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authorUlrich Drepper <drepper@redhat.com>1999-07-14 00:54:57 +0000
committerUlrich Drepper <drepper@redhat.com>1999-07-14 00:54:57 +0000
commitabfbdde177c3a7155070dda1b2cdc8292054cc26 (patch)
treee021306b596381fbf8311d2b7eb294e918ff17c8 /sysdeps/ieee754/ldbl-96/e_hypotl.c
parent86421aa57ecfd70963ae66848bd6a6dd3b8e0fe6 (diff)
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+/* e_hypotl.c -- long double version of e_hypot.c.
+ * Conversion to long double by Ulrich Drepper,
+ * Cygnus Support, drepper@cygnus.com.
+ */
+
+/*
+ * ====================================================
+ * 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: $";
+#endif
+
+/* __ieee754_hypotl(x,y)
+ *
+ * Method :
+ *	If (assume round-to-nearest) z=x*x+y*y
+ *	has error less than sqrt(2)/2 ulp, than
+ *	sqrt(z) has error less than 1 ulp (exercise).
+ *
+ *	So, compute sqrt(x*x+y*y) with some care as
+ *	follows to get the error below 1 ulp:
+ *
+ *	Assume x>y>0;
+ *	(if possible, set rounding to round-to-nearest)
+ *	1. if x > 2y  use
+ *		x1*x1+(y*y+(x2*(x+x1))) for x*x+y*y
+ *	where x1 = x with lower 32 bits cleared, x2 = x-x1; else
+ *	2. if x <= 2y use
+ *		t1*y1+((x-y)*(x-y)+(t1*y2+t2*y))
+ *	where t1 = 2x with lower 32 bits cleared, t2 = 2x-t1,
+ *	y1= y with lower 32 bits chopped, y2 = y-y1.
+ *
+ *	NOTE: scaling may be necessary if some argument is too
+ *	      large or too tiny
+ *
+ * Special cases:
+ *	hypot(x,y) is INF if x or y is +INF or -INF; else
+ *	hypot(x,y) is NAN if x or y is NAN.
+ *
+ * Accuracy:
+ * 	hypot(x,y) returns sqrt(x^2+y^2) with error less
+ * 	than 1 ulps (units in the last place)
+ */
+
+#include "math.h"
+#include "math_private.h"
+
+#ifdef __STDC__
+	long double __ieee754_hypotl(long double x, long double y)
+#else
+	long double __ieee754_hypotl(x,y)
+	long double x, y;
+#endif
+{
+	long double a,b,t1,t2,y1,y2,w;
+	u_int32_t j,k,ea,eb;
+
+	GET_LDOUBLE_EXP(ea,x);
+	ea &= 0x7fff;
+	GET_LDOUBLE_EXP(eb,y);
+	eb &= 0x7fff;
+	if(eb > ea) {a=y;b=x;j=ea; ea=eb;eb=j;} else {a=x;b=y;}
+	SET_LDOUBLE_EXP(a,ea);	/* a <- |a| */
+	SET_LDOUBLE_EXP(b,eb);	/* b <- |b| */
+	if((ea-eb)>0x46) {return a+b;} /* x/y > 2**70 */
+	k=0;
+	if(ea > 0x5f3f) {	/* a>2**8000 */
+	   if(ea == 0x7fff) {	/* Inf or NaN */
+	       u_int32_t exp,high,low;
+	       w = a+b;			/* for sNaN */
+	       GET_LDOUBLE_WORDS(exp,high,low,a);
+	       if(((high&0x7fffffff)|low)==0) w = a;
+	       GET_LDOUBLE_WORDS(exp,high,low,b);
+	       if(((eb^0x7fff)|(high&0x7fffffff)|low)==0) w = b;
+	       return w;
+	   }
+	   /* scale a and b by 2**-9600 */
+	   ea -= 0x2580; eb -= 0x2580;	k += 9600;
+	   SET_LDOUBLE_EXP(a,ea);
+	   SET_LDOUBLE_EXP(b,eb);
+	}
+	if(eb < 0x20bf) {	/* b < 2**-8000 */
+	    if(eb == 0) {	/* subnormal b or 0 */
+	        u_int32_t exp,high,low;
+		GET_LDOUBLE_WORDS(exp,high,low,b);
+		if((high|low)==0) return a;
+		SET_LDOUBLE_WORDS(t1, 0x7ffd, 0, 0);	/* t1=2^16382 */
+		b *= t1;
+		a *= t1;
+		k -= 16382;
+	    } else {		/* scale a and b by 2^9600 */
+	        ea += 0x2580; 	/* a *= 2^9600 */
+		eb += 0x2580;	/* b *= 2^9600 */
+		k -= 9600;
+		SET_LDOUBLE_EXP(a,ea);
+		SET_LDOUBLE_EXP(b,eb);
+	    }
+	}
+    /* medium size a and b */
+	w = a-b;
+	if (w>b) {
+	    u_int32_t high;
+	    GET_LDOUBLE_MSW(high,a);
+	    SET_LDOUBLE_WORDS(t1,ea,high,0);
+	    t2 = a-t1;
+	    w  = __ieee754_sqrtl(t1*t1-(b*(-b)-t2*(a+t1)));
+	} else {
+	    u_int32_t high;
+	    GET_LDOUBLE_MSW(high,b);
+	    a  = a+a;
+	    SET_LDOUBLE_WORDS(y1,eb,high,0);
+	    y2 = b - y1;
+	    GET_LDOUBLE_MSW(high,a);
+	    SET_LDOUBLE_WORDS(t1,ea+1,high,0);
+	    t2 = a - t1;
+	    w  = __ieee754_sqrtl(t1*y1-(w*(-w)-(t1*y2+t2*b)));
+	}
+	if(k!=0) {
+	    u_int32_t exp;
+	    t1 = 1.0;
+	    GET_LDOUBLE_EXP(exp,t1);
+	    SET_LDOUBLE_EXP(t1,exp+k);
+	    return t1*w;
+	} else return w;
+}