src/libm/s_cos.c
changeset 2756 a98604b691c8
child 3162 dc1eb82ffdaa
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/src/libm/s_cos.c	Mon Sep 15 06:33:23 2008 +0000
@@ -0,0 +1,90 @@
+/* @(#)s_cos.c 5.1 93/09/24 */
+/*
+ * ====================================================
+ * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
+ *
+ * Developed at SunPro, a Sun Microsystems, Inc. business.
+ * Permission to use, copy, modify, and distribute this
+ * software is freely granted, provided that this notice
+ * is preserved.
+ * ====================================================
+ */
+
+#if defined(LIBM_SCCS) && !defined(lint)
+static char rcsid[] = "$NetBSD: s_cos.c,v 1.7 1995/05/10 20:47:02 jtc Exp $";
+#endif
+
+/* cos(x)
+ * Return cosine function of x.
+ *
+ * kernel function:
+ *	__kernel_sin		... sine function on [-pi/4,pi/4]
+ *	__kernel_cos		... cosine function on [-pi/4,pi/4]
+ *	__ieee754_rem_pio2	... argument reduction routine
+ *
+ * Method.
+ *      Let S,C and T denote the sin, cos and tan respectively on
+ *	[-PI/4, +PI/4]. Reduce the argument x to y1+y2 = x-k*pi/2
+ *	in [-pi/4 , +pi/4], and let n = k mod 4.
+ *	We have
+ *
+ *          n        sin(x)      cos(x)        tan(x)
+ *     ----------------------------------------------------------
+ *	    0	       S	   C		 T
+ *	    1	       C	  -S		-1/T
+ *	    2	      -S	  -C		 T
+ *	    3	      -C	   S		-1/T
+ *     ----------------------------------------------------------
+ *
+ * Special cases:
+ *      Let trig be any of sin, cos, or tan.
+ *      trig(+-INF)  is NaN, with signals;
+ *      trig(NaN)    is that NaN;
+ *
+ * Accuracy:
+ *	TRIG(x) returns trig(x) nearly rounded
+ */
+
+#include "math.h"
+#include "math_private.h"
+
+libm_hidden_proto(cos)
+#ifdef __STDC__
+     double cos(double x)
+#else
+     double cos(x)
+     double x;
+#endif
+{
+    double y[2], z = 0.0;
+    int32_t n, ix;
+
+    /* High word of x. */
+    GET_HIGH_WORD(ix, x);
+
+    /* |x| ~< pi/4 */
+    ix &= 0x7fffffff;
+    if (ix <= 0x3fe921fb)
+        return __kernel_cos(x, z);
+
+    /* cos(Inf or NaN) is NaN */
+    else if (ix >= 0x7ff00000)
+        return x - x;
+
+    /* argument reduction needed */
+    else {
+        n = __ieee754_rem_pio2(x, y);
+        switch (n & 3) {
+        case 0:
+            return __kernel_cos(y[0], y[1]);
+        case 1:
+            return -__kernel_sin(y[0], y[1], 1);
+        case 2:
+            return -__kernel_cos(y[0], y[1]);
+        default:
+            return __kernel_sin(y[0], y[1], 1);
+        }
+    }
+}
+
+libm_hidden_def(cos)