Merge a bugfix from FDLIBM 5.3 to ensure that the error in tan()

is always less than 1 ulp.  Also update to the 5.3 license.

Obtained from:	FDLIBM

1 files changed, 24 insertions, 10 deletions

diff --git a/lib/msun/src/k_tan.c b/lib/msun/src/k_tan.c
index bb7770d..b7cdf35 100644
--- a/lib/msun/src/k_tan.c
+++ b/lib/msun/src/k_tan.c
@@ -1,9 +1,8 @@
 /* @(#)k_tan.c 5.1 93/09/24 */
 /*
  * ====================================================
- * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
+ * Copyright 2004 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.
@@ -77,14 +76,29 @@ __kernel_tan(double x, double y, int iy)
 	int32_t ix,hx;
 	GET_HIGH_WORD(hx,x);
 	ix = hx&0x7fffffff;	/* high word of |x| */
-	if(ix<0x3e300000)			/* x < 2**-28 */
-	    {if((int)x==0) {			/* generate inexact */
-	        u_int32_t low;
-		GET_LOW_WORD(low,x);
-		if(((ix|low)|(iy+1))==0) return one/fabs(x);
-		else return (iy==1)? x: -one/x;
-	    }
-	    }
+	if(ix<0x3e300000) {			/* x < 2**-28 */
+		if ((int) x == 0) {		/* generate inexact */
+			u_int32_t low;
+			GET_LOW_WORD(low,x);
+			if (((ix | low) | (iy + 1)) == 0)
+				return one / fabs(x);
+			else {
+				if (iy == 1)
+					return x;
+				else {	/* compute -1 / (x+y) carefully */
+					double a, t;
+
+					z = w = x + y;
+					SET_LOW_WORD(z, 0);
+					v = y - (z - x);
+					t = a = -one / w;
+					SET_LOW_WORD(t, 0);
+					s = one + t * z;
+					return t + a * (s + t * v);
+				}
+			}
+		}
+	}
 	if(ix>=0x3FE59428) { 			/* |x|>=0.6744 */
 	    if(hx<0) {x = -x; y = -y;}
 	    z = pio4-x;