chore: adding case for x < 0.0

Author: Neerajpathak07

lib/node_modules/@stdlib/math/base/special/atanh/src/main.c

@@ -95,25 +95,31 @@ double stdlib_base_atanh( const double x ) {
 	// Split `x` into high and low words:
 	stdlib_base_float64_to_words( x, &hx, &lx );
 
-	ax = x;
 	ahx = hx & STDLIB_CONSTANT_FLOAT64_HIGH_WORD_ABS_MASK;
 
 	// special cases
-	if ( ax == 1.0 ) {
+	if ( x == 1.0 ) {
 		return STDLIB_CONSTANT_FLOAT64_PINF;
 	}
-	if ( ax == -1.0 ) {
+	if ( x == -1.0 ) {
 		return STDLIB_CONSTANT_FLOAT64_NINF;
 	}
 
+	if ( x < 0.0 ) {
+		hx = 1;
+		ax = -x;
+	} else {
+		hx = 0;
+		ax = x;
+	}
 	// Case: |x| < 2**-28
 	if ( ax < NEAR_ZERO ) {
 		return ( hx == 1 ) ? -ax : ax;
 	}
 
 	stdlib_base_float64_set_high_word( ahx, &ax );
 
-	if( ahx < 0.5 ) {
+	if( ax < 0.5 ) {
 		t = ax + ax;
 		t = 0.5 * stdlib_base_log1p( t + ( t * ax / ( 1.0 - ax ) ) );
 	} else {