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.

Lib/test/test_pow.py

@@ -2,44 +2,69 @@ import sys
 import test_support
 
 def powtest(type):
-    if (type!=float): 
+    if type != float: 
         print "    Testing 2-argument pow() function..."
         for i in range(-1000, 1000):
-            if (pow(type(i),0)!=1): 
+            if pow(type(i), 0) != 1: 
                 raise ValueError, 'pow('+str(i)+',0) != 1'
-            if (pow(type(i),1)!=type(i)):
+            if pow(type(i), 1) != type(i):
                 raise ValueError, 'pow('+str(i)+',1) != '+str(i)
-            if (pow(type(0),1)!=type(0)):
+            if pow(type(0), 1) != type(0):
                 raise ValueError, 'pow(0,'+str(i)+') != 0'
-            if (pow(type(1),1)!=type(1)):
+            if pow(type(1), 1) != type(1):
                 raise ValueError, 'pow(1,'+str(i)+') != 1'
-            
+
         for i in range(-100, 100):
-            if (pow(type(i),3)!=i*i*i):
+            if pow(type(i), 3) != i*i*i:
                 raise ValueError, 'pow('+str(i)+',3) != '+str(i*i*i)
     
-        pow2=1
+        pow2 = 1
         for i in range(0,31):
-            if (pow(2,i)!=pow2):
+            if pow(2, i) != pow2:
                 raise ValueError, 'pow(2,'+str(i)+') != '+str(pow2)
-            if (i!=30): pow2=pow2*2
+            if i != 30 : pow2 = pow2*2
+
+        for othertype in int, long:
+            for i in range(-10, 0) + range(1, 10):
+                ii = type(i)
+                for j in range(1, 11):
+                    jj = -othertype(j)
+                    try:
+                        pow(ii, jj)
+                    except ValueError:
+                        pass # taking an int to a neg int power should fail
+                    else:
+                        raise ValueError, "pow(%s, %s) did not fail" % (ii, jj)
+
+    for othertype in int, long, float:
+        for i in range(1, 100):
+            zero = type(0)
+            exp = -othertype(i/10.0)
+            if exp == 0:
+                continue
+            try:
+                pow(zero, exp)
+            except ZeroDivisionError:
+                pass # taking zero to any negative exponent should fail
+            else:
+                raise ValueError, "pow(%s, %s) did not fail" % (zero, exp)
 
     print "    Testing 3-argument pow() function..."
     il, ih = -20, 20
     jl, jh = -5,   5
     kl, kh = -10, 10
     compare = cmp
-    if (type==float):
-        il=1
+    if type == float:
+        il = 1
         compare = test_support.fcmp
-    elif (type==int):
-        jl=0
-    elif (type==long):
-        jl,jh = 0, 15
+    elif type == int:
+        jl = 0
+    elif type == long:
+        jl, jh = 0, 15
     for i in range(il, ih+1):
-         for j in range(jl,jh+1):
+         for j in range(jl, jh+1):
              for k in range(kl, kh+1):
-                 if (k!=0):
+                 if k != 0:
                      if compare(pow(type(i),j,k), pow(type(i),j)% type(k)):
                          raise ValueError, "pow(" +str(i)+ "," +str(j)+ \
                               "," +str(k)+ ") != pow(" +str(i)+ "," + \
@@ -81,15 +106,15 @@ print
 for i in range(-10, 11):
  for j in range(0, 6):
   for k in range(-7, 11):
-   if (j>=0 and k!=0):
-    o=pow(i,j) % k
-    n=pow(i,j,k)
-    if (o!=n): print 'Integer mismatch:', i,j,k
-   if (j>=0 and k<>0):
-    o=pow(long(i),j) % k
-    n=pow(long(i),j,k)
-    if (o!=n): print 'Long mismatch:', i,j,k
-   if (i>=0 and k<>0):
-     o=pow(float(i),j) % k
-     n=pow(float(i),j,k)
-     if (o!=n): print 'Float mismatch:', i,j,k
+   if j >= 0 and k != 0:
+    o = pow(i,j) % k
+    n = pow(i,j,k)
+    if o != n: print 'Integer mismatch:', i,j,k
+   if j >= 0 and k <> 0:
+    o = pow(long(i),j) % k
+    n = pow(long(i),j,k)
+    if o != n: print 'Long mismatch:', i,j,k
+   if i >= 0 and k <> 0:
+     o = pow(float(i),j) % k
+     n = pow(float(i),j,k)
+     if o != n: print 'Float mismatch:', i,j,k

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);

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) {

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);