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bpo-31373: fix undefined floating-point demotions (#3396)

This commit is contained in:
Benjamin Peterson 2017-09-07 11:13:59 -07:00 committed by GitHub
parent c988ae01fe
commit a853a8ba78
5 changed files with 51 additions and 30 deletions
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32
Include/pymath.h
View File

@ -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))
(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 */

2
Misc/NEWS.d/next/Core and Builtins/2017-09-06-15-25-59.bpo-31373.dC4jd4.rst Normal file
View File

@ -0,0 +1,2 @@
Fix several possible instances of undefined behavior due to floating-point
demotions.

10
Objects/floatobject.c
View File

@ -2233,13 +2233,15 @@ _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;
@ -2247,7 +2249,7 @@ _PyFloat_Pack4(double x, unsigned char *p, int le)
}
for (i = 0; i < 4; i++) {
*p = *s++;
*p = s[i];
p += incr;
}
return 0;

5
Python/getargs.c
View File

@ -4,6 +4,7 @@
#include "Python.h"
#include <ctype.h>
#include <float.h>
#ifdef __cplusplus
@ -858,6 +859,10 @@ 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;

32
Python/pytime.c
View File

@ -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;
}