SF bug #513866: Float/long comparison anomaly.
When an integer is compared to a float now, the int isn't coerced to float.
This avoids spurious overflow exceptions and insane results. This should
compute correct results, without raising spurious exceptions, in all cases
now -- although I expect that what happens when an int/long is compared to
a NaN is still a platform accident.
Note that we had potential problems here even with "short" ints, on boxes
where sizeof(long)==8. There's #ifdef'ed code here to handle that, but
I can't test it as intended. I tested it by changing the #ifdef to
trigger on my 32-bit box instead.
I suppose this is a bugfix candidate, but I won't backport it. It's
long-winded (for speed) and messy (because the problem is messy). Note
that this also depends on a previous 2.4 patch that introduced
_Py_SwappedOp[] as an extern.
diff --git a/Lib/test/test_long.py b/Lib/test/test_long.py
index 1a04ce9..74ae7c6 100644
--- a/Lib/test/test_long.py
+++ b/Lib/test/test_long.py
@@ -387,8 +387,7 @@
"1. ** huge", "huge ** 1.", "1. ** mhuge", "mhuge ** 1.",
"math.sin(huge)", "math.sin(mhuge)",
"math.sqrt(huge)", "math.sqrt(mhuge)", # should do better
- "math.floor(huge)", "math.floor(mhuge)",
- "float(shuge) == int(shuge)"]:
+ "math.floor(huge)", "math.floor(mhuge)"]:
try:
eval(test, namespace)
@@ -397,6 +396,11 @@
else:
raise TestFailed("expected OverflowError from %s" % test)
+ # XXX Perhaps float(shuge) can raise OverflowError on some box?
+ # The comparison should not.
+ if float(shuge) == int(shuge):
+ raise TestFailed("float(shuge) should not equal int(shuge)")
+
# ---------------------------------------------- test huge log and log10
def test_logs():
@@ -431,6 +435,101 @@
except ValueError:
pass
+# ----------------------------------------------- test mixed comparisons
+
+def test_mixed_compares():
+ import math
+ import sys
+
+ if verbose:
+ print "mixed comparisons"
+
+ # We're mostly concerned with that mixing floats and longs does the
+ # right stuff, even when longs are too large to fit in a float.
+ # The safest way to check the results is to use an entirely different
+ # method, which we do here via a skeletal rational class (which
+ # represents all Python ints, longs and floats exactly).
+ class Rat:
+ def __init__(self, value):
+ if isinstance(value, (int, long)):
+ self.n = value
+ self.d = 1
+
+ elif isinstance(value, float):
+ # Convert to exact rational equivalent.
+ f, e = math.frexp(abs(value))
+ assert f == 0 or 0.5 <= f < 1.0
+ # |value| = f * 2**e exactly
+
+ # Suck up CHUNK bits at a time; 28 is enough so that we suck
+ # up all bits in 2 iterations for all known binary double-
+ # precision formats, and small enough to fit in an int.
+ CHUNK = 28
+ top = 0
+ # invariant: |value| = (top + f) * 2**e exactly
+ while f:
+ f = math.ldexp(f, CHUNK)
+ digit = int(f)
+ assert digit >> CHUNK == 0
+ top = (top << CHUNK) | digit
+ f -= digit
+ assert 0.0 <= f < 1.0
+ e -= CHUNK
+
+ # Now |value| = top * 2**e exactly.
+ if e >= 0:
+ n = top << e
+ d = 1
+ else:
+ n = top
+ d = 1 << -e
+ if value < 0:
+ n = -n
+ self.n = n
+ self.d = d
+ assert float(n) / float(d) == value
+
+ else:
+ raise TypeError("can't deal with %r" % val)
+
+ def __cmp__(self, other):
+ if not isinstance(other, Rat):
+ other = Rat(other)
+ return cmp(self.n * other.d, self.d * other.n)
+
+ cases = [0, 0.001, 0.99, 1.0, 1.5, 1e20, 1e200]
+ # 2**48 is an important boundary in the internals. 2**53 is an
+ # important boundary for IEEE double precision.
+ for t in 2.0**48, 2.0**50, 2.0**53:
+ cases.extend([t - 1.0, t - 0.3, t, t + 0.3, t + 1.0,
+ long(t-1), long(t), long(t+1)])
+ cases.extend([0, 1, 2, sys.maxint, float(sys.maxint)])
+ # 1L<<20000 should exceed all double formats. long(1e200) is to
+ # check that we get equality with 1e200 above.
+ t = long(1e200)
+ cases.extend([0L, 1L, 2L, 1L << 20000, t-1, t, t+1])
+ cases.extend([-x for x in cases])
+ for x in cases:
+ Rx = Rat(x)
+ for y in cases:
+ Ry = Rat(y)
+ Rcmp = cmp(Rx, Ry)
+ xycmp = cmp(x, y)
+ if Rcmp != xycmp:
+ raise TestFailed('%r %r %d %d' % (x, y, Rcmp, xycmp))
+ if (x == y) != (Rcmp == 0):
+ raise TestFailed('%r == %r %d' % (x, y, Rcmp))
+ if (x != y) != (Rcmp != 0):
+ raise TestFailed('%r != %r %d' % (x, y, Rcmp))
+ if (x < y) != (Rcmp < 0):
+ raise TestFailed('%r < %r %d' % (x, y, Rcmp))
+ if (x <= y) != (Rcmp <= 0):
+ raise TestFailed('%r <= %r %d' % (x, y, Rcmp))
+ if (x > y) != (Rcmp > 0):
+ raise TestFailed('%r > %r %d' % (x, y, Rcmp))
+ if (x >= y) != (Rcmp >= 0):
+ raise TestFailed('%r >= %r %d' % (x, y, Rcmp))
+
# ---------------------------------------------------------------- do it
test_division()
@@ -441,3 +540,4 @@
test_auto_overflow()
test_float_overflow()
test_logs()
+test_mixed_compares()
diff --git a/Misc/NEWS b/Misc/NEWS
index 3c2734b..89a6c57 100644
--- a/Misc/NEWS
+++ b/Misc/NEWS
@@ -15,7 +15,14 @@
- The bytecode optimizer now folds tuples of constants into a single
constant.
-- PyLong_AsUnsignedLong[Mask] now support int objects as well.
+- SF bug #513866: Float/long comparison anomaly. Prior to 2.4b1, when
+ an integer was compared to a float, the integer was coerced to a float.
+ That could yield spurious overflow errors (if the integer was very
+ large), and to anomalies such as
+ ``long(1e200)+1 == 1e200 == long(1e200)-1``. Coercion to float is no
+ longer performed, and cases like ``long(1e200)-1 < 1e200``,
+ ``long(1e200)+1 > 1e200`` and ``(1 << 20000) > 1e200`` are computed
+ correctly now.
Extension modules
-----------------
@@ -72,6 +79,8 @@
C API
-----
+- PyLong_AsUnsignedLong[Mask] now support int objects as well.
+
- SF patch #998993: ``PyUnicode_DecodeUTF8Stateful`` and
``PyUnicode_DecodeUTF16Stateful`` have been added, which implement stateful
decoding.
diff --git a/Objects/floatobject.c b/Objects/floatobject.c
index 774d2ea..46c05b2 100644
--- a/Objects/floatobject.c
+++ b/Objects/floatobject.c
@@ -354,38 +354,236 @@
return PyString_FromString(buf);
}
+/* Comparison is pretty much a nightmare. When comparing float to float,
+ * we do it as straightforwardly (and long-windedly) as conceivable, so
+ * that, e.g., Python x == y delivers the same result as the platform
+ * C x == y when x and/or y is a NaN.
+ * When mixing float with an integer type, there's no good *uniform* approach.
+ * Converting the double to an integer obviously doesn't work, since we
+ * may lose info from fractional bits. Converting the integer to a double
+ * also has two failure modes: (1) a long int may trigger overflow (too
+ * large to fit in the dynamic range of a C double); (2) even a C long may have
+ * more bits than fit in a C double (e.g., on a a 64-bit box long may have
+ * 63 bits of precision, but a C double probably has only 53), and then
+ * we can falsely claim equality when low-order integer bits are lost by
+ * coercion to double. So this part is painful too.
+ */
+
static PyObject*
float_richcompare(PyObject *v, PyObject *w, int op)
{
double i, j;
int r = 0;
- CONVERT_TO_DOUBLE(v, i);
- CONVERT_TO_DOUBLE(w, j);
+ assert(PyFloat_Check(v));
+ i = PyFloat_AS_DOUBLE(v);
+ /* Switch on the type of w. Set i and j to doubles to be compared,
+ * and op to the richcomp to use.
+ */
+ if (PyFloat_Check(w))
+ j = PyFloat_AS_DOUBLE(w);
+
+ else if (Py_IS_INFINITY(i)) {
+ /* XXX If we had a reliable way to check whether i is a
+ * XXX NaN, it would belong in this branch too.
+ */
+ if (PyInt_Check(w) || PyLong_Check(w))
+ /* The magnitude of i exceeds any finite integer,
+ * so it doesn't matter which int we compare i with.
+ */
+ j = 0.0;
+ else
+ goto Unimplemented;
+ }
+
+ else if (PyInt_Check(w)) {
+ long jj = PyInt_AS_LONG(w);
+ /* In the worst realistic case I can imagine, C double is a
+ * Cray single with 48 bits of precision, and long has 64
+ * bits.
+ */
+#if SIZEOF_LONG > 4
+ unsigned long abs = (unsigned long)(jj < 0 ? -jj : jj);
+ if (abs >> 48) {
+ /* Needs more than 48 bits. Make it take the
+ * PyLong path.
+ */
+ PyObject *result;
+ PyObject *ww = PyLong_FromLong(jj);
+
+ if (ww == NULL)
+ return NULL;
+ result = float_richcompare(v, ww, op);
+ Py_DECREF(ww);
+ return result;
+ }
+#endif
+ j = (double)jj;
+ assert((long)j == jj);
+ }
+
+ else if (PyLong_Check(w)) {
+ int vsign = i == 0.0 ? 0 : i < 0.0 ? -1 : 1;
+ int wsign = _PyLong_Sign(w);
+ size_t nbits;
+ double mant;
+ int exponent;
+
+ if (vsign != wsign) {
+ /* Magnitudes are irrelevant -- the signs alone
+ * determine the outcome.
+ */
+ i = (double)vsign;
+ j = (double)wsign;
+ goto Compare;
+ }
+ /* The signs are the same. */
+ /* Convert w to a double if it fits. In particular, 0 fits. */
+ nbits = _PyLong_NumBits(w);
+ if (nbits == (size_t)-1 && PyErr_Occurred()) {
+ /* This long is so large that size_t isn't big enough
+ * to hold the # of Python digits. Replace with
+ * little doubles that give the same outcome --
+ * w is so large that its magnitude must exceed
+ * the magnitude of any finite float.
+ */
+ PyErr_Clear();
+ i = (double)vsign;
+ assert(wsign != 0);
+ j = wsign * 2.0;
+ goto Compare;
+ }
+ if (nbits <= 48) {
+ j = PyLong_AsDouble(w);
+ /* It's impossible that <= 48 bits overflowed. */
+ assert(j != -1.0 || ! PyErr_Occurred());
+ goto Compare;
+ }
+ assert(wsign != 0); /* else nbits was 0 */
+ assert(vsign != 0); /* if vsign were 0, then since wsign is
+ * not 0, we would have taken the
+ * vsign != wsign branch at the start */
+ /* We want to work with non-negative numbers. */
+ if (vsign < 0) {
+ /* "Multiply both sides" by -1; this also swaps the
+ * comparator.
+ */
+ i = -i;
+ op = _Py_SwappedOp[op];
+ }
+ assert(i > 0.0);
+ mant = frexp(i, &exponent);
+ /* exponent is the # of bits in v before the radix point;
+ * we know that nbits (the # of bits in w) > 48 at this point
+ */
+ if (exponent < 0 || (size_t)exponent < nbits) {
+ i = 1.0;
+ j = 2.0;
+ goto Compare;
+ }
+ if ((size_t)exponent > nbits) {
+ i = 2.0;
+ j = 1.0;
+ goto Compare;
+ }
+ /* v and w have the same number of bits before the radix
+ * point. Construct two longs that have the same comparison
+ * outcome.
+ */
+ {
+ double fracpart;
+ double intpart;
+ PyObject *result = NULL;
+ PyObject *one = NULL;
+ PyObject *vv = NULL;
+ PyObject *ww = w;
+
+ if (wsign < 0) {
+ ww = PyNumber_Negative(w);
+ if (ww == NULL)
+ goto Error;
+ }
+ else
+ Py_INCREF(ww);
+
+ fracpart = modf(i, &intpart);
+ vv = PyLong_FromDouble(intpart);
+ if (vv == NULL)
+ goto Error;
+
+ if (fracpart != 0.0) {
+ /* Shift left, and or a 1 bit into vv
+ * to represent the lost fraction.
+ */
+ PyObject *temp;
+
+ one = PyInt_FromLong(1);
+ if (one == NULL)
+ goto Error;
+
+ temp = PyNumber_Lshift(ww, one);
+ if (temp == NULL)
+ goto Error;
+ Py_DECREF(ww);
+ ww = temp;
+
+ temp = PyNumber_Lshift(vv, one);
+ if (temp == NULL)
+ goto Error;
+ Py_DECREF(vv);
+ vv = temp;
+
+ temp = PyNumber_Or(vv, one);
+ if (temp == NULL)
+ goto Error;
+ Py_DECREF(vv);
+ vv = temp;
+ }
+
+ r = PyObject_RichCompareBool(vv, ww, op);
+ if (r < 0)
+ goto Error;
+ result = PyBool_FromLong(r);
+ Error:
+ Py_XDECREF(vv);
+ Py_XDECREF(ww);
+ Py_XDECREF(one);
+ return result;
+ }
+ } /* else if (PyLong_Check(w)) */
+
+ else /* w isn't float, int, or long */
+ goto Unimplemented;
+
+ Compare:
PyFPE_START_PROTECT("richcompare", return NULL)
switch (op) {
case Py_EQ:
- r = i==j;
+ r = i == j;
break;
case Py_NE:
- r = i!=j;
+ r = i != j;
break;
case Py_LE:
- r = i<=j;
+ r = i <= j;
break;
case Py_GE:
- r = i>=j;
+ r = i >= j;
break;
case Py_LT:
- r = i<j;
+ r = i < j;
break;
case Py_GT:
- r = i>j;
+ r = i > j;
break;
}
PyFPE_END_PROTECT(r)
return PyBool_FromLong(r);
+
+ Unimplemented:
+ Py_INCREF(Py_NotImplemented);
+ return Py_NotImplemented;
}
static long