rename libc to libjehanne; improve libposix

This is to avoid conflicts between standards' assumptions and Jehanne's choices

sys/src/lib/jehanne/port/hypot.c

@@ -0,0 +1,50 @@
+/*
+ * This file is part of the UCB release of Plan 9. It is subject to the license
+ * terms in the LICENSE file found in the top-level directory of this
+ * distribution and at http://akaros.cs.berkeley.edu/files/Plan9License. No
+ * part of the UCB release of Plan 9, including this file, may be copied,
+ * modified, propagated, or distributed except according to the terms contained
+ * in the LICENSE file.
+ */
+
+/*
+ * hypot -- jehanne_sqrt(p*p+q*q), but overflows only if the result does.
+ * See Cleve Moler and Donald Morrison,
+ * ``Replacing Square Roots by Pythagorean Sums,''
+ * IBM Journal of Research and Development,
+ * Vol. 27, Number 6, pp. 577-581, Nov. 1983
+ */
+
+#include <u.h>
+#include <libc.h>
+
+double
+jehanne_hypot(double p, double q)
+{
+	double r, s, pfac;
+
+	if(p < 0)
+		p = -p;
+	if(q < 0)
+		q = -q;
+	if(p < q) {
+		r = p;
+		p = q;
+		q = r;
+	}
+	if(p == 0)
+		return 0;
+	pfac = p;
+	r = q = q/p;
+	p = 1;
+	for(;;) {
+		r *= r;
+		s = r+4;
+		if(s == 4)
+			return p*pfac;
+		r /= s;
+		p += 2*r*p;
+		q *= r;
+		r = q/p;
+	}
+}