[3.13] gh-99880: document rounding mode for new-style formatting (GH-121481) #126334
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…onGH-121481) * pythongh-99880: document rounding mode for new-style formatting The CPython uses _Py_dg_dtoa(), which does rounding to nearest with half to even tie-breaking rule. If that functions is unavailable, PyOS_double_to_string() fallbacks to system snprintf(). Since CPython 3.12, build requirements include C11 compiler *and* support for IEEE 754 floating point numbers (Annex F). This means that FE_TONEAREST macro is available and, per default, printf-like functions should use same rounding mode as _Py_dg_dtoa(). * Update Doc/library/string.rst Co-authored-by: Bénédikt Tran <10796600+picnixz@users.noreply.github.com> --------- (cherry picked from commit 7d7d56d) Co-authored-by: Sergey B Kirpichev <skirpichev@gmail.com> Co-authored-by: Bénédikt Tran <10796600+picnixz@users.noreply.github.com>
This was referenced Nov 2, 2024
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The CPython uses _Py_dg_dtoa(), which does rounding to nearest with half
to even tie-breaking rule.
If that functions is unavailable, PyOS_double_to_string() fallbacks to
system snprintf(). Since CPython 3.12, build requirements include C11
compiler and support for IEEE 754 floating point numbers (Annex F).
This means that FE_TONEAREST macro is available and, per default,
printf-like functions should use same rounding mode as _Py_dg_dtoa().
Co-authored-by: Bénédikt Tran 10796600+picnixz@users.noreply.github.com
(cherry picked from commit 7d7d56d)
Co-authored-by: Sergey B Kirpichev skirpichev@gmail.com
Co-authored-by: Bénédikt Tran 10796600+picnixz@users.noreply.github.com
📚 Documentation preview 📚: https://cpython-previews--126334.org.readthedocs.build/