[Python-checkins] [3.6] fixes bpo-31373: fix undefined floating-point demotions (GH-3396) (#3424)
Benjamin Peterson
webhook-mailer at python.org
Thu Sep 7 14:35:06 EDT 2017
https://github.com/python/cpython/commit/b03623227ed1264e3cac4e6bb4878d96b91aa484
commit: b03623227ed1264e3cac4e6bb4878d96b91aa484
branch: 3.6
author: Miss Islington (bot) <31488909+miss-islington at users.noreply.github.com>
committer: Benjamin Peterson <benjamin at python.org>
date: 2017-09-07T11:35:03-07:00
summary:
[3.6] fixes bpo-31373: fix undefined floating-point demotions (GH-3396) (#3424)
(cherry picked from commit a853a8ba7850381d49b284295dd6f0dc491dbe44)
files:
A Misc/NEWS.d/next/Core and Builtins/2017-09-06-15-25-59.bpo-31373.dC4jd4.rst
M Include/pymath.h
M Objects/floatobject.c
M Python/getargs.c
M Python/pytime.c
diff --git a/Include/pymath.h b/Include/pymath.h
index 7216a092d17..6cf69f98acf 100644
--- a/Include/pymath.h
+++ b/Include/pymath.h
@@ -187,14 +187,14 @@ PyAPI_FUNC(void) _Py_set_387controlword(unsigned short);
* result.
* Caution:
* This isn't reliable. C99 no longer requires libm to set errno under
- * any exceptional condition, but does require +- HUGE_VAL return
- * values on overflow. A 754 box *probably* maps HUGE_VAL to a
- * double infinity, and we're cool if that's so, unless the input
- * was an infinity and an infinity is the expected result. A C89
- * system sets errno to ERANGE, so we check for that too. We're
- * out of luck if a C99 754 box doesn't map HUGE_VAL to +Inf, or
- * if the returned result is a NaN, or if a C89 box returns HUGE_VAL
- * in non-overflow cases.
+ * any exceptional condition, but does require +- HUGE_VAL return
+ * values on overflow. A 754 box *probably* maps HUGE_VAL to a
+ * double infinity, and we're cool if that's so, unless the input
+ * was an infinity and an infinity is the expected result. A C89
+ * system sets errno to ERANGE, so we check for that too. We're
+ * out of luck if a C99 754 box doesn't map HUGE_VAL to +Inf, or
+ * if the returned result is a NaN, or if a C89 box returns HUGE_VAL
+ * in non-overflow cases.
* X is evaluated more than once.
* Some platforms have better way to spell this, so expect some #ifdef'ery.
*
@@ -211,8 +211,20 @@ PyAPI_FUNC(void) _Py_set_387controlword(unsigned short);
#define Py_OVERFLOWED(X) isinf(X)
#else
#define Py_OVERFLOWED(X) ((X) != 0.0 && (errno == ERANGE || \
- (X) == Py_HUGE_VAL || \
- (X) == -Py_HUGE_VAL))
-#endif
+ (X) == Py_HUGE_VAL || \
+ (X) == -Py_HUGE_VAL))
+#endif
+
+/* Return whether integral type *type* is signed or not. */
+#define _Py_IntegralTypeSigned(type) ((type)(-1) < 0)
+/* Return the maximum value of integral type *type*. */
+#define _Py_IntegralTypeMax(type) ((_Py_IntegralTypeSigned(type)) ? (((((type)1 << (sizeof(type)*CHAR_BIT - 2)) - 1) << 1) + 1) : ~(type)0)
+/* Return the minimum value of integral type *type*. */
+#define _Py_IntegralTypeMin(type) ((_Py_IntegralTypeSigned(type)) ? -_Py_IntegralTypeMax(type) - 1 : 0)
+/* Check whether *v* is in the range of integral type *type*. This is most
+ * useful if *v* is floating-point, since demoting a floating-point *v* to an
+ * integral type that cannot represent *v*'s integral part is undefined
+ * behavior. */
+#define _Py_InIntegralTypeRange(type, v) (_Py_IntegralTypeMin(type) <= v && v <= _Py_IntegralTypeMax(type))
#endif /* Py_PYMATH_H */
diff --git a/Misc/NEWS.d/next/Core and Builtins/2017-09-06-15-25-59.bpo-31373.dC4jd4.rst b/Misc/NEWS.d/next/Core and Builtins/2017-09-06-15-25-59.bpo-31373.dC4jd4.rst
new file mode 100644
index 00000000000..3ffb4093470
--- /dev/null
+++ b/Misc/NEWS.d/next/Core and Builtins/2017-09-06-15-25-59.bpo-31373.dC4jd4.rst
@@ -0,0 +1,2 @@
+Fix several possible instances of undefined behavior due to floating-point
+demotions.
diff --git a/Objects/floatobject.c b/Objects/floatobject.c
index 80bf71efd21..1803a683ba0 100644
--- a/Objects/floatobject.c
+++ b/Objects/floatobject.c
@@ -2182,13 +2182,15 @@ _PyFloat_Pack4(double x, unsigned char *p, int le)
}
else {
- float y = (float)x;
- const unsigned char *s = (unsigned char*)&y;
int i, incr = 1;
- if (Py_IS_INFINITY(y) && !Py_IS_INFINITY(x))
+ if (fabs(x) > FLT_MAX && !Py_IS_INFINITY(x))
goto Overflow;
+ unsigned char s[sizeof(float)];
+ float y = (float)x;
+ memcpy(s, &y, sizeof(float));
+
if ((float_format == ieee_little_endian_format && !le)
|| (float_format == ieee_big_endian_format && le)) {
p += 3;
@@ -2196,7 +2198,7 @@ _PyFloat_Pack4(double x, unsigned char *p, int le)
}
for (i = 0; i < 4; i++) {
- *p = *s++;
+ *p = s[i];
p += incr;
}
return 0;
diff --git a/Python/getargs.c b/Python/getargs.c
index 616c6eb1073..8fb19f34ecb 100644
--- a/Python/getargs.c
+++ b/Python/getargs.c
@@ -4,6 +4,7 @@
#include "Python.h"
#include <ctype.h>
+#include <float.h>
#ifdef __cplusplus
@@ -810,6 +811,10 @@ convertsimple(PyObject *arg, const char **p_format, va_list *p_va, int flags,
double dval = PyFloat_AsDouble(arg);
if (PyErr_Occurred())
RETURN_ERR_OCCURRED;
+ else if (dval > FLT_MAX)
+ *p = (float)INFINITY;
+ else if (dval < -FLT_MAX)
+ *p = (float)-INFINITY;
else
*p = (float) dval;
break;
diff --git a/Python/pytime.c b/Python/pytime.c
index 3015a6be0b8..387657af2cf 100644
--- a/Python/pytime.c
+++ b/Python/pytime.c
@@ -97,7 +97,7 @@ static int
_PyTime_DoubleToDenominator(double d, time_t *sec, long *numerator,
double denominator, _PyTime_round_t round)
{
- double intpart, err;
+ double intpart;
/* volatile avoids optimization changing how numbers are rounded */
volatile double floatpart;
@@ -115,14 +115,13 @@ _PyTime_DoubleToDenominator(double d, time_t *sec, long *numerator,
}
assert(0.0 <= floatpart && floatpart < denominator);
- *sec = (time_t)intpart;
- *numerator = (long)floatpart;
-
- err = intpart - (double)*sec;
- if (err <= -1.0 || err >= 1.0) {
+ if (!_Py_InIntegralTypeRange(time_t, intpart)) {
error_time_t_overflow();
return -1;
}
+ *sec = (time_t)intpart;
+ *numerator = (long)floatpart;
+
return 0;
}
@@ -150,7 +149,7 @@ int
_PyTime_ObjectToTime_t(PyObject *obj, time_t *sec, _PyTime_round_t round)
{
if (PyFloat_Check(obj)) {
- double intpart, err;
+ double intpart;
/* volatile avoids optimization changing how numbers are rounded */
volatile double d;
@@ -158,12 +157,11 @@ _PyTime_ObjectToTime_t(PyObject *obj, time_t *sec, _PyTime_round_t round)
d = _PyTime_Round(d, round);
(void)modf(d, &intpart);
- *sec = (time_t)intpart;
- err = intpart - (double)*sec;
- if (err <= -1.0 || err >= 1.0) {
+ if (!_Py_InIntegralTypeRange(time_t, intpart)) {
error_time_t_overflow();
return -1;
}
+ *sec = (time_t)intpart;
return 0;
}
else {
@@ -180,7 +178,9 @@ _PyTime_ObjectToTimespec(PyObject *obj, time_t *sec, long *nsec,
{
int res;
res = _PyTime_ObjectToDenominator(obj, sec, nsec, 1e9, round);
- assert(0 <= *nsec && *nsec < SEC_TO_NS);
+ if (res == 0) {
+ assert(0 <= *nsec && *nsec < SEC_TO_NS);
+ }
return res;
}
@@ -190,7 +190,9 @@ _PyTime_ObjectToTimeval(PyObject *obj, time_t *sec, long *usec,
{
int res;
res = _PyTime_ObjectToDenominator(obj, sec, usec, 1e6, round);
- assert(0 <= *usec && *usec < SEC_TO_US);
+ if (res == 0) {
+ assert(0 <= *usec && *usec < SEC_TO_US);
+ }
return res;
}
@@ -276,7 +278,6 @@ static int
_PyTime_FromFloatObject(_PyTime_t *t, double value, _PyTime_round_t round,
long unit_to_ns)
{
- double err;
/* volatile avoids optimization changing how numbers are rounded */
volatile double d;
@@ -285,12 +286,11 @@ _PyTime_FromFloatObject(_PyTime_t *t, double value, _PyTime_round_t round,
d *= (double)unit_to_ns;
d = _PyTime_Round(d, round);
- *t = (_PyTime_t)d;
- err = d - (double)*t;
- if (fabs(err) >= 1.0) {
+ if (!_Py_InIntegralTypeRange(_PyTime_t, d)) {
_PyTime_overflow();
return -1;
}
+ *t = (_PyTime_t)d;
return 0;
}
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