[issue46917] Require IEEE 754 floating point to build Python 3.11

[STINNER Victor]

STINNER Victor  added the comment:

> Remove code handling missing NAN and infinity: float("nan"), float("inf"), 
> math.nan and math.inf are always available.

The code to support missing NaN was already removed by:

New changeset 1b2611eb0283055835e5df632a7a735db8c894b8 by Victor Stinner in 
branch 'main':
bpo-46656: Remove Py_NO_NAN macro (GH-31160)
https://github.com/python/cpython/commit/1b2611eb0283055835e5df632a7a735db8c894b8

In fact, math.inf is already always available in Python 3.10 and older. There 
was no "#ifdef" for missing infinity support. In Python 3.10, math.inf is 
implemented as:

static double
m_inf(void)
{
#ifndef PY_NO_SHORT_FLOAT_REPR
return _Py_dg_infinity(0);
#else
return Py_HUGE_VAL;
#endif
}

--

___
Python tracker 

___
___
Python-bugs-list mailing list
Unsubscribe: 
https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com

[issue46917] Require IEEE 754 floating point to build Python 3.11

[STINNER Victor]

STINNER Victor  added the comment:

> bpo-46917: math.nan is now always available (GH-31793)

Technically, it was already the case in practice: see bpo-46656 for the 
rationale and the history of Py_NAN.

--

___
Python tracker 

___
___
Python-bugs-list mailing list
Unsubscribe: 
https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com

[issue46917] Require IEEE 754 floating point to build Python 3.11

[STINNER Victor]

STINNER Victor  added the comment:


New changeset 7854012077009b9f364f198a8ae38b546ec58313 by Victor Stinner in 
branch 'main':
bpo-46917: math.nan is now always available (GH-31793)
https://github.com/python/cpython/commit/7854012077009b9f364f198a8ae38b546ec58313


--

___
Python tracker 

___
___
Python-bugs-list mailing list
Unsubscribe: 
https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com

[issue46917] Require IEEE 754 floating point to build Python 3.11

[STINNER Victor]

STINNER Victor  added the comment:

See also bpo-46906 "Add PyFloat_(Pack|Unpack)(2|4|8) to the public C API": the 
implementation supports non-IEEE 754 formats. Once the public C API is added, 
support for non-IEEE 754 formats should be removed.

--

___
Python tracker 

___
___
Python-bugs-list mailing list
Unsubscribe: 
https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com

[issue46917] Require IEEE 754 floating point to build Python 3.11

[STINNER Victor]

Change by STINNER Victor :


--
pull_requests: +29897
pull_request: https://github.com/python/cpython/pull/31793

___
Python tracker 

___
___
Python-bugs-list mailing list
Unsubscribe: 
https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com

[issue46917] Require IEEE 754 floating point to build Python 3.11

[STINNER Victor]

STINNER Victor  added the comment:


New changeset 9b51fd5d137b662c940f072297b30815f37f105b by Victor Stinner in 
branch 'main':
bpo-46917: Require IEEE 754 to build Python (GH-31790)
https://github.com/python/cpython/commit/9b51fd5d137b662c940f072297b30815f37f105b


--

___
Python tracker 

___
___
Python-bugs-list mailing list
Unsubscribe: 
https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com

[issue46917] Require IEEE 754 floating point to build Python 3.11

[STINNER Victor]

Change by STINNER Victor :


--
keywords: +patch
pull_requests: +29894
stage:  -> patch review
pull_request: https://github.com/python/cpython/pull/31790

___
Python tracker 

___
___
Python-bugs-list mailing list
Unsubscribe: 
https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com

[issue46917] Require IEEE 754 floating point to build Python 3.11

[Mark Dickinson]

Mark Dickinson  added the comment:

> * Mention the new build requirement in What's New in Python 3.11.
> * Modify configure script to make it fail if the IEEE 754 support is missing.
> * Remove code handling missing NAN and infinity: float("nan"), float("inf"), 
> math.nan and math.inf are always available.

That sounds fine.

> * Remove @requires_IEEE_754 decorator of test.support and tests.

I'd suggest leaving those decorators. Some of the tests are used by Python 
implementations other than CPython, and we're not requiring IEEE 754 on all 
Python implementations.

> * Remove "unknown_format" code path of pack/unpack functions like 
> _PyFloat_Pack8() (see bpo-46906 which proposes to make these functions 
> public).

Sounds fine.

> platforms with float larger than 64-bit

I'm assuming you mean Python "float" / C "double" here. There seems to be a 
persistent misunderstanding here, and I'd really like to be sure that everyone 
understands what the current code is doing before changing anything. There are 
*no* platforms that Python cares about where the C double is larger than 
64-bits, and as far as I'm aware there never have been.

What there *is* is a set of platforms where the C double is IEEE 754 binary64 
format, but where arithmetic operations between doubles may be performed in 
extended precision (usually 64-bit precision), so those arithmetic operations 
don't conform strictly to IEEE 754 semantics. Most flavours of Linux on x86 
match that description.

Then there's a (possibly empty, but we don't know that for sure) subset of 
*that* set of platforms where we don't know how to temporarily enforce 53-bit 
precision during numeric parsing / formatting operations.

It's that second subset where dtoa.c can't be used, and where we need the 
fallback of the "legacy" float repr.

I'd be more than happy to deprecate and eventually remove support for the 
legacy float repr, but I think it's too big a change to make for 3.11: we'd 
need to deprecate the support for 3.11 and eventually remove it in 3.13.

--

___
Python tracker 

___
___
Python-bugs-list mailing list
Unsubscribe: 
https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com

[issue46917] Require IEEE 754 floating point to build Python 3.11

[STINNER Victor]

Change by STINNER Victor :


--
nosy: +mark.dickinson

___
Python tracker 

___
___
Python-bugs-list mailing list
Unsubscribe: 
https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com

[issue46917] Require IEEE 754 floating point to build Python 3.11

[STINNER Victor]

New submission from STINNER Victor :

See "[Python-Dev] Should we require IEEE 754 floating-point for CPython?" 
thread:
https://mail.python.org/archives/list/python-...@python.org/thread/J5FSP6J4EITPY5C2UJI7HSL2GQCTCUWN/

I propose to require IEEE 754 floating-point to build Python 3.11. I propose 
the following build:

* Mention the new build requirement in What's New in Python 3.11.
* Modify configure script to make it fail if the IEEE 754 support is missing.
* Remove code handling missing NAN and infinity: float("nan"), float("inf"), 
math.nan and math.inf are always available.
* Remove @requires_IEEE_754 decorator of test.support and tests.
* Remove "unknown_format" code path of pack/unpack functions like 
_PyFloat_Pack8() (see bpo-46906 which proposes to make these functions public).


The _PY_SHORT_FLOAT_REPR==0 code path is kept. For now, platforms with float 
larger than 64-bit but without HAVE_PY_SET_53BIT_PRECISION are still supported 
(but don't get "short float repr"). See GH-31592 for details.


I prepared this requirement with these two changes:

commit 1b2611eb0283055835e5df632a7a735db8c894b8
Author: Victor Stinner 
Date:   Fri Feb 25 01:32:57 2022 +0100

bpo-46656: Remove Py_NO_NAN macro (GH-31160)

Building Python now requires support for floating point Not-a-Number
(NaN): remove the Py_NO_NAN macro.

commit 5ab745fc51e159ead28b523414e52f0bcc1ef353
Author: Victor Stinner 
Date:   Sat Feb 26 00:53:27 2022 +0100

bpo-46852: Remove the float.__set_format__() method (GH-31585)

Remove the undocumented private float.__set_format__() method,
previously known as float.__set_format__() in Python 3.7. Its
docstring said: "You probably don't want to use this function. It
exists mainly to be used in Python's test suite."


By the way, building Python 3.11 now requires a C11 compiler.

--
components: Build
messages: 414485
nosy: vstinner
priority: normal
severity: normal
status: open
title: Require IEEE 754 floating point to build Python 3.11
versions: Python 3.11

___
Python tracker 

___
___
Python-bugs-list mailing list
Unsubscribe: 
https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com