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

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merged 1 commit into from
Sep 7, 2017
Merged

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

merged 1 commit into from
Sep 7, 2017

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benjaminp
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@benjaminp benjaminp commented Sep 6, 2017 •
edited by bedevere-bot
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@benjaminp benjaminp requested a review from vstinner September 6, 2017 22:26
@benjaminp benjaminp force-pushed the benjamin-undefined-downcast branch from d15a9ef to 60ec3e7 Compare September 6, 2017 23:15
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vstinner requested changes Sep 6, 2017
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Misc/NEWS.d/next/Core and Builtins/2017-09-06-15-25-59.bpo-31373.dC4jd4.rst Outdated
Fix several possible instances of undefined behavior due to floating-point
demotions.

# Write your Misc/NEWS entry below. It should be a simple ReST paragraph. #
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You are not supposed to commit this part :-)

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hmm, blurb hiccup I guess

Python/getargs.c
@@ -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)
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I would prefer to use FLT_MIN.

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FLT_MIN is the smallest nonnegative float not what we want here.

Objects/floatobject.c
goto Overflow;

unsigned char s[sizeof(float)];
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I would be more confident with an assert(sizeof(float) == 4); just in case.

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This code only executes if floats are in IEE754 format and are therefore 4 bytes.

Objects/floatobject.c
int i, incr = 1;

if (Py_IS_INFINITY(y) && !Py_IS_INFINITY(x))
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I don't understand why you remove Py_IS_INFINITY(y).

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y is no longer defined at this point.

Include/pymath.h Outdated
@@ -215,4 +215,16 @@ PyAPI_FUNC(void) _Py_set_387controlword(unsigned short);
(X) == -Py_HUGE_VAL))
#endif

/* Return whether integral type *type* is signed or not. */
#define _Py_IntegralSigned(type) ((type)(-1) < 0)
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I suggest to put "Type" in the macro names. Maybe _Py_IsTypeSigned(type), _Py_TypeMax(), etc.?

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sg

Include/pymath.h Outdated
* 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_IntegralInRange(type, v) (_Py_IntegralMin(type) <= v && v <= _Py_IntegralMax(type))
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_Py_IsInTypeRange(type, v)?

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A Python core developer has requested some changes be made to your pull request before we can consider merging it. If you could please address their requests along with any other requests in other reviews from core developers that would be appreciated.

Once you have made the requested changes, please leave a comment on this pull request containing the phrase I didn't expect the Spanish Inquisition!. I will then notify any core developers who have left a review that you're ready for them to take another look at this pull request.

@benjaminp benjaminp force-pushed the benjamin-undefined-downcast branch 5 times, most recently from 7e4b497 to 4d7578b Compare September 7, 2017 02:21
@benjaminp benjaminp force-pushed the benjamin-undefined-downcast branch from 4d7578b to c120b8b Compare September 7, 2017 02:33
@benjaminp benjaminp merged commit a853a8b into master Sep 7, 2017
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🐍🍒⛏🤖 Thanks @benjaminp for the PR, and @benjaminp for merging it 🌮🎉.I'm working now to backport this PR to: 3.6.

@benjaminp benjaminp deleted the benjamin-undefined-downcast branch September 7, 2017 18:14
miss-islington pushed a commit to miss-islington/cpython that referenced this pull request Sep 7, 2017
@benjaminp @miss-islington
[3.6] bpo-31373: fix undefined floating-point demotions (pythonGH-3396)
f772e11 
(cherry picked from commit a853a8b)
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GH-3424 is a backport of this pull request to the 3.6 branch.

benjaminp pushed a commit that referenced this pull request Sep 7, 2017
@miss-islington @benjaminp
[3.6] fixes bpo-31373: fix undefined floating-point demotions (GH-3396)…
b036232 
… (#3424)

(cherry picked from commit a853a8b)
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