st;
+	var d;
 	var N;
 	var i;
 
@@ -88,15 +90,11 @@ function expandDimensions( x, axis ) {
 	strides = [];
 	shape = [];
 
-	if ( axis < 0 ) {
-		if ( axis < -N-1 ) {
-			throw new RangeError( format( 'invalid argument. Specified axis is out-of-bounds. Must be on the interval: [-%u-1, %u]. Value: `%d`.', N, N, axis ) );
-		}
-		axis += N + 1;
-	} else if ( axis > N ) {
-		throw new RangeError( format( 'invalid argument. Specified axis is out-of-bounds. Must be on the interval: [-%u-1, %u]. Value: `%d`.', N, N, axis ) );
+	d = normalizeIndex( axis, N );
+	if ( d === -1 ) {
+		throw new RangeError( format( 'invalid argument. Specified axis is out-of-bounds. Must be on the interval: [-%u, %u]. Value: `%d`.', N+1, N, axis ) );
 	}
-	if ( axis === 0 ) {
+	if ( d === 0 ) {
 		// Prepend singleton dimension...
 		shape.push( 1 );
 		strides.push( st[ 0 ] );
@@ -106,7 +104,7 @@ function expandDimensions( x, axis ) {
 			shape.push( sh[ i ] );
 			strides.push( st[ i ] );
 		}
-	} else if ( axis === N ) {
+	} else if ( d === N ) {
 		// Copy dimensions...
 		for ( i = 0; i < N; i++ ) {
 			shape.push( sh[ i ] );
@@ -118,17 +116,17 @@ function expandDimensions( x, axis ) {
 	} else {
 		// Insert a singleton dimension...
 		for ( i = 0; i < N+1; i++ ) {
-			if ( i === axis ) {
+			if ( i === d ) {
 				shape.push( 1 );
 				if ( ord === 'row-major' ) {
 					strides.push( st[ i-1 ] );
 				} else { // ord === 'column-major'
 					strides.push( st[ i ] );
 				}
-			} else if ( i < axis ) {
+			} else if ( i < d ) {
 				shape.push( sh[ i ] );
 				strides.push( st[ i ] );
-			} else { // i > axis
+			} else { // i > d
 				shape.push( sh[ i-1 ] );
 				strides.push( st[ i-1 ] );
 			}