20060303a

1 files changed, 53 insertions, 0 deletions

diff --git a/libkern/sqrt.c b/libkern/sqrt.c
new file mode 100644
index 00000000..0d235126
--- /dev/null
+++ b/libkern/sqrt.c
@@ -0,0 +1,53 @@
+/*
+	sqrt returns the square root of its floating
+	point argument. Newton's method.
+
+	calls frexp
+*/
+
+#include <lib9.h>
+
+double
+sqrt(double arg)
+{
+	double x, temp;
+	int exp, i;
+
+	if(arg <= 0) {
+		if(arg < 0)
+			return NaN();
+		return 0;
+	}
+	if(isInf(arg, 1))
+		return arg;
+	x = frexp(arg, &exp);
+	while(x < 0.5) {
+		x *= 2;
+		exp--;
+	}
+	/*
+	 * NOTE
+	 * this wont work on 1's comp
+	 */
+	if(exp & 1) {
+		x *= 2;
+		exp--;
+	}
+	temp = 0.5 * (1.0+x);
+
+	while(exp > 60) {
+		temp *= (1L<<30);
+		exp -= 60;
+	}
+	while(exp < -60) {
+		temp /= (1L<<30);
+		exp += 60;
+	}
+	if(exp >= 0)
+		temp *= 1L << (exp/2);
+	else
+		temp /= 1L << (-exp/2);
+	for(i=0; i<=4; i++)
+		temp = 0.5*(temp + arg/temp);
+	return temp;
+}