fix: update the function according to reference implementation

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Author: anandkaranubc

lib/node_modules/@stdlib/math/base/special/cosd/lib/main.js

@@ -20,10 +20,13 @@
 
 // MODULES //
 
-var cos = require( '@stdlib/math/base/special/cos' );
 var deg2rad = require( '@stdlib/math/base/special/deg2rad' );
-var isInteger = require( '@stdlib/math/base/assert/is-integer' );
-var isInfinite = require( '@stdlib/assert/is-infinite' );
+var kernelSin = require( '@stdlib/math/base/special/kernel-sin' );
+var kernelCos = require( '@stdlib/math/base/special/kernel-cos' );
+var fmod = require( '@stdlib/math/base/special/fmod' );
+var abs = require( '@stdlib/math/base/special/abs' );
+var isnan = require( '@stdlib/math/base/assert/is-nan' );
+var isInfinite = require( '@stdlib/math/base/assert/is-infinite' );
 
 
 // MAIN //
@@ -52,18 +55,35 @@ var isInfinite = require( '@stdlib/assert/is-infinite' );
 */
 function cosd( x ) {
 	var xRad;
+	var rx;
 
-	if ( isInfinite( x ) ) {
+	if (
+		isInfinite( x ) ||
+		isnan( x )
+	) {
 		return NaN;
 	}
 
-	if ( isInteger( ( ( x / 90.0 ) - 1.0 ) / 2.0 ) ) {
-		return 0.0;
-	}
-
-	xRad = deg2rad( x );
+	rx = abs( fmod( x, 360.0 ) );
 
-	return cos( xRad );
+	if ( rx <= 45.0 ) {
+		xRad = deg2rad( rx );
+		return kernelCos( xRad, 0.0 );
+	}
+	if ( rx < 135.0 ) {
+		xRad = deg2rad( 90.0-rx );
+		return kernelSin( xRad, 0.0 );
+	}
+	if ( rx <= 225.0 ) {
+		xRad = deg2rad( 180.0-rx );
+		return -kernelCos( xRad, 0.0 );
+	}
+	if ( rx < 315.0 ) {
+		xRad = deg2rad( rx-270.0 );
+		return kernelSin( xRad, 0.0 );
+	}
+	xRad = deg2rad( 360.0-rx );
+	return kernelCos( xRad, 0.0 );
 }
 
 

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

@@ -37,10 +37,13 @@
       "libpath": [],
       "dependencies": [
         "@stdlib/math/base/napi/unary",
-        "@stdlib/math/base/assert/is-integer",
+        "@stdlib/math/base/assert/is-nan",
         "@stdlib/math/base/assert/is-infinite",
         "@stdlib/math/base/special/deg2rad",
-        "@stdlib/math/base/special/cos"
+        "@stdlib/math/base/special/kernel-sin",
+        "@stdlib/math/base/special/kernel-cos",
+        "@stdlib/math/base/special/abs",
+        "@stdlib/math/base/special/fmod"
       ]
     },
     {
@@ -54,10 +57,13 @@
       "libraries": [],
       "libpath": [],
       "dependencies": [
-        "@stdlib/math/base/assert/is-integer",
+        "@stdlib/math/base/assert/is-nan",
         "@stdlib/math/base/assert/is-infinite",
         "@stdlib/math/base/special/deg2rad",
-        "@stdlib/math/base/special/cos"
+        "@stdlib/math/base/special/kernel-sin",
+        "@stdlib/math/base/special/kernel-cos",
+        "@stdlib/math/base/special/abs",
+        "@stdlib/math/base/special/fmod"
       ]
     },
     {
@@ -71,10 +77,13 @@
       "libraries": [],
       "libpath": [],
       "dependencies": [
-        "@stdlib/math/base/assert/is-integer",
+        "@stdlib/math/base/assert/is-nan",
         "@stdlib/math/base/assert/is-infinite",
         "@stdlib/math/base/special/deg2rad",
-        "@stdlib/math/base/special/cos"
+        "@stdlib/math/base/special/kernel-sin",
+        "@stdlib/math/base/special/kernel-cos",
+        "@stdlib/math/base/special/abs",
+        "@stdlib/math/base/special/fmod"
       ]
     }
   ]

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

@@ -17,9 +17,12 @@
 */
 
 #include "stdlib/math/base/special/cosd.h"
-#include "stdlib/math/base/special/cos.h"
+#include "stdlib/math/base/special/kernel_sin.h"
+#include "stdlib/math/base/special/kernel_cos.h"
 #include "stdlib/math/base/special/deg2rad.h"
-#include "stdlib/math/base/assert/is_integer.h"
+#include "stdlib/math/base/special/abs.h"
+#include "stdlib/math/base/special/fmod.h"
+#include "stdlib/math/base/assert/is_nan.h"
 #include "stdlib/math/base/assert/is_infinite.h"
 
 /**
@@ -34,12 +37,30 @@
 */
 double stdlib_base_cosd( const double x ) {
 	double xRad;
-	if ( stdlib_base_is_infinite( x ) ) {
+	double rx;
+
+	if ( stdlib_base_is_infinite( x ) || stdlib_base_is_nan( x ) ) {
 		return 0.0 / 0.0; // NaN
 	}
-	if ( stdlib_base_is_integer( ( ( x / 90.0 ) - 1.0 ) / 2.0 ) ) {
-		return 0.0;
+
+	rx = stdlib_base_abs( stdlib_base_fmod( x, 360.0 ) );
+
+	if ( rx <= 45.0 ) {
+		xRad = stdlib_base_deg2rad( rx );
+		return stdlib_base_kernel_cos( xRad, 0.0 );
+	}
+	if ( rx < 135.0 ) {
+		xRad = stdlib_base_deg2rad( 90.0-rx );
+		return stdlib_base_kernel_sin( xRad, 0.0 );
+	}
+	if ( rx <= 225.0 ) {
+		xRad = stdlib_base_deg2rad( 180.0-rx );
+		return -stdlib_base_kernel_cos( xRad, 0.0 );
+	}
+	if ( rx < 315.0 ) {
+		xRad = stdlib_base_deg2rad( rx-270.0 );
+		return stdlib_base_kernel_sin( xRad, 0.0 );
 	}
-	xRad = stdlib_base_deg2rad( x );
-	return stdlib_base_cos( xRad );
+	xRad = stdlib_base_deg2rad( 360.0-rx );
+	return stdlib_base_kernel_cos( xRad, 0.0 );
 }