better power implementation

Objects/floatobject.c

@@ -316,20 +316,55 @@ float_divmod(v, w)
 	return mkvalue("(dd)", div, mod);
 }
 
+double powu(x, n)
+	double x;
+	long n;
+{
+	double r = 1.;
+	double p = x;
+	long mask = 1;
+	while (mask > 0 && n >= mask) {
+		if (n & mask)
+			r *= p;
+		mask <<= 1;
+		p *= p;
+	}
+	return r;
+}
+
+double powi(x, n)
+	double x;
+	long n;
+{
+	if (n > 10000 || n < -10000)
+		return pow(x, (double) n);
+	else if (n > 0)
+		return powu(x, n);
+	else
+		return 1./powu(x, -n);
+}
+
 static object *
 float_pow(v, w, z)
 	floatobject *v;
-	floatobject *w;
+	object *w;
 	floatobject *z;
 {
 	double iv, iw, ix;
-	iv = v->ob_fval;
+	long intw;
-	iw = w->ob_fval;
  /* XXX Doesn't handle overflows if z!=None yet; it may never do so :(
   * The z parameter is really only going to be useful for integers and
   * long integers.  Maybe something clever with logarithms could be done.
   * [AMK]
   */
+	iv = v->ob_fval;
+	iw = ((floatobject *)w)->ob_fval;
+	intw = (long)iw;
+	if (iw == intw) {
+		errno = 0;
+		ix = powi(iv, intw);
+	}
+	else {
 		/* Sort out special cases here instead of relying on pow() */
 		if (iw == 0.0) { 		/* x**0 is 1, even 0**0 */
 		 	if ((object *)z!=None) {
@@ -348,6 +383,7 @@ float_pow(v, w, z)
 		}
 		errno = 0;
 		ix = pow(iv, iw);
+	}
 	CHECK(ix);
 	if (errno != 0) {
 		/* XXX could it be another type of error? */