SF bug 115831 and Ping's SF patch 101751, 0.0**-2.0 returns inf rather than

raise ValueError.  Checked in the patch as far as it went, but also changed
all of ints, longs and floats to raise ZeroDivisionError instead when raising
0 to a negative number.  This is what 754-inspired stds require, as the "true
result" is an infinity obtained from finite operands, i.e. it's a singularity.
Also changed float pow to not be so timid about using its square-and-multiply
algorithm.  Note that what math.pow does is unrelated to what builtin pow
does, and will still vary by platform.

3 files changed, 47 insertions, 32 deletions

diff --git a/Objects/floatobject.c b/Objects/floatobject.c
index 17f70b2..d776147 100644
--- a/Objects/floatobject.c
+++ b/Objects/floatobject.c
@@ -449,20 +449,33 @@ float_pow(PyFloatObject *v, PyObject *w, PyFloatObject *z)
 	iv = v->ob_fval;
 	iw = ((PyFloatObject *)w)->ob_fval;
 	intw = (long)iw;
-	if (iw == intw && -10000 < intw && intw < 10000) {
-		/* Sort out special cases here instead of relying on pow() */
-		if (intw == 0) { 		/* x**0 is 1, even 0**0 */
-			PyFPE_START_PROTECT("pow", return 0)
-		 	if ((PyObject *)z!=Py_None) {
-			 	ix=fmod(1.0, z->ob_fval);
-			 	if (ix!=0 && z->ob_fval<0) ix+=z->ob_fval;
-			}
-		 	else ix=1.0;
-			PyFPE_END_PROTECT(ix)
-	    		return PyFloat_FromDouble(ix); 
+
+	/* Sort out special cases here instead of relying on pow() */
+	if (iw == 0) { 		/* x**0 is 1, even 0**0 */
+		PyFPE_START_PROTECT("pow", return NULL)
+		if ((PyObject *)z != Py_None) {
+			ix = fmod(1.0, z->ob_fval);
+			if (ix != 0 && z->ob_fval < 0)
+				ix += z->ob_fval;
 		}
+		else
+			ix = 1.0;
+		PyFPE_END_PROTECT(ix)
+		return PyFloat_FromDouble(ix); 
+	}
+	if (iv == 0.0) {
+		if (iw < 0.0) {
+			PyErr_SetString(PyExc_ZeroDivisionError,
+				   "0.0 to a negative power");
+			return NULL;
+		}
+		return PyFloat_FromDouble(0.0);
+	}
+
+	if (iw == intw && intw > LONG_MIN) {
+		/* ruled out LONG_MIN because -LONG_MIN isn't representable */
 		errno = 0;
-		PyFPE_START_PROTECT("pow", return 0)
+		PyFPE_START_PROTECT("pow", return NULL)
 		if (intw > 0)
 			ix = powu(iv, intw);
 		else
@@ -471,21 +484,13 @@ float_pow(PyFloatObject *v, PyObject *w, PyFloatObject *z)
 	}
 	else {
 		/* Sort out special cases here instead of relying on pow() */
-		if (iv == 0.0) {
-			if (iw < 0.0) {
-				PyErr_SetString(PyExc_ValueError,
-					   "0.0 to a negative power");
-				return NULL;
-			}
-			return PyFloat_FromDouble(0.0);
-		}
 		if (iv < 0.0) {
 			PyErr_SetString(PyExc_ValueError,
 				   "negative number to a float power");
 			return NULL;
 		}
 		errno = 0;
-		PyFPE_START_PROTECT("pow", return 0)
+		PyFPE_START_PROTECT("pow", return NULL)
 		ix = pow(iv, iw);
 		PyFPE_END_PROTECT(ix)
 	}
@@ -495,13 +500,15 @@ float_pow(PyFloatObject *v, PyObject *w, PyFloatObject *z)
 		PyErr_SetFromErrno(PyExc_OverflowError);
 		return NULL;
 	}
- 	if ((PyObject *)z!=Py_None) {
-		PyFPE_START_PROTECT("pow", return 0)
-	 	ix=fmod(ix, z->ob_fval);	/* XXX To Be Rewritten */
-	 	if ( ix!=0 &&
-		      ((iv<0 && z->ob_fval>0) || (iv>0 && z->ob_fval<0) )) {
-		     ix+=z->ob_fval;
-		    }
+	if ((PyObject *)z != Py_None) {
+		PyFPE_START_PROTECT("pow", return NULL)
+		ix = fmod(ix, z->ob_fval);	/* XXX To Be Rewritten */
+		if (ix != 0 &&
+		    ((iv < 0 && z->ob_fval > 0) ||
+		     (iv > 0 && z->ob_fval < 0)
+		    )) {
+		     ix += z->ob_fval;
+		}
 		PyFPE_END_PROTECT(ix)
 	}
 	return PyFloat_FromDouble(ix);
diff --git a/Objects/intobject.c b/Objects/intobject.c
index b88a05d..c9d1f6a 100644
--- a/Objects/intobject.c
+++ b/Objects/intobject.c
@@ -483,8 +483,12 @@ int_pow(PyIntObject *v, PyIntObject *w, PyIntObject *z)
 	iv = v->ob_ival;
 	iw = w->ob_ival;
 	if (iw < 0) {
-		PyErr_SetString(PyExc_ValueError,
-				"integer to the negative power");
+		if (iv)
+			PyErr_SetString(PyExc_ValueError,
+					"integer to a negative power");
+		else
+			PyErr_SetString(PyExc_ZeroDivisionError,
+					"0 to a negative power");
 		return NULL;
 	}
  	if ((PyObject *)z != Py_None) {
diff --git a/Objects/longobject.c b/Objects/longobject.c
index 65dcaa0..bfb431f 100644
--- a/Objects/longobject.c
+++ b/Objects/longobject.c
@@ -1244,8 +1244,12 @@ long_pow(PyLongObject *a, PyLongObject *b, PyLongObject *c)
 	
 	size_b = b->ob_size;
 	if (size_b < 0) {
-		PyErr_SetString(PyExc_ValueError,
-				"long integer to the negative power");
+		if (a->ob_size)
+			PyErr_SetString(PyExc_ValueError,
+					"long integer to a negative power");
+		else
+			PyErr_SetString(PyExc_ZeroDivisionError,
+					"zero to a negative power");
 		return NULL;
 	}
 	z = (PyLongObject *)PyLong_FromLong(1L);