refactor: add explicit NaN check

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---

Author: kgryte

lib/node_modules/@stdlib/math/base/special/factorial2f/manifest.json

@@ -40,7 +40,8 @@
         "@stdlib/math/base/assert/is-evenf",
         "@stdlib/constants/float32/pinf",
         "@stdlib/constants/float32/max-nth-double-factorial",
-        "@stdlib/math/base/assert/is-nonnegative-integerf"
+        "@stdlib/math/base/assert/is-nonnegative-integerf",
+        "@stdlib/math/base/assert/is-nanf"
       ]
     },
     {
@@ -57,7 +58,8 @@
         "@stdlib/math/base/assert/is-evenf",
         "@stdlib/constants/float32/pinf",
         "@stdlib/constants/float32/max-nth-double-factorial",
-        "@stdlib/math/base/assert/is-nonnegative-integerf"
+        "@stdlib/math/base/assert/is-nonnegative-integerf",
+        "@stdlib/math/base/assert/is-nanf"
       ]
     },
     {
@@ -74,7 +76,8 @@
         "@stdlib/math/base/assert/is-evenf",
         "@stdlib/constants/float32/pinf",
         "@stdlib/constants/float32/max-nth-double-factorial",
-        "@stdlib/math/base/assert/is-nonnegative-integerf"
+        "@stdlib/math/base/assert/is-nonnegative-integerf",
+        "@stdlib/math/base/assert/is-nanf"
       ]
     }
   ]

lib/node_modules/@stdlib/math/base/special/factorial2f/src/main.c

@@ -18,6 +18,7 @@
 
 #include "stdlib/math/base/special/factorial2f.h"
 #include "stdlib/math/base/assert/is_evenf.h"
+#include "stdlib/math/base/assert/is_nanf.h"
 #include "stdlib/constants/float32/pinf.h"
 #include "stdlib/constants/float32/max_nth_double_factorial.h"
 #include "stdlib/math/base/assert/is_nonnegative_integerf.h"
@@ -37,7 +38,7 @@ float stdlib_base_factorial2f( const float n ) {
 	float out;
 	float i;
 
-	if ( !stdlib_base_is_nonnegative_integerf( n ) ) {
+	if ( stdlib_base_is_nanf( n ) || !stdlib_base_is_nonnegative_integerf( n ) ) {
 		return 0.0f / 0.0f; // NaN
 	}
 	if ( n > STDLIB_CONSTANT_FLOAT32_MAX_NTH_DOUBLE_FACTORIAL ) {

lib/node_modules/@stdlib/math/base/special/factorial2f/test/test.native.js

@@ -26,6 +26,7 @@ var isnanf = require( '@stdlib/math/base/assert/is-nanf' );
 var absf = require( '@stdlib/math/base/special/absf' );
 var incrspace = require( '@stdlib/array/base/incrspace' );
 var PINF = require( '@stdlib/constants/float32/pinf' );
+var NINF = require( '@stdlib/constants/float32/ninf' );
 var EPS = require( '@stdlib/constants/float32/eps' );
 var tryRequire = require( '@stdlib/utils/try-require' );
 
@@ -64,6 +65,24 @@ tape( 'if provided a negative integer, the function returns `NaN`', opts, functi
 	t.end();
 });
 
+tape( 'if provided negative infinity, the function returns `NaN`', opts, function test( t ) {
+	var v = factorial2f( NINF );
+	t.strictEqual( isnanf( v ), true, 'returns expected value' );
+	t.end();
+});
+
+tape( 'if provided positive infinity, the function returns `+infinity`', opts, function test( t ) {
+	var v = factorial2f( PINF );
+	t.strictEqual( v, PINF, 'returns expected value' );
+	t.end();
+});
+
+tape( 'if provided `NaN`, the function returns `NaN`', opts, function test( t ) {
+	var v = factorial2f( NaN );
+	t.strictEqual( isnanf( v ), true, 'returns expected value' );
+	t.end();
+});
+
 tape( 'the function evaluates the double factorial', opts, function test( t ) {
 	var expected;
 	var delta;